Ever wonder how you could change the contents of an HTML element? Maybe you'd like to replace the text in a paragraph to reflect what a visitor has just selected from a drop down box. By manipulating an element's innerHtml you'll be able to change your text and HTML as much as you like.
Changing Text with innerHTML
Each HTML element has an innerHTML property that defines both the HTML code and the text that occurs between that element's opening and closing tag. By changing an element's innerHTML after some user interaction, you can make much more interactive pages.
However, using innerHTML requires some preparation if you want to be able to use it easily and reliably. First, you must give the element you wish to change an id. With that id in place you will be able to use the getElementById function, which works on all browsers.
After you have that set up you can now manipulate the text of an element. To start off, let's try changing the text inside a bold tag.
JavaScript Code:
<script type="text/javascript">
function changeText(){
document.getElementById('boldStuff').innerHTML = 'Fred Flinstone';
}
</script>
<p>Welcome to the site <b id='boldStuff'>dude</b> </p>
<input type='button' onclick='changeText()' value='Change Text'/>
Display:
Welcome to the site dude
You now know how to change the text in any HTML element, but what about changing the text in an element based on user input? Well, if we combine the above knowledge with a text input...
Updating Text Based on User Input
By adding a Text Input, we can take to updating our bold text with whatever the user types into the text input. Note: We updated the function a bit and set the id to boldStuff2.
JavaScript Code:
<script type="text/javascript">
function changeText2(){
var userInput = document.getElementById('userInput').value;
document.getElementById('boldStuff2').innerHTML = userInput;
}
</script>
<p>Welcome to the site <b id='boldStuff2'>dude</b> </p>
<input type='text' id='userInput' value='Enter Text Here' />
<input type='button' onclick='changeText2()' value='Change Text'/>
Display:
Welcome to the site dude
Changing HTML with innerHTML
You can also insert HTML into your elements in the exact same way. Let's say we didn't like the text that was displayed in our paragraph and wanted to updated it with some color. The following code will take the old black text and make it bright white. The only thing we're doing different here is inserting the html element span to change the color.
JavaScript Code:
<script type="text/javascript">
function changeText3(){
var oldHTML = document.getElementById('para').innerHTML;
var newHTML = "<span style='color:#ffffff'>" + oldHTML + "</span>";
document.getElementById('para').innerHTML = newHTML;
}
</script>
<p id='para'>Welcome to the site <b id='boldStuff3'>dude</b> </p>
<input type='button' onclick='changeText3()' value='Change Text'/>
Display:
Welcome to the site dude
This was a pretty simple example for changing the HTML of an element. All we did was take the old text that was in the paragraph tag and surround it in a span tag to change the color. However, there are many more things you can do by changing an element's HTML, so don't forget this useful tool!
Have you ever tried to use JavaScript to do some form validation? Did you have any trouble using JavaScript to grab the value of your text field? There's an easy way to access any HTML element, and it's through the use of id attributes and the getElementById function.
JavaScript document.getElementById
If you want to quickly access the value of an HTML input give it an id to make your life a lot easier. This small script below will check to see if there is any text in the text field "myText". The argument that getElementById requires is the id of the HTML element you wish to utilize.
JavaScript Code:
<script type="text/javascript">
function notEmpty(){
var myTextField = document.getElementById('myText');
if(myTextField.value != "")
alert("You entered: " + myTextField.value)
else
alert("Would you please enter some text?")
}
</script>
<input type='text' id='myText' />
<input type='button' onclick='notEmpty()' value='Form Checker' />
Display:
document.getElementById returned a reference to our HTML element myText. We stored this reference into a variable, myTextField, and then used the value property that all input elements have to use to grab the value the user enters.
There are other ways to accomplish what the above script does, but this is definitely a straight-forward and browser-compatible approach.
Things to Remember About getElementById
When using the getElementById function, you need to remember a few things to ensure that everything goes smoothly. You always need to remember that getElementById is a method (or function) of the document object. This means you can only access it by using document.getElementById.
Also, be sure that you set your HTML elements' id attributes if you want to be able to use this function. Without an id, you'll be dead in the water.
If you want to access the text within a non-input HTML element, then you are going to have to use the innerHTML property instead of value. The next lesson goes into more detail about the uses of innerHTML.
Comparing strings in JavaScript is quite easy, as long as you know about the equals operator and the JavaScript If Statement. This is all you need to know to find out if two strings of your choosing are equal.
Comparing one String to another String
Below we have created a fake authentication system and use an if statement to see if the user's name will grant them access to a special message.
JavaScript Code:
<script type="text/javascript">
var username = "Agent006";
if(username == "Agent007")
document.write("Welcome special agent 007");
else
document.write("Access Denied!");
document.write("<br /><br />Would you like to try again?<br /><br />");
// User enters a different name
username = "Agent007";
if(username == "Agent007")
document.write("Welcome special agent 007");
else
document.write("Access Denied!");
</script>
Display:
Access Denied!
Would you like to try again?
Welcome special agent 007
Be sure you realize that when you are comparing one string to another, you use two equals operators "==" instead of just one "=". When you use two equals operators, it means you are comparing two values.
In this case, the English translation of our program would be: "If username is equal to Agent007, then print out a welcome message; otherwise, access is denied."
Case Insensitive String Compare
Above, we used a case sensitive compare, meaning that if the capitalization wasn't exactly the same in both strings, the if statement would fail. If you would like to just check that a certain word is entered, without worrying about the capitalization, use the toLowerCase function.
JavaScript Code:
<script type="text/javascript">
var username = "someAgent";
if(username == "SomeAgent")
document.write("Welcome special agent");
else
document.write("Access Denied!");
// Now as case insensitive
document.write("<br /><br />Let's try it with toLowerCase<br /><br />");
if(username.toLowerCase() == "SomeAgent".toLowerCase())
document.write("Welcome special agent");
else
document.write("Access Denied!");
</script>
Display:
Access Denied!
Let's try it with toLowerCase
Welcome special agent
By converting both strings to lowercase, we were able to remove the problem of it failing to find a match when the capitalization was slightly off. In this case, the "s" was capitalized in the username, but not capitalized in our if statement check.
Ever want to find something in one of your JavaScript strings? Maybe even start your search halfway through the string? Well you're in luck! The string function indexOf lets you supply one required argument (the search query) and one optional argument (the offset) for all your simple searching needs.
If you are looking for a more powerful search feature, you should check out JavaScript's string search function, which has support for regular expressions, but not offsets.
String indexOf Function
As we mentioned above, indexOf has two arguments, with the second one being optional:
SearchString - What you would like to search for.
Offset (optional) - How far into the string you would like the search to begin. If you want to search the whole string, omit this argument.
indexOf Function Example
To start off with, we will be finding the position of the "www" in a typical URL string. The indexOf function will return the location of the first match that it encounters.
JavaScript Code:
<script type="text/javascript">
var aURL = "http://www.tizag.com/";
var aPosition = aURL.indexOf("www");
document.write("The position of www = " + aPosition);
</script>
Display:
The position of www = 7
If you'd like to follow along with how this function does it's counting, here's a complete breakdown:
h - 0 - no match
t - 1 - no match
t - 2 - no match
p - 3 - no match
: - 4 - no match
/ - 5 - no match
/ - 6 - no match
w - 7 - maybe match
w - 8 - maybe match
w - 9 - It's a match, return the position of the start of the match (7).
Let's see what happens when we add another www to the URL string to see if this function gets confused or not.
JavaScript Code:
<script type="text/javascript">
var aURL = "http://www.tizag.com/www.html";
var aPosition = aURL.indexOf("www");
document.write("The position of www = " + aPosition);
</script>
Display:
The position of www = 7
Looks like it returned the position of the first "www", just as we expected, so there are no surprises in this function. However, what would we do if we wanted to find the second "www"? Well, we'd have to use an offset, for starters.
indexOf Function Offset Example
If we use the indexOf function to find the first "www", then we can use that position + 1 as a way to skip the first "www" and find the second.
JavaScript Code:
<script type="text/javascript">
var aURL = "http://www.tizag.com/www.html";
var aPosition = aURL.indexOf("www");
var secondPos = aURL.indexOf("www", aPosition + 1);
document.write("The position of www = " + aPosition);
document.write("<br />The position of the second www = " + secondPos);
</script>
Display:
The position of www = 7
The position of the second www = 21
By using an offset of 8 (7 + 1), we were able to skip the first "www" to instead find the second. In case you're interested in what the function was actually looking at after we gave an offset, we have it below:
ww.tizag.com/www.html
There are only 2 w's left at the beginning of the string, due to the offset, making it impossible for a match to be found at the first set of "www".
JavaScript's String Object has a handy function that lets you replace words that occur within the string. This comes in handy if you have a form letter with a default reference of "username". With the replace function you could grab get the person's name with an HTML form or JavaScript prompt and then replace all occurrences of "username" with the value that they entered.
String Replace Function
The string replace function has two arguments:
SearchFor - What word is going to be replaced. This can be a string or a regular expression.
ReplaceText - What the word will be replaced with. This needs to be a string.
replace returns the new string with the replaces, but if there weren't any words to replace, then the original string is returned.
Replace Function: String Replace
To start off with, let's just search for a string and replace it with the visitor's name. The first argument is what we are searching for, and the second argument is what we are going to replace.
JavaScript Code:
<script type="text/javascript">
var visitorName = "Chuck";
var myOldString = "Hello username! I hope you enjoy your stay username.";
var myNewString = myOldString.replace("username", visitorName);
document.write("Old string = " + myOldString);
document.write("<br />New string = " + myNewString);
</script>
Display:
Old string = Hello username! I hope you enjoy your stay username.
New string = Hello Chuck! I hope you enjoy your stay username.
Notice that only the first occurrence of "username" was replaced. This is the drawback to using a string as your searchFor argument. But don't worry you can replace all occurrences of "username" if you decide to use regular expressions.
Replace Function: Regular Expression
Let's do the exact same replace, except this time, we'll use a a regular expression instead of a string. The only change we need to make is to surround our searchFor word with slashes / / instead of quotations " ".
JavaScript Code:
<script type="text/javascript">
var visitorName = "Chuck";
var myOldString = "Hello username! I hope you enjoy your stay username.";
var myNewString = myOldString.replace(/username/, visitorName);
document.write("Old string = " + myOldString);
document.write("<br />New string = " + myNewString);
</script>
Display:
Old string = Hello username! I hope you enjoy your stay username.
New string = Hello Chuck! I hope you enjoy your stay username.
Darn! No luck. We've still only replaced the first "username" with Chuck instead of all of them. What's the solution to our problem? The answer is enabling the global property for our regular expression.
Replace Function: Global Regular Expression
By enabling the global property of our regular expression, we can go from replacing one match at a time to replacing all matches at once. To enable the global property, just put a "g" at the end of the regular expression.
JavaScript Code:
<script type="text/javascript">
var visitorName = "Chuck";
var myOldString = "Hello username! I hope you enjoy your stay username.";
var myNewString = myOldString.replace(/username/g, visitorName);
document.write("Old string = " + myOldString);
document.write("<br />New string = " + myNewString);
</script>
Display:
Old string = Hello username! I hope you enjoy your stay username.
New string = Hello Chuck! I hope you enjoy your stay Chuck.
Finally we've succeeded! Remember that if you just want to replace one word, you should use a string or normal regular expression as your searchFor parameter. However, if you want to replace everything, be sure to write a regular expression and append a little g at the end!
Knowing if something is or isn't in a string can be very important. If you have an online forum and don't want people to be able to create usernames that include swear words, you can use the search function to find bad words in usernames and reject them if any were found.
String Search Function
This string function takes a regular expression and then examines that string to see if there are any matches for that expression. If there is a match , it will return the position in the string where the match was found. If there isn't a match, it will return -1. We won't be going into great depth about regular expressions, but we will show you how to search for words in a string.
Search Function Regular Expression
The most important thing to remember when creating a regular expression is that it must be surrounded with slashes /regular expression/. With that knowledge let's search a string to see if a common name "Alex" is inside it.
JavaScript Code:
<script type="text/javascript">
var myRegExp = /Alex/;
var string1 = "Today John went to the store and talked with Alex.";
var matchPos1 = string1.search(myRegExp);
if(matchPos1 != -1)
document.write("There was a match at position " + matchPos1);
else
document.write("There was no match in the first string");
</script>
Display:
There was a match at position 45
Notice that our regular expression was just the name "Alex". The search function then used this name to see if "Alex" existed in string1. A match was found, and the position of the match (45), was returned.
String Search Function: Alternative Searches
Another basic tool for regular expressions is the pipe character "|" (it's below the Backspace key on standard keyboards) which allows you to search for alternative words /RegExp1|RegExp2/. Instead of just searching for just one word, we can now use the pipe character to search for multiple words.
JavaScript Code:
<script type="text/javascript">
var myRegExp = /Alex|John/;
var string1 = "Today John went to the store and talked with Alex.";
var matchPos1 = string1.search(myRegExp);
if(matchPos1 != -1)
document.write("There was a match at position " + matchPos1);
else
document.write("There was no match in the first string");
</script>
Display:
There was a match at position 6
Notice that our regular expression had two names: Alex and John. The search function then used these names to try to find the first occurrence in the string string1. John came before Alex in our string, so its position (6), was returned.
Let's look at a couple more advanced examples.
Advanced Search Function Examples
The following examples play around with the names a little so you can clearly see how the search function operates.
JavaScript Code:
<script type="text/javascript">
var myRegExp1 = /Tom|Jan|Alex/;
var string1 = "John went to the store and talked with Alexandra today.";
var matchPos1 = string1.search(myRegExp1);
if(matchPos1 != -1)
document.write("The first string found a match at " + matchPos1);
else
document.write("No match was found in the first string");
var myRegExp2 = /Tom|Jan|Alex /;
var string2 = "John went to the store and talked with Alexandra today.";
var matchPos2 = string2.search(myRegExp2);
if(matchPos2 != -1)
document.write("<br />The second string found a match at " + matchPos2);
else
document.write("<br />No match was found in the second string");
var myRegExp3 = /Tom|Jan|Alexandra/;
var string3 = "John went to the store and talked with Alexandra today.";
var matchPos3 = string3.search(myRegExp3);
if(matchPos3 != -1)
document.write("<br />The third string found a match at " + matchPos3);
else
document.write("<br />No match was found in the third string");
var myRegExp4 = /Tom|Jan|Alexandra/;
var string4 = "John went to the store and talked with Alex today.";
var matchPos4 = string4.search(myRegExp4);
if(matchPos4 != -1)
document.write("<br />The fourth string found a match at " + matchPos4);
else
document.write("<br />No match was found in the fourth string");
</script>
Display:
The first string found a match at 39
No match was found in the second string
The third string found a match at 39
No match was found in the fourth string
In the first search, a match was found. This is because our search didn't specify that the name had to be exactly Alex, and because the name Alexandra contains "Alex", a match was found.
In the second search, we fixed this by adding a space after the name Alex to make our search for "Alex ", and no match was found.
In the third search, we changed our expression to include "Alexandra" and found a match.
In the fourth and final search, we changed our string to include "Alex" and we didn't find a match.
The ability to split up a string into separate chunks has been supported in many programming languages, and it is available in JavaScript as well. If you have a long string like "Bobby Susan Tracy Jack Phil Yannis" and want to store each name separately, you can specify the space character " " and have the split function create a new chunk every time it sees a space.
Split Function: Delimiter
The space character " " we mentioned will be our delimiter and it is used by the split function as a way of breaking up the string. Every time it sees the delimiter we specified, it will create a new element in an array. The first argument of the split function is the delimiter.
Simple Split Function Example
Let's start off with a little example that takes a string of numbers and splits when it sees the number 5. That means the delimiter for this example is 5. Notice that the split function returns an array that we store into mySplitResult.
JavaScript Code:
<script type="text/javascript">
var myString = "123456789";
var mySplitResult = myString.split("5");
document.write("The first element is " + mySplitResult[0]);
document.write("<br /> The second element is " + mySplitResult[1]);
</script>
Display:
The first element is 1234
The second element is 6789
Make sure you realize that because we chose the 5 to be our delimiter, it is not in our result. This is because the delimiter is removed from the string and the remaining characters are separated by the chasm of space that the 5 used to occupy.
Larger Split Function Example
Below we have created a split example to illustrate how this function works with many splits. We have created a string with numbered words zero through four. The delimiter in this example will be the space character " ".
JavaScript Code:
<script type="text/javascript">
var myString = "zero one two three four";
var mySplitResult = myString.split(" ");
for(i = 0; i < mySplitResult.length; i++){
document.write("<br /> Element " + i + " = " + mySplitResult[i]);
}
</script>
Display:
Element 0 = zero
Element 1 = one
Element 2 = two
Element 3 = three
Element 4 = four
Advanced scripters will often need to know how long a JavaScript string is. For example, if a webdeveloper was creating a submission form that required the username to be no longer than 20 characters, then she would need to check the length of the string before allowing the user to submit data.
String Length Property
The length property returns the number of characters that are in a string, using an integer. Below is the basic code for accessing this property.
JavaScript Code:
<script type="text/javascript">
var myString = "123456";
var length = myString.length;
document.write("The string is this long: " + length);
// Same thing, but using the property inside the write function
document.write("<br />The string is this long: " + myString.length);
</script>
Display:
The string is this long: 6
The string is this long: 6
String Changed? Length Might Change
If you were to reference the length property after concatenating (adding) some characters to the string, then the length property will reflect these changes. Think of this as a friendly reminder to only check the length of the string after you are sure it isn't going to be changed.
JavaScript Code:
<script type="text/javascript">
var myString = "123456";
document.write("The string is this long: " + myString.length);
myString = myString + "7890";
document.write("<br />The string is now this long: " + myString.length);
</script>
Display:
The string is this long: 6
The string is now this long: 10
This may be old news to you, but inside every JavaScript string are several functions that are just waiting to do your bidding. This is because strings in JavaScript are actually objects with a bunch of properties and functions (also called methods) that can be accessed in the following general way:
Pseudo JavaScript Code:
<script type="text/javascript">
var myString = "Hello Thur!";
//This is how you would access a property
var myProperty = myString.property;
//This is how you would access a function
var myFunctionResult = myString.function(argument1, argument2);
</script>
As you can see, the most important part to accessing string properties and functions is to first create them. In this case, myString was our guinea pig.
What's a String Property?
A property is just some basic information about the object. For example, a string object has a length property which stores the number of characters in the string.
What's a String Function?
The string's functions are useful for finding out more about your string. For example, the string function split lets you take a string and chop it into pieces whenever characters that you supply, appear.
It is important to note that these functions do not actually change the string itself. Rather, they return new strings that you can store for use elsewhere. In our example, we stored the result of our make-believe function into myFunctionResult.
String Functions and Properties
The following lessons will teach you how to manipulate, count, reorder, replace, search and do just about anything else to your JavaScript strings. These advanced topics will open up a whole new world of choices for the dynamic webpages you have yet to build!
Hyperlinks like this one entice visitors to click because they know clicking it will lead them to a new page. However, sometimes when you are making a script, you would like to add functionality to your website that lets a hyperlink to be clicked and perform a useful action like update the sums on the webpage, without loading a new page.
It's these types of programming solutions that will utilize the JavaScript Void 0 programming tool. This lesson will teach you some of the reasons to use the JavaScript Void 0programming strategy in your scripts.
Directly Executing JavaScript in a Browser
Web browsers allow you to execute JavaScript statements directly by entering JavaScript code into the browser's URL text field. All you need to do is place a JavaScript: before your code to inform the browser you wish to run JavaScript. You can play around with this right now by typing something like
JavaScript:alert("I'm learning at Tizag.com")
into the browser's URL text field and pressing Enter.
This is useful to you, the JavaScript scripter, because you can now set your hyperlinks's href attribute equal to a JavaScript statement! This means you can remove the hyperlink's ability to load a new page and reprogram it to do your "complete some actions directly on this page" bidding.
This practice can be seen in services like Gmail (Google Email) which does a great deal of interaction with hyperlinks, but has very few new pages loading. Here is an example link that does not load a new webpage.
This is interesting to learn, but it isn't much more than a gimmick. The true power of direct URL JavaScript statements is only unleashed when you use it to return a value. This is where void 0 comes into play.
JavaScript Void 0 Explanation
Web browsers will try and take whatever is used as a URL and load it. The only reason we can use a JavaScript Alert statement without loading a new page is because alert is a function that returns a null value. This means that when the browser attempts to load a new page it sees null and has nothing to load.
The important thing to notice here is that if you ever do use a JavaScript statement as the URL that returns a value, the browser will attempt to load a page. To prevent this unwanted action, you need to use the void function on such statement, which will always return null and never load a new page.
Simple JavaScript Void 0 Simple Example
void is an operator that is used to return a null value so the browser will not be able to load a new page. An important thing to note about the void operator is that it requires a value and cannot be used by itself. Here is a simple way to use void to cancel out the page load.
JavaScript Code:
<a href="javascript: void(0)">I am a useless link</a>
This example shows how you would return a value using the void operator. myNum is a variable that we set to the value 10. We then use the same variable myNum in an alertoperation.
JavaScript Code:
<a href="javascript: void(myNum=10);alert('myNum = '+myNum)">
Set myNum Please</a>
There's nothing more troublesome than receiving orders, guestbook entries, or other form submitted data that are incomplete in some way. You can avoid these headaches once and for all with JavaScript's amazing way to combat bad form data with a technique called "form validation".
The idea behind JavaScript form validation is to provide a method to check the user entered information before they can even submit it. JavaScript also lets you display helpful alerts to inform the user what information they have entered incorrectly and how they can fix it. In this lesson we will be reviewing some basic form validation, showing you how to check for the following:
If a text input is empty or not
If a text input is all numbers
If a text input is all letters
If a text input is all alphanumeric characters (numbers & letters)
If a text input has the correct number of characters in it (useful when restricting the length of a username and/or password)
If a selection has been made from an HTML select input (the drop down selector)
If an email address is valid
How to check all above when the user has completed filling out the form
This lesson is a little long, but knowing how to implement these form validation techniques is definitely worth the effort on your part. Remember to check out Tizag's HTML forms lesson if you need to brush up on your form knowledge.
Form Validation - Checking for Non-Empty
This has to be the most common type of form validation. You want to be sure that your visitors enter data into the HTML fields you have "required" for a valid submission. Below is the JavaScript code to perform this basic check to see if a given HTML input is empty or not.
JavaScript Code:
// If the length of the element's string is 0 then display helper message
function notEmpty(elem, helperMsg){
if(elem.value.length == 0){
alert(helperMsg);
elem.focus(); // set the focus to this input
return false;
}
return true;
}
The function notEmpty will check to see that the HTML input that we send it has something in it. elem is a HTML text input that we send this function. JavaScriptstrings have built in properties, one of which is the length property which returns the length of the string. The chunk of code elem.value will grab the string inside the input and by adding on length elem.value.length we can see how long the string is.
As long as elem.value.length isn't 0 then it's not empty and we return true, otherwise we send an alert to the user with a helperMsg to inform them of their error and return false.
If someone is entering a credit card, phone number, zip code, similar information you want to be able to ensure that the input is all numbers. The quickest way to check if an input's string value is all numbers is to use a regular expression /^[0-9]+$/ that will only match if the string is all numbers and is at least one character long.
JavaScript Code:
// If the element's string matches the regular expression it is all numbers
function isNumeric(elem, helperMsg){
var numericExpression = /^[0-9]+$/;
if(elem.value.match(numericExpression)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
What we're doing here is using JavaScript existing framework to have it do all the hard work for us. Inside each string is a function called match that you can use to see if the string matches a certain regular expression. We accessed this function like so: elem.value.match(expressionhere).
We wanted to see if the input's string was all numbers so we made a regular expression to check for numbers [0-9] and stored it as numericExpression.
We then used the match function with our regular expression. If it is numeric then match will return true, making our if statement pass the test and our function isNumeric will also return true. However, if the expression fails because there is a letter or other character in our input's string then we'll display our helperMsg and return false.
This function will be identical to isNumeric except for the change to the regular expression we use inside the match function. Instead of checking for numbers we will want to check for all letters.
If we wanted to see if a string contained only letters we need to specify an expression that allows for both lowercase and uppercase letters: /^[a-zA-Z]+$/ .
JavaScript Code:
// If the element's string matches the regular expression it is all letters
function isAlphabet(elem, helperMsg){
var alphaExp = /^[a-zA-Z]+$/;
if(elem.value.match(alphaExp)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
Form Validation - Checking for Numbers and Letters
By combining both the isAlphabet and isNumeric functions into one we can check to see if a text input contains only letters and numbers.
JavaScript Code:
// If the element's string matches the regular expression it is numbers and letters
function isAlphanumeric(elem, helperMsg){
var alphaExp = /^[0-9a-zA-Z]+$/;
if(elem.value.match(alphaExp)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
Form Validation - Restricting the Length
Being able to restrict the number of characters a user can enter into a field is one of the best ways to prevent bad data. For example, if you know that the zip code field should only be 5 numbers you know that 2 numbers is not sufficient.
Below we have created a lengthRestriction function that takes a text field and two numbers. The first number is the minimum number of characters and the second is the maximum number of a characters the input can be. If you just want to specify an exact number then send the same number for both minimum and maximum.
JavaScript Code:
function lengthRestriction(elem, min, max){
var uInput = elem.value;
if(uInput.length >= min && uInput.length <= max){
return true;
}else{
alert("Please enter between " +min+ " and " +max+ " characters");
elem.focus();
return false;
}
}
Here's an example of this function for a field that requires 6 to 8 characters for a valid username.
Working Example:
<script type='text/javascript'>
function lengthRestriction(elem, min, max){
var uInput = elem.value;
if(uInput.length >= min && uInput.length <= max){
return true;
}else{
alert("Please enter between " +min+ " and " +max+ " characters");
elem.focus();
return false;
}
}
</script>
<form>
Username(6-8 characters): <input type='text' id='restrict'/>
<input type='button'
onclick="lengthRestriction(document.getElementById('restrict'), 6, 8)"
value='Check Field' />
</form>
Display:
Form Validation - Selection Made
To be sure that someone has actually selected a choice from an HTML select input you can use a simple trick of making the first option as helpful prompt to the user and a red flag to you for your validation code.
By making the first option of your select input something like "Please Choose" you can spur the user to both make a selection and allow you to check to see if the default option "Please Choose" is still selected when the submit the form.
And for our grand finale we will be showing you how to check to see if a user's email address is valid. Every email is made up for 5 parts:
A combination of letters, numbers, periods, hyphens, plus signs, and/or underscores
The at symbol @
A combination of letters, numbers, hyphens, and/or periods
A period
The top level domain (com, net, org, us, gov, ...)
Valid Examples:
bobby.jo@filltank.net
jack+jill@hill.com
the-stand@steven.king.com
Invalid Examples:
@deleted.net - no characters before the @
free!dom@bravehe.art - invalid character !
shoes@need_shining.com - underscores are not allowed in the domain name
The regular expression to check for all of this is a little overkill and beyond the scope of this tutorial to explain thoroughly. However, test it out and you'll see that it gets the job done.
JavaScript Code:
function emailValidator(elem, helperMsg){
var emailExp = /^[\w\-\.\+]+\@[a-zA-Z0-9\.\-]+\.[a-zA-z0-9]{2,4}$/;
if(elem.value.match(emailExp)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
If you've made it this far I commend you, but we're not done yet! The final step is to be able to perform all of these validation steps when the user is ready to submit their data.
Each form has a JavaScript event called onSubmit that is triggered when its submit button is clicked. If this even returns 0 or false then a form cannot be submitted, and if it returns 1 or true it will always be submitted. Wouldn't it be perfect if we could somehow make an if statement that said "If the form is valid submit it (1) else don't submit it (0)"? Well with a master formValidator function we can do just that. formValidator will be somewhat like a list of checks that we want to do before a form is submitted. But before we can decide what we want to check for, we need to have our form!
That's a lot of data to verify and the first thing we would probably want to check is that each field was at least filled out. To check for completion we will ensure no fields are empty and that the SELECT field has a selection. Here are the starting pieces of our master validation function formValidator.
JavaScript Code:
function formValidator(){
// Make quick references to our fields
var firstname = document.getElementById('firstname');
var addr = document.getElementById('addr');
var zip = document.getElementById('zip');
var state = document.getElementById('state');
var username = document.getElementById('username');
var email = document.getElementById('email');
// Check each input in the order that it appears in the form!
if(isAlphabet(firstname, "Please enter only letters for your name")){
if(isAlphanumeric(addr, "Numbers and Letters Only for Address")){
if(isNumeric(zip, "Please enter a valid zip code")){
if(madeSelection(state, "Please Choose a State")){
if(lengthRestriction(username, 6, 8)){
if(emailValidator(email, "Please enter a valid email address")){
return true;
}
}
}
}
}
}
return false;
}
The first part of this function is where we create easy references to our HTML inputs using the getElementById function. These quick references will make our next block of code much easier to read!
The second part uses a bunch of embedded if statements to see whether or not each field has the correct type of data. If every single one of those fields we check validates, then we'll return true and the form will be submitted successfully.
However, if just one of those if statements fails then the return false at the end of the function is reached and prevents the form for being submitted.
As you can see this function really does do quite a lot, definitely earning the title of formValidator. Notice how this one function references all of the functions we have covered in this lesson. By placing all of these checks in a central location you make your code easier to read and easier to change around in the future.
Now let's put all the necessary and HTML together and try it out!
All Together Now
Below we have taken the HTML form code and the new function formValidator and plugged in all the other form validation functions taught in this lesson that are referenced in formValidator.
HTML & JavaScript Code:
<script type='text/javascript'>
function formValidator(){
// Make quick references to our fields
var firstname = document.getElementById('firstname');
var addr = document.getElementById('addr');
var zip = document.getElementById('zip');
var state = document.getElementById('state');
var username = document.getElementById('username');
var email = document.getElementById('email');
// Check each input in the order that it appears in the form!
if(isAlphabet(firstname, "Please enter only letters for your name")){
if(isAlphanumeric(addr, "Numbers and Letters Only for Address")){
if(isNumeric(zip, "Please enter a valid zip code")){
if(madeSelection(state, "Please Choose a State")){
if(lengthRestriction(username, 6, 8)){
if(emailValidator(email, "Please enter a valid email address")){
return true;
}
}
}
}
}
}
return false;
}
function notEmpty(elem, helperMsg){
if(elem.value.length == 0){
alert(helperMsg);
elem.focus(); // set the focus to this input
return false;
}
return true;
}
function isNumeric(elem, helperMsg){
var numericExpression = /^[0-9]+$/;
if(elem.value.match(numericExpression)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
function isAlphabet(elem, helperMsg){
var alphaExp = /^[a-zA-Z]+$/;
if(elem.value.match(alphaExp)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
function isAlphanumeric(elem, helperMsg){
var alphaExp = /^[0-9a-zA-Z]+$/;
if(elem.value.match(alphaExp)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
function lengthRestriction(elem, min, max){
var uInput = elem.value;
if(uInput.length >= min && uInput.length <= max){
return true;
}else{
alert("Please enter between " +min+ " and " +max+ " characters");
elem.focus();
return false;
}
}
function madeSelection(elem, helperMsg){
if(elem.value == "Please Choose"){
alert(helperMsg);
elem.focus();
return false;
}else{
return true;
}
}
function emailValidator(elem, helperMsg){
var emailExp = /^[\w\-\.\+]+\@[a-zA-Z0-9\.\-]+\.[a-zA-z0-9]{2,4}$/;
if(elem.value.match(emailExp)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
</script>
<form onsubmit='return formValidator()' >
First Name: <input type='text' id='firstname' /><br />
Address: <input type='text' id='addr' /><br />
Zip Code: <input type='text' id='zip' /><br />
State: <select id='state'>
<option>Please Choose</option>
<option>AL</option>
<option>CA</option>
<option>TX</option>
<option>WI</option>
</select><br />
Username(6-8 characters): <input type='text' id='username' /><br />
Email: <input type='text' id='email' /><br />
<input type='submit' value='Check Form' />
</form>
Display:
First Name:
Address:
Zip Code:
State:
Username(6-8 characters):
Email:
The Date object is useful when you want to display a date or use a timestamp in some sort of calculation. In Java, you can either make a Date object by supplying the date of your choice, or you can let JavaScript create a Date object based on your visitor's system clock. It is usually best to let JavaScript simply use the system clock.
When creating a Date object based on the computer's (not web server's!) internal clock, it is important to note that if someone's clock is off by a few hours or they are in a different time zone, then the Date object will create a different times from the one created on your own computer.
JavaScript Date Today (Current)
To warm up our JavaScript Date object skills, let's do something easy. If you do not supply any arguments to the Date constructor (this makes the Date object) then it will create a Date object based on the visitor's internal clock.
HTML & JavaScript Code:
<h4>It is now
<script type="text/javascript">
<!--
var currentTime = new Date()
//-->
</script>
</h4>
Display:
It is now
Nothing shows up! That's because we still don't know the methods of the Date object that let us get the information we need (i.e. Day, Month, Hour, etc).
Get the JavaScript Time
The Date object has been created, and now we have a variable that holds the current date! To get the information we need to print out, we have to utilize some or all of the following functions:
getTime() - Number of milliseconds since 1/1/1970 @ 12:00 AM
getSeconds() - Number of seconds (0-59)
getMinutes() - Number of minutes (0-59)
getHours() - Number of hours (0-23)
getDay() - Day of the week(0-6). 0 = Sunday, ... , 6 = Saturday
getDate() - Day of the month (0-31)
getMonth() - Number of month (0-11)
getFullYear() - The four digit year (1970-9999)
Now we can print out the date information. We will be using the getDate, getMonth, and getFullYear methods in this example.
HTML & JavaScript Code:
<h4>It is now
<script type="text/javascript">
<!--
var currentTime = new Date()
var month = currentTime.getMonth() + 1
var day = currentTime.getDate()
var year = currentTime.getFullYear()
document.write(month + "/" + day + "/" + year)
//-->
</script>
</h4>
Display:
It is now 11/21/2011 !
Notice that we added 1 to the month variable to correct the problem with January being 0 and December being 11. After adding 1, January will be 1, and December will be 12.
JavaScript Current Time Clock
Now, instead of displaying the date we, will display the format you might see on a typical digital clock -- HH:MM AM/PM (H = Hour, M = Minute).
HTML & JavaScript Code:
<h4>It is now
<script type="text/javascript">
<!--
var currentTime = new Date()
var hours = currentTime.getHours()
var minutes = currentTime.getMinutes()
if (minutes < 10){
minutes = "0" + minutes
}
document.write(hours + ":" + minutes + " ")
if(hours > 11){
document.write("PM")
} else {
document.write("AM")
}
//-->
</script>
</h4>
Display:
It is now 14:41 PM
Above, we check to see if either the hours or minutes variable is less than 10. If it is, then we need to add a zero to the beginning of minutes. This is not necessary, but if it is 1:01 AM, our clock would output "1:1 AM", which doesn't look very nice at all!
Chances are, if you are reading this webpage, then you have experienced hundreds of JavaScript popup windows throughout your web surfing lifetime. Want to dish out some pain of your own creation onto unsuspecting visitors? I hope not! Because websites with irrelevant popups are bad!
However, we will show you how to make windows popup for reasonable occasions, like when you want to display extra information, or when you want to have something open a new window that isn't an HTML anchor tag (i.e. a hyperlink).
JavaScript window.open Function
The window.open() function creates a new browser window, customized to your specifications, without the use of an HTML anchor tag. In this example, we will be making a function that utilizes the window.open() function.
This works with pretty much any tag that can be clicked on, so please go ahead and experiment with this fun little tool. Afterwards, read on to learn more about the different ways you can customize the JavaScript window that pops up.
JavaScript Window.Open Arguments
There are three arguments that the window.open function takes:
The relative or absolute URL of the webpage to be opened.
The text name for the window.
A long string that contains all the different properties of the window.
Naming a window is very useful if you want to manipulate it later with JavaScript. However, this is beyond the scope of this lesson, and we will instead be focusing on the different properties you can set with your brand spanking new JavaScript window. Below are some of the more important properties:
dependent - Subwindow closes if the parent window (the window that opened it) closes
fullscreen - Display browser in fullscreen mode
height - The height of the new window, in pixels
width - The width of the new window, in pixels
left - Pixel offset from the left side of the screen
top - Pixel offset from the top of the screen
resizable - Allow the user to resize the window or prevent the user from resizing, currently broken in Firefox.
status - Display or don't display the status bar
Dependent, fullscreen, resizable, and status are all examples of ON/OFF properties. You can either set them equal to zero to turn them off, or set them to one to turn them ON. There is no inbetween setting for these types of properties.
Upgraded JavaScript Popup Window!
Now that we have the tools, let's make a sophisticated JavaScript popup window that we can be proud of!
Now, that is a prime example of a worthless popup! When you make your own, try to have them relate to your content, like a small popup with no navigation that just gives the definition or explanation of a word, sentence, or picture!
You're moving to a new domain name. You have a time-delay placeholder on your download site. You have a list of external web servers that are helping to mirror your site. What will help you deal with and/or take advantage of these situations? JavaScript redirects will.
When your webpage is moved, you'd probably want to notify your visitors of the change. One good way is to place a "redirect page" at the old location which, after a timed delay, will forward visitors to the new location of your webpage. You can do just this with a JavaScript redirection.
JavaScript Window.Location
Control over what page is loaded into the browser rests in the JavaScript property window.location. By setting window.location equal to a new URL, you will in turn change the current webpage to the one that is specified. If you wanted to redirect all your visitors to www.google.com when they arrived at your site, you would just need the script below:
Implementing a timed delay in JavaScript is useful in the following situations:
Showing an "Update your bookmark" page when you have to change URLs or page locations
For download sites that wish to have a timed delay before the download starts
To refresh a webpage once every specified number of seconds
The code for this timed delay is slightly involved and is beyond the scope of this tutorial. However, we have tested it and it seems to function properly.
HTML & JavaScript Code:
<html>
<head>
<script type="text/javascript">
<!--
function delayer(){
window.location = "../javascriptredirect.php"
}
//-->
</script>
</head>
<body onLoad="setTimeout('delayer()', 5000)">
<h2>Prepare to be redirected!</h2>
<p>This page is a time delay redirect, please update your bookmarks to our new
location!</p>
</body>
</html>
The most important part of getting the delay to work is being sure to use the JavaScript function setTimeout. We want the delayer() function to be used after 5 seconds or 5000 milliseconds (5 seconds), so we pass the setTimeout() two arguments.
'delayer()' - The function we want setTimeout() to execute after the specified delay.
5000 - the number of millisecods we want setTimeout() to wait before executing our function. 1000 miliseconds = 1 second.
Web Page Redirection
Do use JavaScript for redirections when you change your website's URL or move a file to a new location. Don't use redirections when they can easily be replaced with a normal HTML hyperlink.
The JavaScript print function performs the same operation as the print option that you see at the top of your browser window or in your browser's "File" menu. The JavaScript print function will send the contents of the webpage to the user's printer.
Many believe this function to be worthless, but there are many computer users who do not know their way around a computer well, and helpful features such as this function can somtimes create a more user-friendly environment.
JavaScript Print Script - window.print()
The JavaScript print function window.print() will print the current webpage when executed. In this example script, we will be placing the function on a JavaScript button that will perform the print operation when the onClick event occurs.
HTML & JavaScript Code:
<form>
<input type="button" value="Print This Page" onClick="window.print()" />
</form>
Display:
If you click this button you should be prompted with whatever application your computer uses to handle its print functionality.
The JavaScript prompt is a relic from the 1990's that you seldom see being used in modern day websites. The point of the JavaScript prompt is to gather information from the user so that the information can be used throughout the site to give the visitor a personalized feel.
Back in the day, you'd often see prompts on personal webpages asking for your name. After you typed in the information, you would be greeted with a page that had a welcome message, such as, "Welcome to My Personal WebPage John Schmieger!" (If your name just so happened to be John Schmieger).
The JavaScript prompt is not very useful and many find it slightly annoying, but hey, this tutorial is here to educate you, so let's learn how to make that prompt!
Simple JavaScript Prompt
You can use a prompt for a wide variety of useless tasks, but below we use it for an exceptionally silly task. Our prompt is used to gather the user's name to be displayed in our alert dialogue box.
HTML & JavaScript Code:
<head>
<script type="text/javascript">
<!--
function prompter() {
var reply = prompt("Hey there, good looking stranger! What's your name?", "")
alert ( "Nice to see you around these parts " + reply + "!")
}
//-->
</script>
</head>
<body>
<input type="button" onclick="prompter()" value="Say my name!">
</body>
Display:
Recap on JavaScript Prompt
It sure is a quick way to gather some information, but it is not as reliable an information gatherer as other options available to you. If you want to find out someone's name and information, the best way to request this information would be through the use of HTML Forms. And if you want to use the information you collected in your website, you might use some PHP to get that job done in a more sophisticated manner.
The JavaScript confirm function is very similar to the JavaScript alert function. A small dialogue box pops up and appears in front of the web page currently in focus. The confirm box is different from the alert box. It supplies the user with a choice; they can either press OK to confirm the popup's message or they can press cancel and not agree to the popup's request.
Confirmation are most often used to confirm an important actions that are taking place on a website. For example, they may be used to confirm an order submission or notify visitors that a link they clicked will take them to another website.
JavaScript Confirm Example
Below is an example of how you would use a confirm dialogue box to warn users about something, giving them the option to either continue on or stay put.
Note the part in red. This is where all the magic happens. We call the confirm function with the message, "Leave Tizag?". JavaScript then makes a popup window with two choices and will return a value to our script code depending on which button the user clicks.
If the user clicks OK, a value of 1 is returned. If a user clicks cancel, a value of 0 is returned.. We store this value in answer by setting it equal to the confirm function call.
After answer has stored the value, we then use answer as a conditional statement. If answer is anything but zero, then we will send the user away from Tizag.com. If answer is equal to zero, we will keep the user at Tizag.com because they clicked the Cancel button.
In either case, we have a JavaScript alert box that appears to inform the user on what is going to happen. It will say, "Bye bye!" if they choose to leave and, "Thanks for sticking around!" if they choose to stay.
In this lesson, we also used the window.location property for the first time. Whatever we set window.location to will be where the browser is redirected to. In this example, we chose Google.com. We will discuss redirection in greater detail later on.
If you do not have JavaScript enabled on your web browser, then you may have been able to avoid "alerts" in your internet adventures. The JavaScript alert is a dialogue box that pops up and takes the focus away from the current window and forces the web browser to read the message. View an alert message.
You may have noticed that you didn't get a JavaScript alert popup when you came to this page. That is because doing so would be in bad taste for a web designer. You see, alerts should be very, very rarely used and even then these following guidelines should be considered when using them.
When to Use Popups / Alerts
JavaScript alerts are ideal for the following situations:
If you want to be absolutely sure they see a message before doing anything on the website.
You would like to warn the user about something. For example "the following page contains humor not suitable for those under the age of 14."
An error has occurred and you want to inform the user of the problem.
When asking users for confirmation of some action. For example, if they have just agreed to sign over the deed to their house and you want to ask them again if they are absolutely positive they want to go through with this decision!
Even though the above situations would all be valid times to use the alert function, you could also skip the alert popup and just have the error message, confirmation, etc displayed in plain HTML. More and more bigger sites are opting to lose JavaScript alerts and instead keep everything in HTML.
Coding a Simple JavaScript Alert
Just for fun, let's suppose that we are making an alert for some website that asks people to hand over the deed to their house. We need to add an alert to be sure these people are in agreement. The following code will add an alert by using an HTML button and the onClick event.
HTML & JavaScript Code:
<form>
<input type="button" onclick=
"alert('Are you sure you want to give us the deed to your house?')"
value="Confirmation Alert">
</form>
Display:
The string that appears between the single quotes is what will be printed inside the alert box when the user clicks on the button. If the HTML Forms are confusing to you, be sure to brush up on our HTML Forms Lesson. Continue the tutorial to learn more about the different kinds of JavaScript pop ups that are at your disposal.
An array is a variable that can store many variables within it. Many programmers have seen arrays in other languages, and they aren't that different in JavaScript.
The following points should always be remembered when using arrays in JavaScript:
The array is a special type of variable.
Values are stored into an array by using the array name and by stating the location in the array you wish to store the value in brackets. Example: myArray[2] = "Hello World";
Values in an array are accessed by the array name and location of the value. Example: myArray[2];
JavaScript has built-in functions for arrays, so check out these built-in array functions before writing the code yourself!
Creating a JavaScript Array
Creating an array is slightly different from creating a normal variable. Because JavaScript has variables and properties associated with arrays, you have to use a special function to create a new array. This example shows how you would create a simple array, store values to it, and access these values.
Notice that you set values and get values from an array by specifying the position, in brackets, of the value you want to use.
JavaScript Array Sorting
Imagine that you wanted to sort an array alphabetically before you wrote the array to the browser. Well, this code has already been written and can be accessed by using the Array's sort method.
Arrays are a very complex area of programming, especially in JavaScript. This lesson cannot possibly cover all the areas of JavaScript arrays, but we have compiled some useful resources for you to check out!
Have you ever written a script or a program in the past only to look at it six months later with no idea what's going on in the code? You probably forgot to do what all programmers tend to forget to do: write comments!
When writing code you may have some complex logic that is confusing, this is a perfect opportunity to include some comments in the code that will explain what is going on. Not only will this help you remember it later on, but if you someone else views your code, they will also be able to understand the code (hopefully)!
Another great thing about comments is the ability for comments to remove bits of code from execution when you are debugging your scripts. This lesson will teach you how to create two types of comments in JavaScript: single line comments and multi-line comments.
Creating Single Line Comments
To create a single line comment in JavaScript, you place two slashes "//" in front of the code or text you wish to have the JavaScript interpreter ignore. When you place these two slashes, all text to the right of them will be ignored, until the next line.
These types of comments are great for commenting out single lines of code and writing small notes.
JavaScript Code:
<script type="text/javascript">
<!--
// This is a single line JavaScript comment
document.write("I have comments in my JavaScript code!");
//document.write("You can't see this!");//-->
</script>
Display:
I have comments in my JavaScript code!
Each line of code that is colored red is commented out and will not be interpreted by the JavaScript engine.
Creating Multi-line Comments
Although a single line comment is quite useful, it can sometimes be burdensome to use when disabling long segments of code or inserting long-winded comments. For this large comments you can use JavaScript's multi-line comment that begins with /* and ends with */.
JavaScript Code:
<script type="text/javascript">
<!--
document.write("I have multi-line comments!");
/*document.write("You can't see this!");
document.write("You can't see this!");
document.write("You can't see this!");
document.write("You can't see this!");
document.write("You can't see this!");
document.write("You can't see this!");
document.write("You can't see this!");*/
//-->
</script>
Display:
I have multi-line comments!
Quite often text editors have the ability to comment out many lines of code with a simple key stroke or option in the menu. If you are using a specialized text editor for programming, be sure that you check and see if it has an option to easily comment out many lines of code!
