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JS Tutorial

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JS Forms

JS Forms Forms API

JS Objects

Object Definitions Object Properties Object Methods Object Prototypes

JS Functions

Function Definitions Function Parameters Function Invocation Function Closures

JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML DOM CSS DOM Animations DOM Events DOM EventListener DOM Navigation DOM Nodes DOM Nodelist

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JS AJAX

AJAX Intro AJAX XMLHttp AJAX Request AJAX Response AJAX XML File AJAX PHP AJAX ASP AJAX Database AJAX Applications AJAX Examples

JS JSON

JSON Intro JSON Syntax JSON vs XML JSON Data Types JSON Objects JSON Arrays JSON Parse JSON Stringify JSON PHP JSON HTML JSON JSONP

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser JS Quiz JS Certificate

JS References

JavaScript Objects HTML DOM Objects


JavaScript Where To


The <script> Tag

In HTML, JavaScript code must be inserted between <script> and </script> tags.

Example

<script>
document.getElementById("demo").innerHTML = "My First JavaScript";
</script>

Try it Yourself »

Old JavaScript examples may use a type attribute: <script type="text/javascript">.
The type attribute is not required. JavaScript is the default scripting language in HTML.


JavaScript Functions and Events

A JavaScript function is a block of JavaScript code, that can be executed when "called" for.

For example, a function can be called when an event occurs, like when the user clicks a button.

You will learn much more about functions and events in later chapters.


JavaScript in <head> or <body>

You can place any number of scripts in an HTML document.

Scripts can be placed in the <body>, or in the <head> section of an HTML page, or in both.


JavaScript in <head>

In this example, a JavaScript function is placed in the <head> section of an HTML page.

The function is invoked (called) when a button is clicked:

Example

<!DOCTYPE html>
<html>

<head>
<script>
function myFunction() {
    document.getElementById("demo").innerHTML = "Paragraph changed.";
}
</script>
</head>

<body>

<h1>A Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try it</button>

</body>
</html>

Try it Yourself »

JavaScript in <body>

In this example, a JavaScript function is placed in the <body> section of an HTML page.

The function is invoked (called) when a button is clicked:

Example

<!DOCTYPE html>
<html>
<body>

<h1>A Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try it</button>

<script>
function myFunction() {
   document.getElementById("demo").innerHTML = "Paragraph changed.";
}
</script>

</body>
</html>
Try it Yourself »

Placing scripts at the bottom of the <body> element improves the display speed, because script compilation slows down the display.


External JavaScript

Scripts can also be placed in external files:

External file: myScript.js

function myFunction() {
   document.getElementById("demo").innerHTML = "Paragraph changed.";
}

External scripts are practical when the same code is used in many different web pages.

JavaScript files have the file extension .js.

To use an external script, put the name of the script file in the src (source) attribute of a <script> tag:

Example

<!DOCTYPE html>
<html>
<body>

<script src="myScript.js"></script>

</body>
</html>
Try it Yourself »

You can place an external script reference in <head> or <body> as you like.

The script will behave as if it was located exactly where the <script> tag is located.

External scripts cannot contain <script> tags.


External JavaScript Advantages

Placing scripts in external files has some advantages:

  • It separates HTML and code
  • It makes HTML and JavaScript easier to read and maintain
  • Cached JavaScript files can speed up page loads

To add several script files to one page  - use several script tags:

Example

<script src="myScript1.js"></script>
<script src="myScript2.js"></script>

External References

External scripts can be referenced with a full URL or with a path relative to the current web page.

This example uses a full URL to link to a script:

Example

<script src="http://www.w3schools.com/js/myScript1.js"></script>

Try it Yourself »

This example uses a script located in a specified folder on the current web site:

Example

<script src="/js/myScript1.js"></script>

Try it Yourself »

This example links to a script located in the same folder as the current page:

Example

<script src="myScript1.js"></script>

Try it Yourself »

You can read more about file paths in the chapter HTML File Paths.