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JavaScript Where To


JavaScript can be placed in the <body> and the <head> sections of an HTML page.


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>

JavaScript Functions and Events

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

For example, a function can be executed 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>My 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>My 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 »

External JavaScript

Scripts can also be placed in external files.

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 the <script> tag:

Example

<!DOCTYPE html>
<html>
<body>
<script src="myScript.js"></script>
</body>
</html>
Try it yourself »

External JavaScript Advantages

Placing JavaScripts 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