JavaScript Where To ...

Scripts in the body section will execute while the page loads.

Scripts in the head section will be executed when called.

Examples

Head section
Scripts that contain functions go in the head section of the document. Then we can be sure that the script is loaded before the function is called.

Body section
Execute a script that is placed in the body section.

External script
How to access an external script.

Where to Put the JavaScript

Scripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, other times when a user triggers an event.

Scripts in the head section: Scripts to be executed when they are called, or when an event is triggered, go in the head section. When you place a script in the head section, you will ensure that the script is loaded before anyone uses it.

<html>
<head>
<script type="text/javascript">
     some statements
</script>
</head>

Scripts in the body section: Scripts to be executed when the page loads go in the body section. When you place a script in the body section it generates the content of the page.

<html>
<head>
</head>
<body>
<script type="text/javascript">
     some statements
</script>
</body>

Scripts in both the body and the head section: You can place an unlimited number of scripts in your document, so you can have scripts in both the body and the head section.

<html>
<head>
<script type="text/javascript">
     some statements
</script>
</head>
<body>
<script type="text/javascript">
     some statements
</script>
</body>

How to Run an External JavaScript

Sometimes you might want to run the same script on several pages, without writing the script on each and every page.

To simplify this you can write a script in an external file, and save it with a .js file extension, like this:

document.write("This script is external")

Save the external file as xxx.js.

Note: The external script cannot contain the <script> tag

Now you can call this script, using the "src" attribute, from any of your pages:

<html>
<head>
</head>
<body>
<script src="xxx.js"></script>
</body>
</html>

Remember to place the script exactly where you normally would write the script.

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