Published by Admin on 17 Oct 2007
JavaScript Where To …
JavaScripts in the body section will be executed WHILE the page loads.
JavaScripts in the head section will be executed when CALLED.
Examples
Head section
<html>
<head>
<script type=”text/javascript”>
function message()
{
alert(“This alert box was called with the onload event”)
}
</script>
</head><body onload=”message()”>
</body>
</html>
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
<html>
<head>
</head><body>
<script type=”text/javascript”>
document.write(“This message is written when the page loads”)
</script></body>
</html>
Execute a script that is placed in the body section.
External script
<html>
<head>
</head>
<body><script src=”xxx.js”>
</script><p>
The actual script is in an external script file called “xxx.js”.
</p></body>
</html>
How to access an external script.
Where to Put the JavaScript
JavaScripts 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”>
….
</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”>
….
</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”>
….
</script>
</head>
<body>
<script type=”text/javascript”>
….
</script>
</body>
Using an External JavaScript
Sometimes you might want to run the same JavaScript on several pages, without having to write the same script on every page.
To simplify this, you can write a JavaScript in an external file. Save the external JavaScript file with a .js file extension.
Note: The external script cannot contain the <script> tag!
To use the external script, point to the .js file in the “src” attribute of the <script> tag:
<html>
<head>
<script src=”xxx.js”></script>
</head>
<body>
</body>
</html>
Note: Remember to place the script exactly where you normally would write the script!
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