PROWAREtech

articles » current » javascript » tutorial » page-01

JavaScript: Tutorial - A Guide to JavaScript - Page 01

Interesting Facts, JavaScript in HTML.

Some Interesting Things About JavaScript

In JavaScript, functions are objects. They can be passed as arguments and be used as return values.

JavaScript is a prototype-based language. Object-oriented programming languages fall into one of two categories. There are class-based languages, like Visual Basic.NET, C# and Java, and prototype-based languages, like JavaScript. Prototype-based languages don't instantiate a new object on the basis of a class definition. They construct a new object by cloning the object's prototype.

JavaScript in HTML

The <script> Element

There are two ways to use the <script> element. One, embed JavaScript code directly into the document or, two, include JavaScript from an external file. To include inline JavaScript code, place JavaScript code inside the <script> element directly:

<script type="text/javascript">
	function hello() {
		alert("Hello, World!");
	}
	hello();
</script>

The JavaScript code contained inside a <script> element is interpreted from top to bottom. The rest of the document content is not loaded and/or displayed until after all of the code inside the <script> element has been evaluated.

Before the modern browsers of today, it was neccessary to enclose the JavaScript in comment tags to prevent browsers that do not support the <script> tag from displaying the JavaScript code in the document. Though it may still work, this is no longer needed. The following is an example of this:

<script type="text/javascript"><!--
	function hello() {
		alert("Hello, World!");
	}
	hello();
// --></script>

When utilizing inline JavaScript code, one can not have the string "</script>" anywhere in your code. The following code causes an error when loaded:

<script type="text/javascript">
	function sayScript(){
		alert("</script>");
	}
	sayScript();
</script>

The browser sees the string "</script>" as if it were the closing </script> tag, but this problem can be easily avoided by escaping the "/" character:

<script type="text/javascript">
	function sayScript(){
		alert("<\/script>");
	}
	sayScript();
</script>

The src attribute is required to include JavaScript from an external file. The value of src is a URI linked to a file containing JavaScript code:

<script type="text/javascript" src="example.js"></script>

An external file named example.js is loaded into the document in this example. The file itself need only contain the JavaScript code that would occur between the opening <script> and closing </script> tags. Processing of the document is halted until the external file is interpreted. There is also time taken to download it. One can omit the closing tag in XHTML documents:

<script type="text/javascript" src="example.js" />

Because it is invalid HTML and won't be handled properly by some browsers, this syntax should not be used in HTML documents.

Much like an <img> element, the <script> element's src attribute may be set to a full URI that exists outside the domain on which the HTML document exists.

<<<[Page 1 of 22]>>>

This site uses cookies. Cookies are simple text files stored on the user's computer. They are used for adding features and security to this site. Read the privacy policy.
CLOSE