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A Simple Example 1 -- Hello World

The script that follows could hardly be easier. We'll list the code first then explain what's going on.

<html>
 <head>
   <title> Hello World JavaScript</title>
 </head>

<body >
<script language="javascript">
 
   var str = "Hello World";

   window.alert(str);
 
   document.write("<h1>" + str + "</h1>");
 
</script>


</body>
</html>

The key points of JavaScript Programs:

The JavaScript program is contained between the <script> .... </script>
The language attribute must be set to "javascript" i.e
```
<script language="javascript">
```
JavaScript programs contain variables, objects and functions.
Each line of code is terminated by a semi-colon;
Blocks of code must be surrounded by a pair of curly brackets. A block of code is a set of instructions that are to be executed together as a unit. This might be because they are optional and dependent upon a boolean condition or because they are to be executed repeatedly;
Functions have parameters which are passed inside parenthesis;
Variables are declared using the keyword var;
Scripts require neither a main function nor an exit condition.
Functions may be used.

Specifically for the Hello World Program:

We create a variable str and store the string "Hello World" in it.
We create an alert window with the message "Hello World". The window object is used and we call the alert method (function) of this object.

Figure: Hello World JavaScript Example
We write() to the document model some HTML.

Next: A Simple Example 1 Up: First Steps in JavaScript Previous: Running Javascript

Dave Marshall
9/28/2001