Full documentation of Javascript can be found at Mozilla Developer Center

Using javascript in HTML

To include javascript in an HTML document, enclose the script within a <script> tag with type attribute of 'text/javascript'. In the interests of keeping content and behaviour seperate, and to meet the stricter specifications of XHTML, place your javascript in an external file and link to it in the header of your XHTML

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

Hello World

Several functions exist to prompt for a user response:

• alert('myMessage') - pops up a message with an 'OK' button
• confirm('myMessage') - pops up a message with 'OK' and 'Cancel' buttons
• prompt(myMessage, myDefault) - prompts for user input, with optional default value

The write() function of the document object allows us to insert HTML into the page, and is useful for debugging (displaying values of variables for instance), as are alert and confirm. Document.write adds a string to the document and the script must therefore be placed within the HTML file.

<script type="text/Javascript">
//One line comments begin with two forward slashes

/*
Multiline comments begin 
as above and end as below
*/

//alert produces a pop-up box
alert("Hello World");
//document write inserts text into document
document.write('<p>Hello World</p>');
</script>

Variables

There are six basic variable types:

1. Numbers
2. Strings
3. Booleans
4. Arrays
5. Functions
6. Objects

Variables should be declared with the 'var' keyword unless you want a global variable

var myString = 'This will be saved for later';
var myCopyString = myString;
myString = prompt('Please enter some text');
var myArray = new Array("Dave Dee", "Dozy", "Beaky", "Mick" and "Twit");
myArray[4] = "Tich";
var myHashArray = new Array();
myHashArray('good') = 'Linux';
myHashArray('bad') = 'SCO Unix';
myHashArray('ugly') = 'Windows';

Operators

Mathematical

Comparison

Logical

Objects

Unlike simple data types, objects come with methods and properties

String Objects

Declaring a string object:

var stringObject = new String('Not a simply a string. Has methods and properties.')

String Object methods:

Date Objects

Declaring a date object:

var todayObject = new Date('');
var otherDateObject = new Date(myYear, myMonth, myMonthDate, myHour, myMinutes, mySeconds);
var anotherDateObject = new Date("14 May 1964"); 

Math Objects

Array Objects

Declaring an array object:

var myArray = new Array('Yes', 'No', 'OK', 'Maybe');

Conditional Statements

If

if (condition) {
	//do something
}
else {
	//do something else
}

Switch

switch(condition) {
	case conditionOne:
	//code to execute 
	break; 
	case conditionTwo:
	//code to execute
	break; 
	case conditionThree:
	//code to execute
	break;
	default:
	//code to execute if no conditions match
}

'break' can also be used to prematurely terminate nested ifs

For

for (initial-condition; loop-test; increment) {
	//code to execute
}

for (index in array) {
	//code to execute
}

While

while (condition) {//code to execute}

'continue' can be used to terminate the remainder of a block and continue the loop at the next iteration

The do..while guarantees the code will execute at least once

do {//code to execute} while (condition)

The ternary operator

var variable = condition ? trueValue:falseValue;

String Conversion

String object methods can be used on simple string variables: an implicit conversion is performed, but the variable remains a string variable not a string object. Use typeof(myVar) to determine the type of a variable. Several methods exist to make an explicit conversion of a string variable:

• parseFloat(userVar)
• parseInt(userVar)
• Number(userVar)