Introducing JavaScript

Vineet Kumar Saini
Nov 06, 2011
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Introduction

JavaScript is a kind of scripting language. Scripting Languages are used to put logic with HTML tags. They are small languages, having no environment. It is executed in browser with HTML.

All the scripting languages are Interpreted languages. There are some script languages, which are as follows:

java Script :- Netscape
Jscript :- MS (C/c++/java/c#)
Vbscript :- MS (vb)

Why we use JavaScript

It is mainly used for Client side validations.

Fundamentals Of JavaScript

There are no any specific data type (e.g. :-var t) in JavaScript.
There are if, for, switch, while, do while, break, continue same as java or c# in JavaScript.
document.write() is used for display output in JavaScript.
There are some dialogues in JavaScript, which are as follows
Alert -- Ok
Confirm -- Ok/CANCEL
Prompt -- Input
Function :-There are 'function' keyword used for function in JavaScript.

Some Examples of JavaScript:

Simple program of JavaScript.

<html>
<head>
<title>MY TITLE</title>
</head>
<body>
<script type="text/javascript">
document.write("Most Welcome in JavaScript")
</script>
</body>
</html>

Output

If-else program in JavaScript.

<html>
<body>
<script type="text/javascript">
    var d = new Date()
    var time = d.getHours()
    if (time < 10) {
        document.write("<b>Good morning</b>")
    }
    else {
        document.write("<b>Good day</b>")
    }
</script>
<p>
This example demonstrates the If...Else statement.
</p>
<p>
If the time on your browser is less than 10,
you will get a "Good morning" greeting.
Otherwise you will get a "Good day" greeting.
</p>
</html>

Output

Switch case in JavaScript.

<html>
<body>
<script type="text/javascript">
    var d = new Date()
    theDay = d.getDay()
    switch (theDay) {
        case 5:
            document.write("<b>Finally Friday</b>")
            break
        case 6:
            document.write("<b>Super Saturday</b>")
            break
        case 0:
            document.write("<b>Sleepy Sunday</b>")
            break
        default:
            document.write("<b>I'm really looking forward to this weekend!</b>")
    }
</script>
<p>This JavaScript will generate a different greeting based on what day it is. Note that Sunday=0, Monday=1, Tuesday=2, etc.</p>
</body>
</html>

Output

For loop in JavaScript.

<html>
<body>
<script type="text/javascript">
    for (i = 0; i <= 5; i++) {
        document.write("The number is " + i)
        document.write("<br />")
    }
</script>
<p>Explanation:</p>
<p>This for loop starts with i=0.</p>
<p>As long as <b>i</b> is less than, or equal to 5, the loop will continue to run.</p>
<p><b>i</b> will increase by 1 each time the loop runs.</p>
</body>
</html>

Output

While loop in JavaScript.

<html>
<body>
<script type="text/javascript">
    var i = 0;
    while(i <= 5){
        document.write("The number is " + i)
        document.write("<br />")
        i++
    }
</script>
<p>Explanation:</p>
<p>This while loop starts with i=0.</p>
<p>As long as <b>i</b> is less than, or equal to 5, the loop will continue to run.</p>
<p><b>i</b> will increase by 1 each time the loop runs.</p>
</body>
</html>

Output

Do-while loop in JavaScript.

<html>
<<body>
<script type="text/javascript">
    var i = 0;
    do {
        i++;
        document.write("The number is " + i)
        document.write("<br />")
    }while(i<=5)
</script>
<p>Explanation:</p>
<p>This do-while loop starts with i=0.</p>
<p>As long as <b>i</b> is less than, or equal to 5, the loop will continue to run.</p>
<p><b>i</b> will increase by 1 each time the loop runs.</p>
</body>
</html>

Output

Break statement in JavaScript.

Output

Continue statement in JavaScript.

Output

Function in JavaScript.

<html>
<head>
<script type="text/javascript">
    function product(a, b) {
        return a * b
    }
</script>
</head>
<body>
<script type="text/javascript">
    document.write(product(4, 3))
</script>
<p>The script in the body section calls a function with two parameters (4 and 3).</p>
<p>The function will return the product of these two parameters.</p>
</body>
</html>