Functions in JavaScript

A function is a sequence of reusable code that can be called anywhere in a program.

This eliminates the need to repeat the same code.

Functions are a central working unit of JavaScript.

The most common way to define a function in JavaScript is by using the function keyword, followed by a unique function name, a list of parameters (that might be empty), and a statement block surrounded by curly braces.

Syntax:

<script type="text/javascript">
<!--
function functionname(parameter-list)
{
 Statements
}
//-->
</script>


1. Function with no parameter

 

<script type="text/javascript">|
<!--
function abhijeet()
{
alert("hello guyzz");
}
//-->
</script>


Calling a Function:

 

<script type="text/javascript">
<!--
abhijeet();
//-->
</script>

Function with Parameters

<script type="text/javascript">
<!--
function abhijeet(name, age)
{
alert( name + " is " + age + " years old.");
}
//-->
</script>

Calling a Function:

<script type="text/javascript">
<!--
abhijeet('abhi', 22 );
//-->
</script>


No syntax-level polymorphism

In some languages, a programmer may write two functions with the same name but a different parameter list and the interpreter/compiler would choose the right one as in the following:

function abhi(a) {

}
function abhi(a,b) {

}

abhi(a) // first function is called
abhi(a,b) // second function is called


That is called function polymorphism. In JavaScript, there’s no such thing.

There can be only one function named abhi, that is called for any given arguments.

So we can say that in JavaScript, a function may be called with any number of arguments, no matter how many of them are listed.

Example:

function abhi(a,b) {
alert(“a=”+a+”, b=”+b)
}

abhi(a) // a=1 b=undefined
abhi(1,2) // a=1 b=2
abhi(1,2,3) // a=1 b=2 , extra argument is not listed


Arguments that are not provided become undefined.