JavaScript function declaration, function expression, Function constructor, Anonymous function

December 25, 2012

Function declaration –

function name([param[, param[, ... param]]]) {
example -
function sum(a, b)
    return a + b;

name – The function name

param – The name of the argument to be passed to the function. A function can have up to 255 arguments.

statements – The body of the function

Function expression and Anonymous function –

function [name]([param] [, param] [..., param]) {
example -
var sum = function(a, b) { return a + b; }

The name can be omitted in which case it becomes anonymous function.
Anonymous functions can help make code more concise when declaring a function that will only be used in one place.

Function constructor –

Function objects can be created with new operator

new Function (arg1, arg2, ... argN, functionBody)

example - 
var sum = new Function('a','b', 'return a + b;');

arg1, arg2, … argN – zero or more names to be used by the function as argument names

functionBody – A string containing JavaScript statements forming the function body.