JavaScript Functions

If you read my previous post about objects (Nested Objects in JavaScript) in JavaScript Objects are the kings. You can find only two things in JavaScript, objects and primitives. Do you know that Functions are also objects in JavaScript, functions inherited from objects, In JavaScript we can find 2 types of JavaScript function definitions.

·         Function declaration

·         Function expression

They're actually really similar. How you call them is exactly the same, but the difference lies in how the browser loads them into the execution context. Function declarations loads before any code is executed. While function expressions loads only when the interpreter reaches that line of code. So if you try to call a function expression before it's loaded, you'll get an error but if you call a function declaration, it'll always work. Because no code can be called until all declarations are loaded, before drilling down into the depth of this problem lets have simple understanding of each.

Function Declaration

Function expression

Now it’s the right time to discuss about hoisting .Hoisting is JavaScript's default behavior of moving declarations to the top of the current scope. Hoisting applies to

• Variable declarations 
• Function declarations. (Because of this, JavaScript functions can be called before they are declared).

Functions defined using an expression are not hoisted. Read more on hoisting (http://www.w3schools.com/js/js_hoisting.asp )

The Function () Constructor

It’s really discouraging to write your function using default Function constructor, because of its messy appearance.

Self-Invoking Functions

This self-invoking expressions are invoked automatically. When functional expression followed by () it’s automatically invoked and this mechanism is not working with function declaration.

Also functions can use within expressions.

As I state earlier functions are objects. Then as usual functions should have methods and properties. Then you may think of what are the methods and properties of function object.

Let’s see few of the important objects things that you can do with a function in JavaScript

Function is an instance of object type

When we run above script it gives “true”

Function has its own properties

When we discuss about JavaScript functions we need to have some idea about closure and recursion.

Recursion

If you dealing with any programming language probably you may know the meaning of recursion .when a function calling itself we called it as recursion.

Always when I hear the word recursion factorial numbers are the first thing comes into my mind. Let’s look at a simple example which use recursion to display the value of a factorial number.

Closure

A closure is an inner function that has access to the outer (enclosing) function’s variables—scope chain. The closure has three scope chains: it has access to its own scope (variables defined between its curly brackets), it has access to the outer function’s variables, and it has access to the global variables. As this topic should discuss in an informative way hope to have another post on JavaScript Closure.

Hope above information help you in understanding functions in JavaScript. Until meet next time HAPPY CODING J