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Variable declaration

Module by: Hannes Hirzel. E-mail the author

Summary: This module explains how variables are declared in JavaScript (ECMAScript).

Introduction

In JavaScript variables are declared with the var keyword, e.g. var theName;. You may initialize the variable at the same time, thus var theName = "John";.

If you omit the var keyword and just do introduce the variables by using them they are declared as global variables. This may happen anywhere in the code, including within functions. So use the var all the time within functions to declare local variables.

In EMCAScript5 you may use the "use strict"; directive either on the global level or within a function. It it is used within a function it only applies to that function. It means that all the variables must be declared with the var keyword.

Examples


var myObj1;  // myObj1 is initialized to undefined
var myObj2 = new Object(); // using the constructor function to initialize with an empty object
var myObj3 = {};     // literal notation for initialization with an empty object



var myString = "hello"; 
var myArray = new Array();

Reference

ECMAScript language specification; chapter 12.2 -- variable statement

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