JavaScript Cookbook

Chapter 5. Working with Arrays and Loops

5.0. Introduction

An array is an ordered collection of elements. In JavaScript, an array can be created using formal object notation, or it can be initialized using literal notation, as demonstrated in the following code:

var arrObject = new Array("val1", "val2"); // array as object
var arrLiteral = ["val1", "val2"]; // array literal

To the developer, there is no difference: you can invoke an Array method on both a literal and an object. However, to the JavaScript engine, an array literal has to be reinterpreted each time it’s accessed, especially when used in a function call. On the positive side, though, array literals can replace the need for temporary variables, especially when sending values to a function.

A new Array object is created using the new operator, as follows:

var arrObject = new Array();

You can also create a new array that has some values:

var arrObject = new Array("val1","val2");

You can create an array literal by using square brackets to hold the array values. For instance, you can define an array literal and assign it to a variable:

var arrLiteral = ["val1","val2","val3"];

You can also create, and use, a literal array in a function or method call:

someFunction("param1", ["val1","val2"]);

Note, though, that when you pass a variable containing an array literal to a function, it is passed by reference—the same as passing a variable holding an Array object. Changes to the variable in the function are reflected outside of the function: ...