Learning JavaScript

JavaScript Arrays

There’s an interesting little fact about JavaScript: if there’s an object, there’s also a literal. As shown in the last few chapters, there’s a String object and string literals; the same is true of Boolean and boolean, and Number and numbers. We also used this with regular expressions, and rarely referenced the RegExp object directly in the examples. This same object/literal relationship holds true with arrays.

Constructing Arrays

A JavaScript array is an object, just like String or Math. As such, it’s created with a constructor:

var newArray = new Array('one','two');

An array is also a literal value, which doesn’t require the explicit use of the Array object:

var newArray = ['one','two'];

In this latter case, the JS engine converts the literal to an object of type Array, assigning the result to the variable. Once created, array elements can be accessed by their index value—the number representing their location in the array:

alert(newArray[0]); // outputs one

Array indexes start at 0 and go up to the number of elements, minus 1. So an array of five elements would have indexes from 0 to 4.

Arrays don’t have to be one-dimensional. It’s not uncommon to have an array in which each element has multiple dimensions, and the way to manage this in JS is to create an array where each element is an array itself. In the following code snippet, an array of three-dimensional values is created:

var threedPoints = new Array(  ); threedPoints[0] = new Array(1.2,3.33,2.0); threedPoints[1] ...