JavaScript Pocket Reference, 3rd Edition

Chapter 6. Arrays

An array is an ordered collection of values. Each value is called an element, and each element has a numeric position in the array, known as its index. JavaScript arrays are untyped: an array element may be of any type, and different elements of the same array may be of different types. Array elements may even be objects or other arrays, which allows you to create complex data structures, such as arrays of objects and arrays of arrays. JavaScript arrays are zero-based and use 32-bit indexes: the index of the first element is 0, and the highest possible index is 4294967294 (2³²−2), for a maximum array size of 4,294,967,295 elements. JavaScript arrays are dynamic: they grow or shrink as needed and there is no need to declare a fixed size for the array when you create it or to reallocate it when the size changes. Every JavaScript array has a length property that specifies the number of elements in the array.

JavaScript arrays are a specialized form of JavaScript object, and array indexes are really little more than property names that happen to be integers. Implementations typically optimize arrays so that access to numerically indexed array elements is faster than access to regular object properties.

Arrays inherit properties from Array.prototype, which defines a rich set of array manipulation methods. Most of these methods are generic, which means that they work correctly not only for true arrays, but for any “array-like object.” In ECMAScript 5, strings behave like ...