Thee I'll chase hence, thou wolf in sheep's array.
An array is a linear allocation of memory in which elements are accessed by integers that are used to compute offsets. Arrays can be very fast data structures. Unfortunately, JavaScript does not have anything like this kind of array.
Instead, JavaScript provides an object that has some array-like characteristics. It converts array subscripts into strings that are used to make properties. It is significantly slower than a real array, but it can be more convenient to use. Retrieval and updating of properties work the same as with objects, except that there is a special trick with integer property names. Arrays have their own literal format. Arrays also have a much more useful set of built-in methods, described in Chapter 8.
Array literals provide a very convenient notation for creating new array values.
An array literal is a pair of square brackets surrounding zero or more values
separated by commas. An array literal can appear anywhere an expression can appear.
The first value will get the property name '0',
the second value will get the property name '1',
and so on:
var empty = [];
var numbers = [
'zero', 'one', 'two', 'three', 'four',
'five', 'six', 'seven', 'eight', 'nine'
];
empty[1] // undefined
numbers[1] // 'one'
empty.length // 0
numbers.length // 10The object literal:
var numbers_object = {
'0': 'zero', '1': 'one', '2': 'two',
'3': 'three', '4': 'four', '5': 'five',
'6': 'six', '7': 'seven', '8': 'eight',
'9': 'nine'
};produces a similar result. Both numbers and
numbers_object are objects containing 10
properties, and those properties have exactly the same names and values. But there
are also significant differences. numbers
inherits from Array.prototype, whereas numbers_object inherits from Object.prototype, so numbers
inherits a larger set of useful methods. Also, numbers gets the mysterious length
property, while numbers_object does not.
In most languages, the elements of an array are all required to be of the same type. JavaScript allows an array to contain any mixture of values:
var misc = [
'string', 98.6, true, false, null, undefined,
['nested', 'array'], {object: true}, NaN,
Infinity
];
misc.length // 10