JavaScript Tutorials

Object and Array initializers

Object and array initializers are expressions whose value is a newly created object or array. These initializer expressions are sometimes called “object literals” and “array literals.” Unlike true literals, however, they are not primary expressions, because they include a number of subexpressions that specify property and element values. Array initializers have a slightly simpler syntax, and we’ll begin with those. An array initializer is a comma-separated list of expressions contained within square brackets. The value of an array initializer is a newly created array. The elements of this new array are initialized to the values of the comma-separated expressions:

[] // An empty array: no expressions inside brackets means no elements
[1+2,3+4] // A 2-element array. First element is 3, second is 7

Object initializer expressions are like array initializer expressions, but the square brackets are replaced by curly brackets, and each subexpression is prefixed with a property name and a colon:

var p = { x:2.3, y:-1.2 }; // An object with 2 properties

var q = {}; // An empty object with no properties
q.x = 2.3; q.y = -1.2; // Now q has the same properties as p