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 7Object 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