Many programming languages support arrays with named indexes. Arrays with named indexes are called associative arrays (or hashes). JavaScript does not support arrays with named indexes. In JavaScript, arrays always use numbered indexes.
var person = [];
person[0] = "John";
person[1] = "Doe";
person[2] = 46;
var x = person.length;
// person.length will return 3
var y = person[0];
// person[0] will return "John"