var numbers = [1, 4, 9]; var roots = numbers.map(Math.sqrt); // roots的值为[1, 2, 3], numbers的值仍为[1, 4, 9]
sqrt:用来计算一个非负实数的平方根
var numbers = [1, 4, 9]; var doubles = numbers.map(function(num) { return num * 2; }); // doubles数组的值为: [2, 8, 18] // numbers数组未被修改: [1, 4, 9]
var map = Array.prototype.mapvar a = map.call("Hello World", function(x) { return x.charCodeAt(0); }) // a的值为[72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100]