var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
arr.map(pow); // [1, 4, 9, 16, 25, 36, 49, 64, 81]

写成

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
var newArr = arr.map(pow); // [1, 4, 9, 16, 25, 36, 49, 64, 81]

更好理解