gistfile1.js

// using node.js

var sys = require("sys");

var balls = [1, 2, 3, 4];

sys.puts("\n// for...in loop: before prototype\n");
for (var i in balls) {
  sys.puts(balls[i]);
}

// => 1, 2, 3, 4

Array.prototype.sam = function () {};

Array.prototype.iam = function () {};

sys.puts("\n// for...in loop: after prototype\n");
for (var i in balls) {
  sys.puts(balls[i]);
}

// => 1, 2, 3, 4, function () {}, function () {}

sys.puts("\n// for loop\n");
for (var i = 0, ii = balls.length; i < ii; i++) {
  sys.puts(balls[i]);
}

// => 1, 2, 3, 4