Functional Programming in JavaScript - 5

gistfile1.js

var forEach = function (list, action) {
  for (var i = 0; i < list.length; i++) {
    action(list[i]);
  }
};

var map = function (mappingFunction, list) {
  var result = [];
  forEach(list, function (item) {
    result.push(mappingFunction(item));
  });
  return result;
};

var doubleIt = function (item) {
  if (typeof item === "number") {
    return item * 2;
  }
};

console.log(map(doubleIt, [1, 2, 3, 4, "WTF"]));