JavaScript 中 map、foreach、reduce 间的区别

people.forEach(function (dude) {
  dude.pickUpSoap();});

var wallets = people.map(function (dude) {
  return dude.wallet;});

var totalMoney = wallets.reduce(function (countedMoney, wallet) {
  return countedMoney + wallet.money;}, 0);

var fatWallets = wallets.filter(function (wallet) {
  return wallet.money > 100;});

Array.prototype.map = function (fn) {
    var resultArray = [];
    for (var i = 0,len = this.length; i < len ; i++) {
         resultArray[i] = fn.apply(this,[this[i],i,this]);
    }
    return resultArray;}

Array.prototype.forEach = function (fn) {
    for (var i = 0,len = this.length; i < len ; i++) {
         fn.apply(this,[this[i],i,this]);
    }}

Array.prototype.reduce= function (fn) {
    var formerResult = this[0];
    for (var i = 1,len = this.length; i < len ; i++) {
         formerResult = fn.apply(this,[formerResult,this[i],i,this]);
    }
    return formerResult;}