Javascript Array map(projection)

'use strict';/*ww w  . j  a v a 2  s.  com*/

Array.prototype.map = function (projection) {
    var results = [];
    this.forEach(function (element) {
        results.push(projection(element))
    });
    return results;
};

// 2 The Array map method

function getStockSymbols(stocks) {
  return stocks.map(function(stock) {
    return stock.symbol;
  });//from   w  w w .j a va2 s .  co  m
}

Array.prototype.map = function(projection) {
  var results = [];

  this.forEach(function(item) {
    results.push(projection(item));
  });

  return results;
}

var symbols = getStockSymbols([
  { symbol: "XFX", price: 240.22, volume: 23432 },
  { symbol: "TNJ", price: 332.19, volume: 234 },
  { symbol: "JXJ", price: 120.22, volume: 5323 }
]);

console.log(symbols); // [ 'XFX', 'TNJ', 'JXJ' ]