Nodejs Array Map map2(projection)

Method Source Code

// https://egghead.io/lessons/javascript-the-array-map-method

const stocks= [//from   w w w . j  a  va2 s  . co  m
  {symbol: 'XFX', price: 240.22, volume: 23432},
  {symbol: 'TNZ', price: 332.19, volume: 234},
  {symbol: 'JXJ', price: 120.22, volume: 5323},
]

Array.prototype.map2= function(projection) {
  let results= []
  this.forEach(item => results.push(projection(item)))
  return results
}

const getStockSymbols= stocks => stocks.map2(stock => stock.symbol)

console.log('\nVIDEO 02')
console.log(JSON.stringify(getStockSymbols(stocks)))

Related

1. map(projectionFunction)

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

2. map(projectionFunction)

   Array.prototype.map = function(projectionFunction) {
     var results = [];
     this.forEach(function(itemInArray) {
     });
     return results;
   };
   JSON.stringify(
     [1,2,3].map(function(x) {
       return x + 1;
   ...
   

3. map(testFunction)

   Array.prototype.map = function(testFunction){
     var result = [];
     this.forEach(function(item){
       result.push(testFunction(item));
     })
     return result;
   

4. map(transform)

   Array.prototype.map = function (transform) {
     let mappedArray = [];
     const len = this.length;
     for (let i = 0; i < len; i += 1) {
       mappedArray.push(transform(this[i], i, this));
     return mappedArray;
   };
   

5. map(transformer)

   Array.prototype.map = function(transformer) {
     var result = []
     for ( var i = 0; i < this.length; i++) {
       result.push(transformer(this[i]));
     return result;
   

6. mapByTwo(fun /*, thisp*/)

   Array.prototype.mapByTwo = function(fun ) {
     if (typeof fun != "function")
       throw new TypeError();
     var len = this.length >>> 0;
     var thisp = arguments[1];
     var k = 0;
     var A = new Array(Math.ceil(len/2));
     if (len/2 < A.length) {
       this.push(null);
   ...
   

7. mapMe(func)

   Array.prototype.mapMe = function (func) {
     var arr = this, result = [];
     for (var i = 0; i < arr.length; i++) {
       result.push(func(arr[i]));
     return result;
   };
   

8. mapValues(value)

   Array.prototype.mapValues = function(value) { 
       return this.map(function(e) { 
           return e[value] 
       })
   

9. mapp(callback)

   Array.prototype.mapp = function(callback) {
     var newArray = [];
     for(var i = 0; i < this.length; i++){
       newArray.push(callback(this[i]));
     return newArray;
   var x = [1,2,3];
   x.mapp(function(ele) {
   ...