Nodejs Array Map map(callback)

Method Source Code

Array.prototype.map = function(callback) {
  let res = [];/*from w w w.  ja v  a 2 s  . c o  m*/
  this.forEach(el => res.push(callback(el)));
  return res;
};

let a = [1,2,3];
let b = a.map(el => el * el);
console.log(a);
console.log(b);


function foldingCipher(str) {
  let alph = 'abcdefghijklmnopqrstuvwxyz'.split('');
  let res = '';

  for (let i = 0; i<str.length; i++) {
    let idx = 25 - alph.indexOf(str[i]);
    res += alph[idx];
  }
  return res;

}

console.log(foldingCipher('abcxyz'));
console.log(foldingCipher('xyzabc'));

Related

1. map( func /*, obj */)

   Array.prototype.map = function(  func ) {
     var len = this.length;
     if (typeof func != 'function') {
       throw new Error("argument must be function");
     };
     var res = [];
     var obj = arguments[1];
     console.log("obj" + obj)
     for (var i = 0; i < len; i++) {
   ...
   

2. map( fn )

   Array.prototype.map = function( fn )
       var a = [];
       for( var i = 0; i < this.length; i++ ) {
           if( i in this ) a.push( fn( this[ i ] ) );
       return a;
   };
   

3. map(a)

   Array.prototype.map = function(a) {
     const array = new Array(this.length)
     for (let i = 0; i < this.length; i++) array[i] = a(this[i], i, this)
     return array
   

4. map(callback)

   Array.prototype.map = function(callback) {
     var result = [];
     for(var i = 0; i < this.length; i += 1) {
       result.push(callback.call(this[i]));
     return result;
   };
   

5. map(callback)

   Array.prototype.map = function (callback) {
       var obj = this;
       var value, mapped_value;
       var A = new Array(obj.length);
       for (var i = 0; i < obj.length; i++) {
           value = obj[i];
           mapped_value = callback.call(null, value);
           A[i] = mapped_value;
       return A;
   };
   var arr = [1, 2, 3];
   var new_arr = arr.map(function (value) {
       return value * value;
   });
   console.log(new_arr);
   

6. map(callback)

   Array.prototype.map = function(callback){
     var a = 0,
       len = this.length,
       result = [];
     while(a < len){
       result.push(callback(this[a], a++, this));
     return result;
   };
   ...
   

7. map(callback)

   Array.prototype.map = function(callback){
       const newArr = []
       for(let i = 0; i < this.length; i += 1){
           let newValue = callback(this[i])
           newArr.push(newValue)
       return newArr
   var someArray = [1,2,3,4]
   ...
   

8. map(callback)

   Array.prototype.map = function(callback) {
     for(var i = 0, l = this.length; i < l; i++) {
       this[i] = callback(i, this[i]);
     return this;
   

9. map(callback)

   Array.prototype.map = function (callback) {
     var mapped = [];
     function mutation(el) {
       mapped.push(callback(el));
     this.each(mutation);
     return mapped;
   };