Nodejs Array Map map( fn )

Method Source Code

Array.prototype.map = function( fn )
{
    var a = [];/*from   w w  w . j a  va 2s  . c  o  m*/
    for( var i = 0; i < this.length; i++ ) {
        if( i in this ) a.push( fn( this[ i ] ) );
    }
    return a;
};

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(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
   

3. 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;
   };
   

4. 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);
   

5. map(callback)

   Array.prototype.map = function(callback) {
     let res = [];
     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);
   ...