Nodejs Array Map map( func /*, obj */)

Method Source Code

Array.prototype.map = function(  func /*, obj */) {
  var len = this.length;

  if (typeof func != 'function') {
    throw new Error("argument must be function");
  };//from   ww  w  . j  a  v a 2 s .c  o m

  var res = [];
  var obj = arguments[1];
  console.log("obj" + obj)

  for (var i = 0; i < len; i++) {
    res[i]  = func.call(obj, this[i], i, this);
  };

  return res;
}


function double(x) {
  return x*2;
}

console.log([1,2,3,4,5].map(double));

Related

1. 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;
   };
   

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);