Nodejs Array Map map(callback)

Method Source Code

Array.prototype.map = function(callback){
    const newArr = []//from   w  w w .jav a  2s .c  o m
    // console.log(this)
    // callback();
    for(let i = 0; i < this.length; i += 1){
        let newValue = callback(this[i])
        // let newValue = callback(this[i],i,this)
        // reference the index and array
        newArr.push(newValue)
    }
    return newArr
}

var someArray = [1,2,3,4]
const returnArray = someArray.map(function(value){
    // const returnArray = someArray.map(function(value, index, array){
    return value
});
console.log(returnArray)

Related

1. 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
   

2. 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;
   };
   

3. 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);
   

4. 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);
   ...
   

5. 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;
   };
   ...
   

6. 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;
   

7. map(callback)

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

8. map(callback)

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

9. map(callback)

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