Nodejs Array Reduce reduce(aggregate, initial)

Method Source Code

Array.prototype.reduce = function(aggregate, initial) {
  const len = this.length;
  let startIndex = 0;// ww w  . j  av  a  2 s.c om
  if(typeof initial === 'undefined') {
    initial = this[0];
    startIndex = 1;
  }
  for(let i = startIndex; i < len; i += 1) {
    initial = aggregate(initial, this[i], i, this);
  }
  return initial;
};

Related

1. reduce()

   Array.prototype.reduce = function() {
     return this.length > 1 ? this : this[0];
   };
   

2. reduce()

   var testArray1 = [1, 3, 5, 4, 2],
         sumArray = [];
   Array.prototype.reduce = function() {
     var sum = 0;
       for (i=0;i<this.length; ++i) {
       sum += this[i];
         return sumArray.push(sum);
   };
   ...
   

3. reduce(callback, initial)

   Array.prototype.reduce = function(callback, initial){
     initial = initial || 0;
     for (var i=0; i< this.length; i++) {
       initial = callback(initial, this[i], i, this);
     return  initial;
   wat = [1,2, 3, 4]
   console.log(wat);
   ...
   

4. reduce(callback, initialValue)

   Array.prototype.reduce = function(callback, initialValue) {
     var last, returned;
     this.forEach(function(item, index, array) {
       if (index == 0 && initialValue) {
         returned = initialValue;
       } else if (index == 1 && !initialValue) {
         returned = item;
       } else {
         last = returned, returned = null;
   ...
   

5. reduce(callback, memo)

   Array.prototype.reduce = function (callback, memo) {
       var obj = this;
       var value, accumulated_value = 0;
       for (var i = 0; i < obj.length; i++) {
           value = obj[i];
           accumulated_value = callback.call(null, accumulated_value, value);
       return accumulated_value;
   };
   ...
   

6. reduce(cb, res)

   Array.prototype.reduce = function(cb, res){
       var arr = Object(this);
       for(var i=0;i<arr.length;i++){
           res = cb.call(res, arr[i], i);
       return res;