Nodejs Array Reduce reduce(callback, initialValue)

Method Source Code

// https://developer.mozilla.org/en/New_in_JavaScript_1.8

// https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Global_Objects/Array/Reduce
// [1, 2, 3].reduce(function(sum, item) { return sum + item }, 0)
Array.prototype.reduce = function(callback, initialValue) {
  var last, returned;
  this.forEach(function(item, index, array) {
    if (index == 0 && initialValue) {
      returned = initialValue;//from ww w  . j av a 2s  .  c  om
    } else if (index == 1 && !initialValue) {
      returned = item;
    } else {
      last = returned, returned = null;
      returned = callback(last, item, index, array);
    };
  });
  return returned;
};

// functional-style
// ladit pres file:///Users/botanicus/Desktop/index.html
Array.prototype.reduce = function(callback, initialValue) {
  // var tail = this, head = initialValue || tail.shift(), initialValue = null;
  var head = initialValue || this.shift();
  var tail = this;
  var initialValue = null;
  if(tail) {
    tail.reduce(callback, head);
  } else {
    return head;
  }
};
[1, 2, 3].reduce(function(sum, item) { return sum + item })

Array.prototype.reduceRight

String.prototype.trim
String.prototype.trimLeft
String.prototype.trimRight

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(aggregate, initial)

   Array.prototype.reduce = function(aggregate, initial) {
     const len = this.length;
     let startIndex = 0;
     if(typeof initial === 'undefined') {
       initial = this[0];
       startIndex = 1;
     for(let i = startIndex; i < len; i += 1) {
       initial = aggregate(initial, this[i], i, this);
   ...
   

4. 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);
   ...
   

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;
   

7. reduce(combiner, initialValue)

   Array.prototype.reduce = function (combiner, initialValue) {
     var counter,
       accumulatedValue;
     if (this.length === 0) {
       return this;
     else {
       if (arguments.length === 1) {
         counter = 1;
   ...
   

8. reduce(combiner, initialValue)

   Array.prototype.reduce = function(combiner, initialValue) {
     var counter,
       accValue;
     if (this.length === 0) {
       return this;
     else {
       if (arguments.length === 1) {
         counter = 1;
   ...