Nodejs Array Reduce reduce(combiner, initialValue)

Method Source Code

// [1,2,3].reduce(function(accumulatedValue, currentValue) { return accumulatedValue + currentValue; }); === [6];
// [1,2,3].reduce(function(accumulatedValue, currentValue) { return accumulatedValue + currentValue; }, 10); === [16];

Array.prototype.reduce = function(combiner, initialValue) {
   var counter,//from  w  ww  .j a v  a 2s.co m
      accumulatedValue;

   // If the array is empty, do nothing
   if (this.length === 0) {
      return this;
   }
   else {
      // If the user didn't pass an initial value, use the first item.
      if (arguments.length === 1) {
         counter = 1;
         accumulatedValue = this[0];
      }
      else if (arguments.length >= 2) {
         counter = 0;
         accumulatedValue = initialValue;
      }
      else {
         throw "Invalid arguments.";
      }

      // Loop through the array, feeding the current value and the result of
      // the previous computation back into the combiner function until
      // we've exhausted the entire array and are left with only one value.
      while(counter < this.length) {
         accumulatedValue = combiner(accumulatedValue, this[counter])
         counter++;
      }

      return [accumulatedValue];
   }
};

Related

1. 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;
   ...
   

2. 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;
   };
   ...
   

3. 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;
   

4. 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;
   ...
   

5. 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;
   ...
   

6. reduce(combiner, initialValue)

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

7. reduce(combiner, initialValue)

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

8. reduce(f, firstValue)

   Array.prototype.reduce = function(f, firstValue){
      var value = firstValue;
      for (var i =0; i<this.length; i++){
         value = f(this[i], value);
      return value;
   };
   [1,2,3].reduce(function(currentValue ,value){return value+=currentValue;}, 0);
   [1,2,3].reduce(function(currentValue ,value){return value*=currentValue;}, 0);
   ...
   

9. reduce(f, inital)

   var arr = [0,1,2,3,4];
   var sum = function(x, y) { return x + y; };
   Array.prototype.reduce = function(f, inital) {
       var acc = initial;
       for (var i = 0; i < this.length; i++) {
           acc = f(acc, this[i]);
       return acc;
   };
   ...