Nodejs Array Reduce reduce(fun /*, initial*/)

Method Source Code

/*=pod// w w w .  j  av  a  2s.  co m

=head2 reduce( Function fun, Any initialValue? ) Returns Any

Apply fun() against two values of the array (from left-to-right) as to reduce it to a single value and return that value.

=cut*/

Array.prototype.reduce = function(fun /*, initial*/)
{
   var len = this.length;
   if (typeof fun != "function") {
      throw new TypeError();
   }

   // no value to return if no initial value and an empty array
   if (len == 0 && arguments.length == 1) {
      throw new TypeError();
   }

   var i = 0;
   if (arguments.length >= 2) {
      var rv = arguments[1];
   } else {
      do {
         if (i in this) {
            rv = this[i++];
            break;
         }

         // if array contains no values, no initial value to return
         if (++i >= len) {
            throw new TypeError();
         }
      } while (true);
   }

   for (; i < len; i++) {
      if (i in this) {
         rv = fun.call(null, rv, this[i], i, this);
      }
   }

   return rv;
};

Related

1. reduce(f, value)

   var is_array_01 = function (value) {
     return value &&
       typeof value === 'object' &&
       value.constructor === Array;
   };
   var is_array = function (value) {
     return value &&
       typeof value === 'object'  &&
       typeof value.length === 'number'  &&
   ...
   

2. reduce(f, value)

   Array.prototype.reduce = function(f, value) {
       var i;
       for (i = 0; i < this.length; i += 1) {
           value = f(this[i], value);
       return value;
   };
   var data = [ 4, 8, 15, 16, 23, 42 ];
   var add = function(a, b) {
   ...
   

3. reduce(fn, initial)

   Array.prototype.reduce = function(fn, initial)
       var r, i;
       initial ? r = initial : r = this[0];
       for (i=1;i<this.length;i++)
           r = fn(r, this[i]);
       return r;
   ...
   

4. reduce(fn, initialValue)

   Array.prototype.reduce = function (fn, initialValue) {
     let acc = initialValue
     for (var i = 0; i < this.length; i++) {
       acc = fn(acc, this[i], i)
     return acc
   Array.prototype.forEach = function (fn) {
     this.reduce((acc, curr, i) => {
   ...
   

5. reduce(fun /* , initial */)

   if (!Array.prototype.reduce) {
     Array.prototype.reduce = function(fun ) {
       var len = this.length >>> 0;
       if (typeof fun != "function")
         throw new TypeError();
       if (len == 0 && arguments.length == 1)
         throw new TypeError();
       var i = 0;
       if (arguments.length >= 2) {
   ...
   

6. reduce(fun /*, initial*/)

   Array.prototype.reduce = Array.prototype.reduce || function(fun ) {
       var len = this.length >>> 0;
       if (typeof fun != "function") {
           throw new TypeError();
       if (len == 0 && arguments.length == 1) {
           throw new TypeError();
       var i = 0;
   ...
   

7. reduce(pasteback, initial)

   'use strict';
   Array.prototype.reduce = function(pasteback, initial){
     for(var i = 0
         , c =  this.length
         , value = arguments.length>1 ? initial : this[i++]
     ; i<c; i++){
       value = pasteback(value, this[i], i, this);
     return value;
   ...
   

8. reduce(process, initial)

   Array.prototype.reduce = function(process, initial) {
     var value = initial;
     for (var i = 0; i < this.length; i++) {
       if( ( i === 0 ) && ( value === undefined || value === null ))
           value = this[0];
           continue;
       value = process( value, this[i] );
   ...
   

9. reduce(process, initial)

   Array.prototype.reduce = function(process, initial) {
     if (initial === undefined) {
       var slice = this.slice(1);
       initial = this[0];
     var array = slice || this;
     array.forEach(function(value) {
       initial = process(initial, value);
     });
   ...