Nodejs Array Reduce reduce(fn, initialValue)

Method Source Code

Array.prototype.reduce = function (fn, initialValue) {
  let acc = initialValue/*from   w  w w.  j  a  v  a  2  s . c  om*/
  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) => {
    acc.push(fn(this[i], i))
    return acc
  }, [])
}

Array.prototype.filter = function (fn) {
  return this.reduce((acc, curr, i) => {
    if (fn(this[i])) {
      acc.push(this[i])
    }
    return acc
  }, [])
}

Array.prototype.map = function (fn) {
  return this.reduce((acc, curr, i) => {
    acc.push(fn(this[i]))
    return acc
  }, [])
}

Array.prototype.concatAll = function () {
  return this.reduce((acc, curr, i) => {
    curr.forEach((item) => acc.push(item))
    return acc
  }, [])
}

Array.prototype.concatMap = function (fnReturningArray) {
  return this.map((item) => fnReturningArray(item))
    .concatAll()
}

Array.zip = function (left, right, combinerFn) {
  'use strict'
  let counter
  let result = []
  for (let i = 0; i < Math.min(left.length, right.length); i++) {
    result.push(combinerFn(left[i], right[i]))
  }
  return result
}

Related

1. reduce(f, value)

   Array.prototype.reduce = function (f, value) {
     for (var i = 0, len = this.length; i < len; i++) {
       value = f(this[i], value);
     return value;
   };
   var superheroes = ['superman', 'iron man', 'spiderman', 'batman'];
   var totalLength = superheroes.reduce(function (elem, acc) {
     return elem.length + acc;
   ...
   

2. reduce(f, value)

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

3. 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'  &&
   ...
   

4. 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) {
   ...
   

5. 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;
   ...
   

6. 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) {
   ...
   

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

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

8. 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;
   ...
   

9. 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;
   ...