Nodejs Array Reduce reduce(f, value)

Method Source Code

// Description: Extending an Array in JavaScript

// Note// w  w w.j a v a 2s . c  o  m
// 1. Since an array is really an object, methods can be added directly to an individual array instead of the
//    array.Prototype.

var data = [ 4, 8, 15, 16, 23, 42 ];

// Adding a method to Array.prototype to extend all arrays.
Array.prototype.reduce = function(f, value) {
    var i;
    for (i = 0; i < this.length; i += 1) {
        value = f(this[i], value);
    }

    return value;
};

// A function to add two numbers.
var add = function(a, b) {
    return a + b;
};

// Add a total function to the data array. This function extends ONLY the data array.
data.total = function() {
    return this.reduce(add, 0);
};

// Invoke the total function.
total = data.total(); // total is 108
console.log("total: " + total);

Related

1. 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);
   ...
   

2. 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;
   };
   ...
   

3. reduce(f, initial)

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

4. reduce(f, value)

   Array.prototype.reduce = function (f, value) { 
       for (var i = 0; i < this.length; i++) { 
           value = f(this[i], value)
       return value
   

5. 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;
   ...
   

6. 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'  &&
   ...
   

7. 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) {
   ...
   

8. 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;
   ...
   

9. 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) => {
   ...