Nodejs Array Reduce reduce(f, value)

Method Source Code

// Description: Extending all arrays by extending Array Prototype in JavaScript

// Note/*from w w w . j ava2  s  .  c o  m*/
// 1. JavaScript provides a set of methods for acting on arrays. These methods are functions stored in Array.prototype.
// 2. Array.prototype can be augmented to add custom array functionality.
// 3. Adding a function to Array.prototype, makes it available to every array.

// 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 sample array of numbers
var data = [ 4, 8, 15, 16, 23, 42 ];

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

// A function to multiple two numbers.
var mult = function(a, b) {
    return a * b;
};

// Invoke the data's reduce method, passing in the add function.
var sum = data.reduce(add, 0); // The sum is 108

// Invoke the reduce method again, this time passing in the multiply function.
var product = data.reduce(mult, 1); // The product is 7418880

console.log("sum: " + sum);
console.log("product: " + product);

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;
};
...

reduce(f, value)

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

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;
...

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) {
...

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'  &&
...

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;
...

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) => {
...

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) {
...

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;
};

Nodejs Array Reduce reduce(f, value)

Method Source Code

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