7 Best Use Case of JavaScript Array Method map(), filter() and reduce()

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7 Best Use Case of JavaScript Array Method map(), filter() and reduce()
Coy  Roberts

Coy Roberts


Definitive Guide to Understand Javascript Array reduce()

Javascript array reduce() is an inbuilt method that is used to apply a function to each element in the array to reduce the array to a single value. The reduce() function executes the provided function for each value of an array from left-to-right. The return value of a function is stored in an accumulator.

Understanding Javascript array reduce()

JavaScript array reduce() is one of the pioneer function of functional programming. The reduce() method accepts two parameters, the total and the current value. If you want to add all the values of an array, then use the array reduce() function.

It is similar to both  Javascript map() and  Javascript filter() but, it differs in the callback arguments.

The callback now receives an accumulator (it accumulates all the return values. Its value is the accumulation of a previously returned accumulations), a current value, a current index, and finally, the whole array.

#javascript #javascript map #javascript filter #javascript array reduce

Coy  Roberts

Coy Roberts


Array Foreach, Map, Filter, Reduce, Concat Methods in Javascript

In this tutorial, we will see Javascript Array Foreach, Map, Filter, Reduce, Concat Methods. I dedicate this article only for these methods because, in Pure Functional Programming, this kind of method is required to perform some operations on an Array.

If you do not know What Pure Functions is, then check out my Pure Functions in Javascript article on this website.


All the programming languages have this kind of Data Structure to hold and manipulate the data and Javascript is not different.

We all know Arrayscollection of variables, and we all have used to perform some operations like Creating an array, Removing an Item from an Array, Sorting the data of an Array and other manipulations.

In Functional Programming, we are using functions like foreach, map, filter, reduce, concatAll and other Higher Order Functions. So today I am describing these functions in deep and show you how you can use it in various scenarios.

#javascript #programming #foreach #map #filter #reduce

Terry  Tremblay

Terry Tremblay


Fill and Filter in Array in JavaScript

By the word Array methods, I mean the inbuilt array functions, which might be helpful for us in so many ways. So why not just explore and make use of them, to boost our productivity.

Let’s see them together one by one with some amazing examples.


The _fill()_ method changes all elements in an array to a static value, from a start index (default _0_) to an end index (default _array.length_). It returns the modified array.

In simple words, it’s gonna fill the elements of the array with whatever sets of params, you pass in it. Mostly we pass three params, each param stands with some meaning. The first param value: what value you want to fill, second value: start range of index(inclusive), and third value: end range of index(exclusive). Imagine you are going to apply this method on some date, so that how its gonna look like eg: array.fill(‘Some date’, start date, end date).

NOTE: Start range is inclusive and end range is exclusive.

Let’s understand this in the below example-

//declare array
var testArray = [2,4,6,8,10,12,14];


When you run this code, you gonna see all the elements of testArray will be replaced by 'A' like [“A”,"A","A","A","A","A","A"].

#javascript-tips #array-methods #javascript-development #javascript #arrays

Giles  Goodwin

Giles Goodwin


Maps in JavaScript

What topics we are going to cover?

  1. What are Maps?
  2. What are the methods used in it and how we can insert or retrieve values to it?
  3. How Maps works, behave with loops and what is happening behind the scenes?

What are Maps?

By the word Map, here I mean another new method which is being used these days in modern JavaScript. Here we are going to see the classic dataType of Map. Mostly Map is getting used in looping concepts that’s a great thing, but if you go directly for all those then you won’t be able to understand the classic dataType of Map.

So let’s fire up our code editor and understand the concepts of Map with some amazing examples.

var myMap = new Map();

This is almost kind of constructional approach, where we create an object from prototype and stuff like that.

What are the methods used in Maps?

Now Map has a lot of properties and I think you should take a look at it, at once. So whenever you gonna type myMap. then you can see a list of methods will be appearing on your screen like- get, set, forEach, values, and bunch of things. So one of the common methods which are being used widely is set and get method and by this time I guess from its name itself you might have guessed it like these are some default setters and getters means it can add values to them and retrieve values from them.

How to insert values in Maps?

Let’s go ahead and try with set() method and have some of the fun together:

Note: They work almost like objects but remember this, Maps are not like objects, they are completely different.

var myMap = new Map();
myMap.set(1, "Ricky"); //myMap.set(any key, any value)
myMap.set(2, "Monty"); //myMap.set(any key, any value)
myMap.set(3, "Henna"); //myMap.set(any key, any value)
myMap.set(4, "Monta"); //myMap.set(any key, any value)

Now if you try to run this code in your editor, then you gonna see an output like this on your screen.

Map(4) { 1 => 'Ricky', 2 => 'Monty', 3 => 'Henna', 4 => 'Monta' }

Notice here, how Maps by default itself is telling you that how many properties you are storing in it and one more thing you can see here they have used => these arrow between its key, value pair to differentiate, and make you understand that they are not your regular objects.

#javascript-development #maps #array-methods #arrays #javascript

map(), filter() and reduce() in JavaScript.

**_map, filter and reduce _**are essentially just some of the most well-known, easy to use, higher-order functions that run provided callback on each element of an array.

In this article, we will explore how using map(), filter(), and reduce() can help make our code:

**1.**Easy to comprehend.

2. Less prone to side effects as these function don’t modify the actual array, and instead create a new one.

**3. **Avoid explicit loops.

Let’s explore and familiarize ourselves with these functions.

#functional-programming #filters #maps #javascript #reduce