JavaScript Map, Reduce, and Filter: What, Why and How to use it

JavaScript Map, Reduce, and Filter - Explained with Examples

Map, reduce, and filter are all array methods in JavaScript. Each one will iterate over an array and perform a transformation or computation. Each will return a new array based on the result of the function. In this article, you will learn why and how to use each one.

Here is a fun summary by Steven Luscher:

var new_array = arr.map(function callback(element, index, array) {
    // Return value for new_array
}[, thisArg])

const numbers = [1, 2, 3, 4];
const doubled = numbers.map(item => item * 2);
console.log(doubled); // [2, 4, 6, 8]

var new_array = arr.filter(function callback(element, index, array) {
    // Return true or false
}[, thisArg])

const numbers = [1, 2, 3, 4];
const evens = numbers.filter(item => item % 2 === 0);
console.log(evens); // [2, 4]

const students = [
  { name: 'Quincy', grade: 96 },
  { name: 'Jason', grade: 84 },
  { name: 'Alexis', grade: 100 },
  { name: 'Sam', grade: 65 },
  { name: 'Katie', grade: 90 }
];

const studentGrades = students.filter(student => student.grade >= 90);
return studentGrades; // [ { name: 'Quincy', grade: 96 }, { name: 'Alexis', grade: 100 }, { name: 'Katie', grade: 90 } ]

arr.reduce(callback[, initialValue])

const numbers = [1, 2, 3, 4];
const sum = numbers.reduce(function (result, item) {
  return result + item;
}, 0);
console.log(sum); // 10

var pets = ['dog', 'chicken', 'cat', 'dog', 'chicken', 'chicken', 'rabbit'];

var petCounts = pets.reduce(function(obj, pet){
    if (!obj[pet]) {
        obj[pet] = 1;
    } else {
        obj[pet]++;
    }
    return obj;
}, {});

console.log(petCounts); 

/*
Output:
 { 
    dog: 2, 
    chicken: 3, 
    cat: 1, 
    rabbit: 1 
 }
 */

#JavaScript #WebDev #javascript

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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

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

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.

Arrays

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

How to create a calculator using javascript - Pure JS tutorials |Web Tutorials

In this video I will tell you How to create a calculator using javascript very easily.

#how to build a simple calculator in javascript #how to create simple calculator using javascript #javascript calculator tutorial #javascript birthday calculator #calculator using javascript and html

JavaScript Map, Reduce, and Filter: What, Why and How to use it

JavaScript Map, Reduce, and Filter - Explained with Examples

Map, reduce, and filter are all array methods in JavaScript. Each one will iterate over an array and perform a transformation or computation. Each will return a new array based on the result of the function. In this article, you will learn why and how to use each one.

Here is a fun summary by Steven Luscher:

var new_array = arr.map(function callback(element, index, array) {
    // Return value for new_array
}[, thisArg])

const numbers = [1, 2, 3, 4];
const doubled = numbers.map(item => item * 2);
console.log(doubled); // [2, 4, 6, 8]

var new_array = arr.filter(function callback(element, index, array) {
    // Return true or false
}[, thisArg])

const numbers = [1, 2, 3, 4];
const evens = numbers.filter(item => item % 2 === 0);
console.log(evens); // [2, 4]

const students = [
  { name: 'Quincy', grade: 96 },
  { name: 'Jason', grade: 84 },
  { name: 'Alexis', grade: 100 },
  { name: 'Sam', grade: 65 },
  { name: 'Katie', grade: 90 }
];

const studentGrades = students.filter(student => student.grade >= 90);
return studentGrades; // [ { name: 'Quincy', grade: 96 }, { name: 'Alexis', grade: 100 }, { name: 'Katie', grade: 90 } ]

arr.reduce(callback[, initialValue])

const numbers = [1, 2, 3, 4];
const sum = numbers.reduce(function (result, item) {
  return result + item;
}, 0);
console.log(sum); // 10

var pets = ['dog', 'chicken', 'cat', 'dog', 'chicken', 'chicken', 'rabbit'];

var petCounts = pets.reduce(function(obj, pet){
    if (!obj[pet]) {
        obj[pet] = 1;
    } else {
        obj[pet]++;
    }
    return obj;
}, {});

console.log(petCounts); 

/*
Output:
 { 
    dog: 2, 
    chicken: 3, 
    cat: 1, 
    rabbit: 1 
 }
 */

#JavaScript #WebDev #javascript