JavaScript’s Array Reduce Method

JavaScript has a few different array methods, each of which is useful for different cases. The Array.reduce() method is one such method. While the reduce() method might seem confusing at first, it’s definitely one that all developers should have in their toolbox. The reduce() method takes an array, performs a set of actions on each element of the array, and reduces it to one single value.

The reduce function takes the following syntax:

array.reduce(reducer, initialValue)

// the initialValue argument is optional

As shown above, the reduce() method takes two arguments: a reducer function and an optionalinitial value. Let’s now dive deeper to see what is actually happening under the hood of this reduce() method.

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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.

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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.

Array.fill():

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];

console.log(testArray.fill("A"));

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"].

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JavaScript Array Methods #9: Array .reduce() Method

The JavaScript Array reduce() method executes a reducer function on each element of the array and returns a single output value. Reduce comes with some terminology such as reducer & accumulator. The accumulator is the value that we end with and the reducer is what action we will perform in order to get to one value.

Syntax:
array.reduce(callback(currentvalue, index, arr), thisArg)

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JavaScript Arrays Tutorial. DO NOT MISS!!!

Learn JavaScript Arrays

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Learn Arrays And Array Methods in JavaScript

In JavaScript, an array is a data structure that contains list of elements which store multiple values in a single variable. The strength of JavaScript arrays lies in the array methods. Array methods are functions built-in to JavaScript that we can apply to our arrays — Each method has a unique function that performs a change or calculation to our array and saves us from writing common functions from scratch.
In this video we are going to learn arrays and array methods like sort(), reverse(), join(), split(), pop(), push(), shift(), unshift(), toString(), delete array, etc…

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