How to use array reduce in JavaScript

In this article, I am going to explain about reduce method in JavaScript.
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Array reduce method in JavaScript

Reduce method in JavaScript applies one-element arrays are turned into their unique element, while multiple-element array are return  untouched.

Syntax of reduce method

array.reduce(callback[, initalvalue]);

Parameters in reduce method:

  • callback

    Callback function accepts up to four arguments. and it execute on each value in the array.

  • initialvalue

    Initial value object is use as the first argument to the first call of the call back.

Return value in reduce method

It returns an object that contains the accumulated result from the last call to the callback function.

Exception in reduce method

If callback argument is not a function object and array contain no element and initial value is not provide, A TypeError exception is fire.

There are the following callback parameter:

Parameter Value
Previous value The value from previous call to the callback function.
Current value The value of  the current  array element.
Current  index The numeric index of the current array element.

Example of reduce method


<!DOCTYPE html>



<title>JavaScript Array Reduce Method</title>



<script type="text/javascript">

function ReduceMeth(previousValue, currentValue) {

    return previousValue + ":" + currentValue;


var elements = ["Java", "Script", 111, 222];

var result = elements.reduce(ReduceMeth);







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