JavaScript Array reduce() Method
The Javascript arr.reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each value of the array (from left to right) and the return value of the function is stored in an accumulator.
Syntax:
array.reduce( function(total, currentValue, currentIndex, arr),
initialValue )
Parameters:
This method accepts five parameters as mentioned above and described below:
- function(total, currentValue, index, arr): It is the required parameter and is used to run for each element of the array. It contains four parameters which are listed below:
- total: It is a required parameter and is used to specify the initial value or the previously returned value of the function.
- currentValue: It is a required parameter and is used to specify the value of the current element.
- currentIndex: It is an optional parameter and is used to specify the array index of the current element.
- arr: It is an optional parameter and is used to specify the array object the current element belongs to.
- initialValue: It is an optional parameter and is used to specify the value to be passed to the function as the initial value.
Return value:
The JavaScript array reduce method returns a single value/element after traversing the complete array.
Below are examples of the Array reduce() method.
Example 1: In this example, we will write a reduce function to simply print the difference of the elements of the array.
Javascript
// Input arraylet arr = [175, 50, 25];// Callback function for reduce methodfunction subofArray(total, num) { return total - num;}//Fucntion to execute reduce method function myGeeks(item) { // Display output console.log(arr.reduce(subofArray));}myGeeks() |
Output
100
Example 2: This example uses reduce() method to return the sum of all array elements.
Javascript
// Input arraylet arr = [10, 20, 30, 40, 50, 60];// Callback function for reduce methodfunction sumofArray(sum, num) { return sum + num;}//Fucntion to execute reduce method function myGeeks(item) { // Display output console.log(arr.reduce(sumofArray));}myGeeks(); |
Output
210
Example 3: This example uses reduce() method to return the round sum of all array elements.
Javascript
// Input arraylet arr = [1.5, 20.3, 11.1, 40.7];// Callback function for reduce methodfunction sumofArray(sum, num) { return sum + Math.round(num);}//Fucntion to execute reduce method function myGeeks(item) { // Display output console.log(arr.reduce(sumofArray, 0));}myGeeks(); |
Output
74
We have a complete list of Javascript Array methods, to check those please go through this Javascript Array Complete reference article.
Supported Browsers: The browsers supported by JavaScript Array reduce() method are listed below:
- Google Chrome
- Microsoft Edge
- Mozilla Firefox
- Safari
- Opera
We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.
