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JavaScript Array reduce()

Examples

Subtract all numbers in an array:

const numbers = [175, 50, 25];

document.getElementById("demo").innerHTML = numbers.reduce(myFunc);

function myFunc(total, num) {
  return total - num;
}
Try it Yourself »

Round all the numbers and display the sum:

const numbers = [15.5, 2.3, 1.1, 4.7];
document.getElementById("demo").innerHTML = numbers.reduce(getSum, 0);

function getSum(total, num) {
  return total + Math.round(num);
}
Try it Yourself »

Definition and Usage

The reduce() method executes a reducer function for array element.

The reduce() method returns a single value: the function's accumulated result.

The reduce() method does not execute the function for empty array elements.

The reduce() method does not change the original array.


Syntax

array.reduce(function(total, currentValue, currentIndex, arr), initialValue)

Parameters

Parameter Description
function() Required.
A function to be run for each element in the array.
Reducer function parameters:
total Required.
The initialValue, or the previously returned value of the function.
currentValue Required.
The value of the current element.
currentIndex Optional.
The index of the current element.
arr Optional.
The array the current element belongs to.
initialValue Optional.
A value to be passed to the function as the initial value.

Return Value

The accumulated result from the last call of the callback function.


Browser Support

reduce() is an ECMAScript5 (ES5) feature.

ES5 (JavaScript 2009) fully supported in all browsers:

Chrome IE Edge Firefox Safari Opera
Yes 9-11 Yes Yes Yes Yes