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 »
Description
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.
Note
At the first callback, there is no return value from the previous callback.
Normally, array element 0 is used as initial value, and the iteration starts from array element 1.
If an initial value is supplied, this is used, and the iteration starts from array element 0.
See Also:
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. |
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Reducer function parameters:
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| initialValue | Optional. A value to be passed to the function as the initial value. |
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Return Value
| The accumulated result from the last call of the callback function. |
Array Tutorials:
Browser Support
reduce() is an ECMAScript5 (ES5) feature.
ES5 (JavaScript 2009) is fully supported in all modern browsers since July 2013:
| Chrome 23 |
IE/Edge 11 |
Firefox 21 |
Safari 6 |
Opera 15 |
| Sep 2012 | Sep 2012 | Apr 2013 | Jul 2012 | Jul 2013 |
