JavaScript reduce() Method |

Example

Calculate the sum of all array elements:

var numbers = [65, 44, 12, 4];
function getSum(total, num) {
    return total + num;
}
function myFunction(item) {
    document.getElementById("demo").innerHTML = numbers.reduce(getSum);
}

Output:

125

Try it yourself »

---

Definition and Usage

The reduce() method executes a provided function for each value of the array (from left-to-right).

The reduce() method can be used as a higher-order function for function composition.

Note: The reduce() method does not execute the callback function for empty arrays.

---

Browser Support

The numbers in the table specify the first browser version that fully supports the method.

Method	Chrome	Edge	Firefox	Safari	Opera
reduce()	Yes	9.0	3.0	4	10.5

---

Syntax

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

Parameters

Parameter	Description
function(total, currentValue, index, arr)	Required. A function to execute on each element. Function parameters: Parameter Description total Required. The initial value, or the return value from the previous iteration. currentValue Required. 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.

---

Technical Details

Return Value:	The calculated result.
JavaScript Version:	ECMAScript 3

More Examples

Example

Calculate the sum of array elements after rounding:

Click me

Sum of array elements:

var numbers = [15.5, 2.3, 1.1, 4.7]; function getSum(total, num) { return total + Math.round(num); } function myFunction(item) { document.getElementById("demo").innerHTML = numbers.reduce(getSum, 0); }

Try it yourself »

---

JavaScript and HTML DOM Reference