JavaScript reduce() function is used with Array to execute a reducer function for the array elements. It returns a single value: the function’s accumulated result.
array.reduce(function(total, currentValue, currentIndex, arr), initialValue)The reduce() does not change the original array.
Example Reduce() function in JavaScript
Simple example code Sum of All Values of Array.
<!DOCTYPE html>
<html>
<body>
<script>
const numbers = [1, 2, 3, 4, 5];
function sum_reducer(accumulator, currentValue) {
return accumulator + currentValue;
}
let sum = numbers.reduce(sum_reducer);
console.log(sum);
// using arrow function
let summation = numbers.reduce(
(accumulator, currentValue) => accumulator + currentValue
);
console.log(summation);
</script>
</body>
</html>
Output:
Round all the numbers and display the sum:
<script>
const numbers = [15.5, 2.3, 1.1, 4.7];
console.log(numbers.reduce(getSum, 0));
function getSum(total, num) {
return total + Math.round(num);
}
</script>Output: 24
Find the maximum value in an array:
const arr = [3, 6, 2, 8, 1, 9];
const max = arr.reduce((accumulator, currentValue) => {
if (currentValue > accumulator) {
return currentValue;
} else {
return accumulator;
}
});
console.log(max); // Output: 9
Comment if you have any doubts or suggestions on this JS reduce topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version