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The JavaScript array reduce() method is used to reduce the elements of an array to a single value. It executes a provided function for each value of the array (from left-to-right). The return value of the function is stored in an accumulator (result/total).

Syntax:

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

Parameters:

function(total, currentValue, currentIndex, arr) – A function to execute on each element in the array.

Parameters of reducer’s function

Example

var arr = [1, 2, 3, 4, 5];

var sum = arr.reduce(function(a, b) {
    return a + b;
});

console.log(sum); // 15