JavaScript Array reduce function takes a reducer function and an initial value. Using this function one can aggregate, transform items into a new list etc.

Example

//reduce-example.js

const list = [1,2,3,5,8,13];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

console.log(list.reduce(reducer, 0));

Result

32

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Read more

Array.prototype.reduce() on Mozilla Developer Network.

See also

Array.prototype.reduceRight() on Mozilla Developer Network.