const new = original.reduce(function(total, current, index, array), initialValue); code example

Example 1: reduce javascript

/* this is our initial value i.e. the starting point*/
const initialValue = 0;

/* numbers array */
const numbers = [5, 10, 15];

/* reducer method that takes in the accumulator and next item */
const reducer = (accumulator, item) => {
  return accumulator + item;
};

/* we give the reduce method our reducer function
  and our initial value */
const total = numbers.reduce(reducer, initialValue)

Example 2: .reduce mdn

arr.reduce(callback( accumulator, currentValue[, index[, array]] )[, initialValue])