arr.reduce in promise.all code example

Example 1: array reduce

arr.reduce(callback( accumulator, currentValue[, index[, array]] ) {
  // return result from executing something for accumulator or currentValue
}[, initialValue]);

Example 2: JavaScript Array Methods .reduce()

const list = [1, 2, 3, 4, 5];
console.log(list.reduce((number, nextNumber) => number + nextNumber));
// --> 15