JAVASCRIPT

reduce() break

[ 1, 2, 3, 4, 5].reduce((sum, el, _, arr) => {
  if (el === 4) {
    arr.length = 0;//Array passed to callback is now empty

    return sum;
  }

  return sum + el;
}); // return 1 + 2 + 3 = 6

javascript - How to early break reduce() method?

const array = ['apple', '-pen', '-pineapple', '-pen'];
const x = array
    .slice(0)                         // create copy of "array" for iterating
    .reduce((acc, curr, i, arr) => {
       if (i === 2) arr.splice(1);    // eject early by mutating iterated copy
       return (acc += curr);
    }, '');

console.log("x: ", x, "
original Arr: ", array);
// x:  apple-pen-pineapple
// original Arr:  ['apple', '-pen', '-pineapple', '-pen']