javascript - How to early break reduce() method?

Question

How can I break the iteration of reduce() method?

for:

for (var i = Things.length - 1; i >= 0; i--) {
  if(Things[i] <= 0){
    break;
  }
};

reduce()

Things.reduce(function(memo, current){
  if(current <= 0){
    //break ???
    //return; <-- this will return undefined to memo, which is not what I want
  }
}, 0)

Answer 1

UPDATE

Some of the commentators make a good point that the original array is being mutated in order to break early inside the .reduce() logic.

Therefore, I've modified the answer slightly by adding a .slice(0) before calling a follow-on .reduce() step, yielding a copy of the original array. NOTE: Similar ops that accomplish the same task are slice() (less explicit), and spread operator [...array] (slightly less performant). Bear in mind, all of these add an additional constant factor of linear time to the overall runtime + 1*(O(1)).

The copy, serves to preserve the original array from the eventual mutation that causes ejection from iteration.

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']