Flatten Array

Without using .flat(), create a function to flatten an array

function flatten(arr) {
 return arr.reduce(function(prev, curr) {
  if (Array.isArray(curr)) {
   prev = prev.concat(flatten(curr));
  } else {
    prev.push(curr);
  }
  return prev;
 }, []);
}

const exampleArray = [1,2,[3,4, [5,6,7], 8], 9, 10];
console.log(flatten(exampleArray)); // [1,2,3,4,5,6,7,8,9,10]