Make Array Flat Again!

main.js

var result = [];

function flatten(val) {
  if (Array.isArray(val)) {
    for (var i = 0; i < val.length; i++) {
      flatten(val[i]);
    }
  } else {
    result.push(val);
  }
}

var arr = [1, 2, [3, 4, [5, 6, 7]]];
flatten(arr);

console.log(result);