Iterative solution for flattening n-th nested arrays in Javascript

Question

Can anyone show me an iterative solution for the following problem? I solved it recursively but struggled with an iterative solution. (Facebook Technical Interv

Answer 1

A fairly concise, readable algorithm:

function flatten(input) {
  var output = [];
  var todo = [input];
  var current;

  while(todo.length) {
    var current = todo.shift();
    if(Array.isArray(current)) {
       todo.unshift.apply(todo, current)
    } else {
      output.push(current);
    }
  }

  return output;
}

This version performs better than my other answer, but is still significantly slower than James Wilkins' answer.

JSBin

Tomalak's JSPerf