flatten array

flatten.js

function flatten(original){
  let result = [], temp, child;
  if(Array.isArray(original)){
    temp = original.slice(0)
  } else {
    temp = [original]
  }
  
  while(temp.length){
    if((child = temp.pop()) && child.pop){
      for(let index = 0; index < child.length; index++){
        temp[temp.length] = child[index]
      }
    } else {
      result.unshift(child)
    }
  }
  return result;
}