Flattering Array

flatteting-array.js

// case [[1,2,[3]],4]
// case [[1, 2],[3, 4, 5], [6, 7, 8, 9]];

var array = [[1, 2],[3, 4, 5], [6, 7, 8, 9]];

function flattenArray(value) {
  
  const stack = [...value];
  
  const res = [];
  
  while (stack.length) {
    const next = stack.pop();
    if (Array.isArray(next)) {
      stack.push(...next);
    } else {
      res.push(next);
    }
  }
  
  return res.reverse();
}

flattenArray(array);