ES6 flatten arbitrary array.js

const input = [[1,2,[3]],4];
const output = [1,2,3,4];

function *flatten(arr) {
  for (value of arr) {
    if (Array.isArray(value)) {
      yield *flatten(value);
    } else {
      yield value;
    }
  }
}

console.log(JSON.stringify([...flatten(input)]) == JSON.stringify(output));