How to do recursion correctly?

Question

JavaScript

There is an object

let entityTree = {
  account: ['account_subscriptions', 'device'],
  device: 'device_subscriptions'
}

If an account comes in, then it should be an array ['account', 'account_subscriptions', 'device', 'device_subscriptions'].

Answer 1

function xxx(key) {
  let val = entityTree[key];
  const nextKey = Array.isArray(val) && (val = [...val], val.pop());
  return val ? [].concat(key, val, xxx(nextKey)) : [];
}