Here's a lock implementation I made just barely as a proof of concept:

https://bl.ocks.org/johnsonjo4531/99256568deaf8c0f1685793a4a...

Basically it is used like this:

```

  var lock = new AsyncLock();

  (async () => {
    for await(var _ of lock) {
      console.log("here 1a");
      await sleep(1000);
      console.log("here 1b")
    }
  })();

  (async () => {
    for await(var _ of lock) {
      console.log("here 2a");
      await sleep(1000);
      console.log("here 2b")
    }
  })();

  /*
  When Lock is working should print:
  here 1a
  here 1b
  here 2a
  here 2b
  Without the lock it would print:
  here 1a
  here 2a
  here 1b
  here 2b 
  */

```

If you want to check out the implementation go to the blocks link. (which is basically just a gist that you can run). Here's the actual gist link: https://gist.github.com/johnsonjo4531/99256568deaf8c0f168579....

It requires Chrome 63 (at this point Chrome Canary) because it uses async iterators. I used this because I can close the lock automatically in case an error is thrown, the loop is broken. It only iterates one value and only after the lock is unlocked.