crappy lock mechanism for js, "minor projects"

async lock.js

function deferred() {
   let r;
   let p = new Promise(a => r = a);
   p.r = r;
   return p;
}
function lock() {
  let queue = [];
  let locked = false;
  return {
     lock() {
        if(locked) {
           let q = deferred();
           queue.push(q);
           return q;
        }

        locked = true;
     },
     
     unlock() {
       if (!locked) throw new Error('already unlocked');
       
       if(queue.length > 0) {
		let q = queue.shift();
        q.r();
       } else {
        locked = false;
       }
     }
       
  }
}

example.js

let s = lock();

for(let i = 0; i<5; i++) {
  (async () => { 
    try {
       console.log('trigger' + i);
       await s.lock();
       console.log('lock' + i);

       await new Promise(resolve => setTimeout(resolve, 1000 + Math.random() * 5000));

    } finally {
       console.log('unlock' + i);
       s.unlock();
    }
  })();
}

/*
trigger0
trigger1
trigger2
trigger3
trigger4
lock0
...
unlock0
lock1
...
unlock1
lock2
...
unlock2
lock3
...
unlock3
lock4
...
unlock4
*/