Asynchronous mutex class for lock on callback functions.

AsyncMutex.js

class AsyncMutex {
  constructor() {
    this.acquireQueue = [];
    this.isLocked = false;
  }
  	
  lock(callback) {
    return new Promise(resolveOuter => {
      new Promise(resolveInner => {
        if(this.isLocked) {
          this.acquireQueue.push(resolveInner);
	  
          return;
        }
	
        this.isLocked = true;
	
        resolveInner();
      })
      .then(() => {
        const callbackResults = callback();
	
        ((callbackResults instanceof Promise)
          ? callbackResults
          : Promise.resolve(callbackResults))
        .then(results => {
          this.isLocked = !!this.acquireQueue.length;
		
          (this.acquireQueue.shift() || (() => {}))();
		
          resolveOuter(results);
        });
      });
    });
  }
}