A very basic JavaScript implementation of a Mutex, using promises

Mutex.js

class Mutex {

    constructor() {
        this.current = Promise.resolve();
    }

    async acquire() {
        let release
        const next = new Promise(resolve => {
            release = () => { resolve(); };
        });
        const waiter = this.current.then(() => release);
        this.current = next;
        return await waiter;
    }

}