No idea if this works

asyncratelimiter.js

function AsyncRateLimiter() {
    /* Operation is in progress */
    this.doingThing = false;

    /* Next operation to do after this one */
    this.nextFn = false;
}

AsyncRateLimiter.prototype.submit = function(fn) {
    var instance = this;

    if(!instance.doingThing) {
        instance.doingThing = true;

        function doNext() {
            /* Do the next thing if there is one */
            if(instance.nextFn) {
                var p = instance.nextFn();
                instance.nextFn = null;
                p.then(doNext);
            } else {
                instance.doingThing = false;
            }
        }

        /* Do it immediately */
        fn().then(doNext);

    } else {
        /* Do it next, dropping whatever was there */
        instance.nextFn = fn;
    }
}