AsyncForLoopClientSide.js

class AsyncLoop {
    constructor(length, looper, cb) {
        this.i = -1;
        this.length = length;
        this.looper = looper;
        this.callback = cb;
        this.loop();
    }
    loop() {
        this.i++;
        if (this.i == this.length) {
            if (this.callback) {
                this.callback();
            }
            return;
        }
        setTimeout(function() {
            this.looper(this.i);
        }.bind(this), 0);
    }
    stop() {
        this.i = this.length;
        if (this.callback) {
            this.callback();
        }
    }
}

///////////
// USAGE //
///////////

current_loop = new AsyncLoop(9999, function(i) {
    console.log(i)
    if (i > 20) {
        current_loop.stop();
        return;
    }
    current_loop.loop();
}, function() {
    console.log('All done!');
});