"Synchronous" serialport (or whatever) read-write with process queue

//Found at : http://stackoverflow.com/questions/23684802/node-js-serialport-synchronous-write-read

function Device (serial) {
    this._serial = serial;
    this._queue = queue;
    this._busy = false;
    this._current = null;
    var device = this;
    serial.on('data', function (data) {
        if (!device._current) return;
        device._current[1](null, data);
        device.processQueue();
    });
}

Device.prototype.send = function (data, callback) {
    this._queue.push([data, callback]);
    if (this._busy) return;
    this._busy = true;
    this.processQueue();
};

Device.prototype.processQueue = function () {
    var next = this._queue.shift();

    if (!next) {
        this._busy = false;
        return;
    }

    this._current = next;
    this._serial.write(next[0]);
};