Advanced timer with ability to pause/resume the callback

timer.js

/**
 * Advanced timer with ability to pause/resume the callback.
 * @param {function} callback - Callback to be executed after some delay.
 * @param {number} delay - Delay.
 * @returns {Object} Timer object with useful methods.
 */
var timer = function (callback, delay) {
    var isPaused = true;
    var timer, start, clear, pause, resume;

    clear = function () {
        isPaused = false;
        clearTimeout(timer);
    };
    resume = function () {
        clear();
        isPaused = false;
        start = new Date();
        if (delay >= 0) {
            timer = setTimeout(callback, delay);
        }
    };
    pause = function() {
        clear();
        isPaused = true;
        delay -= new Date() - start;
    };
    return {
        clear: clear,
        resume: resume,
        pause: pause,
        isPaused: function() {
            return isPaused;
        }
    };
}