试图在javascript中调用一个闭包函数

Question

我有一个计时器，我想通过调用

开始

countdownTimer.start(600,'/page2.html');

显示计时器从600秒倒计时后，它将重定向到page2.html

我还想通过调用以下内容来恢复以前的计时器（来自cookie）。我只是使用cookie来保存它停止的值，所以如果刷新页面，它将重新开始计数而不是重新开始。

countdownTimer.resume(123, '/page2.html');

我遇到了各种各样的错误，关于内部html没有被定义（我假设这与函数顶部的变量没有被调用有关）。

有人可以帮我理解如何创建这样的javascript对象吗？它总是困惑我：/

var countdownTimer = (function() {

    var elem = document.getElementById("countdown");
    var url     = '';
    var end     = 60;
    var _second = 1000;
    var _minute = 60000;
    var _hour   = 3600000;
    var timer;

    function pad (n, amount) {
        return n > parseInt(Array(amount).join("9")) ? "" + n : "0" + n;
    }

    function showRemaining () {
        var now = new Date().getTime();
        var distance = end - now;
        if (distance < 0 ) {
            clearInterval( timer );
            elem.innerHTML = "Offer Expired";
            window.location.href = url;
            return;
        }
        var minutes = Math.floor( (distance % _hour) / _minute );
        var seconds = Math.floor( (distance % _minute) / _second );
        var milliseconds = Math.floor( (distance % _second) );

        elem.innerHTML =  pad(minutes, 2) + ' <span>:</span> ';
        elem.innerHTML += pad(seconds, 2) + ' <span>:</span> ';
        elem.innerHTML += pad(milliseconds, 3);
    }

    var start = function (secondsToExpire, url) {
        url = url;
        end = new Date().getTime() + (secondsToExpire * 1000);
        timer = setInterval(showRemaining, 1);
    }

    var resume = function (customEnd, url) {
        url = url;
        end = customEnd;
        timer = setInterval(showRemaining, 1);
    }

    var currentTime = function () {
        return 500;
    }

    return {
        start: start,
        resume: resume,
        currentTime: currentTime
    };
})();