twitter javascript共享出现错误

以下是我的twitter共享javascript代码

(function(){
    window.twttr = (function (d, s, id) {
        var t, js, fjs = d.getElementsByTagName(s)[0];
        if (d.getElementById(id)) return;
        js = d.createElement(s); js.id = id;
        js.src= "https://platform.twitter.com/widgets.js";
        fjs.parentNode.insertBefore(js, fjs);
        return window.twttr || (t = { _e: [], ready: function (f) { t._e.push(f) } });
    }(document, "script", "twitter-wjs"));

    twttr.ready(function (twttr) {
        twttr.events.bind('tweet', function (event) { 
            console.log('backshare');//redirect to your url  } );
        });
    });
})(jQuery);

在这段代码中我得到的javascript错误如下

Uncaught TypeError: Cannot read property 'ready' of undefined 

此链接中出现此错误

twttr.ready(function (twttr) {

请帮忙

多谢各位