Jquery选择器长度返回0

这是我的代码，当我运行$fullScreenEl length return zero代码时，我不明白为什么。如果从（函数（$）{}（jQuery）移动文档准备就绪；然后，$（'.full screen'）.lengh返回1。有人能给我提些建议吗

这样更改：

var app = app || {};

(function ($) {
    app.initialize = {
        init: function () {
            app.initialize.fullScreen();
        },
        fullScreen: function () {
            var scrHeight = $window.height();
            console.log($fullScreenEl.length);
            $fullScreenEl.css('height', scrHeight);
        }
    };

    app.documentOnReady = {
        init: function () {
            app.initialize.init();
        }
    };


    var $window = $(window),
        $fullScreenEl = $('.full-screen');

    $(document).ready(app.documentOnReady.init);

})(jQuery);

---

文档准备好后，您必须选择元素。另外，通过将

$window

和

$fullScreenEl

移动到

全屏

函数内部，性能会更好，因为在范围外访问变量要比在同一范围内访问变量慢。

您正在

就绪

处理程序外部初始化

$fullScreenEl

。

(function ($) {
    app.initialize = {
        init: function () {
            app.initialize.fullScreen();
        },
        fullScreen: function () {

           var $window = $(window),
               $fullScreenEl = $('.full-screen');

            var scrHeight = $window.height();
            console.log($fullScreenEl.length);
            $fullScreenEl.css('height', scrHeight);
        }
    };

    app.documentOnReady = {
        init: function () {
            app.initialize.init();
        }
    };


    $(document).ready(app.documentOnReady.init);

})(jQuery);