var CheckOrientation = (function(){

    var win = $( window ),

        get_orientation,

        last_orientation,

        initial_orientation_is_landscape,

        initial_orientation_is_default,

        portrait_map = { "0": true, "180": true },

        ww, wh, landscape_threshold;

    if(window.orientation !== undefined){

        ww = window.innerWidth || win.width();

        wh = window.innerHeight || win.height();

        landscape_threshold = 50;

        initial_orientation_is_landscape = ww > wh && ( ww - wh ) > landscape_threshold;

        initial_orientation_is_default = portrait_map[ window.orientation ];

        // (初始是横屏，方向是0或者180), *OR*

        // 初始是竖屏，方向是90或者-90, we

        //需要调整portrait_map

        if ( ( initial_orientation_is_landscape && initial_orientation_is_default ) || ( !initial_orientation_is_landscape && !initial_orientation_is_default ) ) {

          portrait_map = { "-90": true, "90": true };

        }

    }

      /**

       * 判断是横竖屏

       * @return {[type]} [description]

       */

    function get_orientation(){

        var isPortrait = true, elem = document.documentElement;

        if ( window.orientation !== undefined ) {

            isPortrait = portrait_map[ window.orientation ];

        } else {

            isPortrait = elem && elem.clientWidth / elem.clientHeight < 1.1;

        }

        return isPortrait ? "portrait" : "landscape";

    }

    last_orientation = get_orientation();

    function handler() {

        var orientation = get_orientation();

        if ( orientation !== last_orientation ) {

            last_orientation = orientation;

            win.trigger('orientation:change',[last_orientation]);//借用zepto的trigger事件

        }

    }

    window.addEventListener("onorientationchange" in window ? "orientationchange" : "resize", handler, false); 

    return {

        get_orientation : get_orientation

    }

})();