(function() { //閉包
    function load_script(xyUrl, callback) {
        var head = document.getElementsByTagName('head')[0];
        var script = document.createElement('script');
        script.type = 'text/javascript';
        script.src = xyUrl;
        //借鑒了jQuery的script跨域方法
        script.onload = script.onreadystatechange = function() {
            if ((!this.readyState || this.readyState === "loaded" || this.readyState === "complete")) {
                callback && callback();
                // Handle memory leak in IE
                script.onload = script.onreadystatechange = null;
                if (head && script.parentNode) {
                    head.removeChild(script);
                }
            }
        };
        // Use insertBefore instead of appendChild  to circumvent an IE6 bug.
        head.insertBefore(script, head.firstChild);
    }

    function translate(point, type, callback) {
        var callbackName = 'cbk_' + Math.round(Math.random() * 10000); //隨機函數名
        var xyUrl = "http://api.map.baidu.com/ag/coord/convert?from=" + type + "&to=4&x=" + point.lng + "&y=" + point.lat + "&callback=BMap.Convertor." + callbackName;
        //動態創建script標簽
        load_script(xyUrl);
        BMap.Convertor[callbackName] = function(xyResult) {
            delete BMap.Convertor[callbackName]; //調用完需要刪除改函數
            var point = new BMap.Point(xyResult.x, xyResult.y);
            callback && callback(point);
        }
    }

    window.BMap = window.BMap || {};
    BMap.Convertor = {};
    BMap.Convertor.translate = translate;
})();