function getScreenDPI() {
    if (SCREEN_DPI.length === 0) {
        if (window.screen.deviceXDPI != undefined) {
            SCREEN_DPI.push(window.screen.deviceXDPI);
            SCREEN_DPI.push(window.screen.deviceYDPI);
        } else {
            let tmpNode = document.createElement("DIV");
            tmpNode.style.cssText = "width:1in;height:1in;position:absolute;left:0px;top:0px;z-index:99;visibility:hidden";
            document.body.appendChild(tmpNode);
            SCREEN_DPI.push(parseInt(tmpNode.offsetWidth));
            SCREEN_DPI.push(parseInt(tmpNode.offsetHeight));
            tmpNode.parentNode.removeChild(tmpNode);
        }
    }
    return SCREEN_DPI;
}

function setupDateFormat() {
    Date.prototype.Format = function (fmt) {
        let o = {
            "M+": this.getMonth() + 1, //月份
            "d+": this.getDate(), //日
            "h+": this.getHours(), //小时
            "m+": this.getMinutes(), //分
            "s+": this.getSeconds(), //秒
            "q+": Math.floor((this.getMonth() + 3) / 3), //季度
            "S": this.getMilliseconds() //毫秒
        };
        if (/(y+)/.test(fmt)) fmt = fmt.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length));
        for (let k in o)
            if (new RegExp("(" + k + ")").test(fmt)) fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));
        return fmt;
    };
}

function dynamicLoadJs(url, type, callback) {
    let head = document.getElementsByTagName('head')[0];
    let script = document.createElement('script');
    script.type = 'text/javascript';
    script.src = url;
    if(callback) {
        script.onload = script.onreadystatechange = function (event) {
            callback(type);
            script.onload = script.onreadystatechange = null;
        };
    }
    head.appendChild(script);
}

/**
 * 获取 blob
 * @param  {String} url 目标文件地址
 * @return {Promise}
 */
 function getBlobPublic(url) {
    return new Promise(resolve => {
        const xhr = new XMLHttpRequest();
        xhr.open('GET', url, true);
        xhr.responseType = 'blob';
        xhr.onload = () => {
            if (xhr.status === 200) {
                resolve(xhr.response);
            } else {
                resolve('not found!');
            }
        };
        xhr.send();
    });
}