记录一个JavaScript下载图片的代码片段

(function (root, factory) {    if (typeof define === 'function' && define.amd) {        // AMD. Register as an anonymous module.        define([], factory);    } else if (typeof exports === 'object') {        // Node. Does not work with strict CommonJS, but        // only CommonJS-like environments that support module.exports,        // like Node.        module.exports = factory();    } else {        // Browser globals (root is window)        root.download = factory();  }}(this, function () {    return function download(data, strFileName, strMimeType) {        var self = window, // this script is only for browsers anyway...            defaultMime = "application/octet-stream", // this default mime also triggers iframe downloads            mimeType = strMimeType || defaultMime,            payload = data,            url = !strFileName && !strMimeType && payload,            anchor = document.createElement("a"),            toString = function(a){return String(a);},            myBlob = (self.Blob || self.MozBlob || self.WebKitBlob || toString),            fileName = strFileName || "download",            blob,            reader;            myBlob= myBlob.call ? myBlob.bind(self) : Blob ;              if(String(this)==="true"){ //reverse arguments, allowing download.bind(true, "text/xml", "export.xml") to act as a callback            payload=[payload, mimeType];            mimeType=payload[0];            payload=payload[1];        }        if(url && url.length< 2048){ // if no filename and no mime, assume a url was passed as the only argument            fileName = url.split("/").pop().split("?")[0];            anchor.href = url; // assign href prop to temp anchor              if(anchor.href.indexOf(url) !== -1){ // if the browser determines that it's a potentially valid url path:                var ajax=new XMLHttpRequest();                ajax.open( "GET", url, true);                ajax.responseType = 'blob';                ajax.onload= function(e){                   download(e.target.response, fileName, defaultMime);                };                setTimeout(function(){ ajax.send();}, 0); // allows setting custom ajax headers using the return:                return ajax;            } // end if valid url?        } // end if url?        //go ahead and download dataURLs right away        if(/^data\:[\w+\-]+\/[\w+\-]+[,;]/.test(payload)){                    if(payload.length > (1024*1024*1.999) && myBlob !== toString ){                payload=dataUrlToBlob(payload);                mimeType=payload.type || defaultMime;            }else{                            return navigator.msSaveBlob ?  // IE10 can't do a[download], only Blobs:                    navigator.msSaveBlob(dataUrlToBlob(payload), fileName) :                    saver(payload) ; // everyone else can save dataURLs un-processed            }                    }//end if dataURL passed?        blob = payload instanceof myBlob ?            payload :            new myBlob([payload], {type: mimeType}) ;        function dataUrlToBlob(strUrl) {            var parts= strUrl.split(/[:;,]/),            type= parts[1],            decoder= parts[2] == "base64" ? atob : decodeURIComponent,            binData= decoder( parts.pop() ),            mx= binData.length,            i= 0,            uiArr= new Uint8Array(mx);            for(i;i<mx;++i) uiArr[i]= binData.charCodeAt(i);            return new myBlob([uiArr], {type: type});         }        function saver(url, winMode){            if ('download' in anchor) { //html5 A[download]                anchor.href = url;                anchor.setAttribute("download", fileName);                anchor.className = "download-js-link";                anchor.innerHTML = "downloading...";                anchor.style.display = "none";                document.body.appendChild(anchor);                setTimeout(function() {                    anchor.click();                    document.body.removeChild(anchor);                    if(winMode===true){setTimeout(function(){ self.URL.revokeObjectURL(anchor.href);}, 250 );}                }, 66);                return true;            }            // handle non-a[download] safari as best we can:            if(/(Version)\/(\d+)\.(\d+)(?:\.(\d+))?.*Safari\//.test(navigator.userAgent)) {                url=url.replace(/^data:([\w\/\-\+]+)/, defaultMime);                if(!window.open(url)){ // popup blocked, offer direct download:                    if(confirm("Displaying New Document\n\nUse Save As... to download, then click back to return to this page.")){ location.href=url; }                }                return true;            }            //do iframe dataURL download (old ch+FF):            var f = document.createElement("iframe");            document.body.appendChild(f);            if(!winMode){ // force a mime that will download:                url="data:"+url.replace(/^data:([\w\/\-\+]+)/, defaultMime);            }            f.src=url;            setTimeout(function(){ document.body.removeChild(f); }, 333);        }//end saver        if (navigator.msSaveBlob) { // IE10+ : (has Blob, but not a[download] or URL)            return navigator.msSaveBlob(blob, fileName);        }        if(self.URL){ // simple fast and modern way using Blob and URL:            saver(self.URL.createObjectURL(blob), true);        }else{            // handle non-Blob()+non-URL browsers:            if(typeof blob === "string" || blob.constructor===toString ){                try{                    return saver( "data:" +  mimeType   + ";base64,"  +  self.btoa(blob)  );                }catch(y){                    return saver( "data:" +  mimeType   + "," + encodeURIComponent(blob)  );                }            }            // Blob but not URL support:            reader=new FileReader();            reader.onload=function(e){                saver(this.result);            };            reader.readAsDataURL(blob);        }        return true;    }; /* end download() */}));// 下载一张图片function downloadImg(url, imgName, fn){    var x=new XMLHttpRequest();    var name = imgName ? (imgName + '.png') : (new Date().getTime() + '.png');    x.open("GET", url, true);    x.responseType = 'blob';    x.onload = function (e) {        download(x.response, name, "image/png" );        console.log('图片下载实现');        if(typeof fn === 'function'){            fn();        }    }    x.send();}// 批量下载function downloadImgBatch(imgArr){    let timer = setInterval(function () {        console.log('imgArr.length', imgArr.length);        if(imgArr.length > 0){            let img = imgArr.shift(0);            downloadImg(img.url, img.name);        }else{            clearInterval(timer);        }    }, 500);}