js下载图片代码片段

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('图片下载完成');
        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);
}