JS端基于download.js如何实现图片、视频时直接下载而不是打开预览

/*
    * 使用download.js 强制浏览器下载图片、视频等文件
    * @param {any} url url链接地址
    * @param {any} strFileName 文件名
    * @param {any} strMimeType 文件类型
    * dzl
    * 2020年5月8日
     */
    function downloadfile(url, strFileName, strMimeType) {
      var xmlHttp = null;
      if (window.ActiveXObject) {
        // IE6, IE5 浏览器执行代码
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
      } else if (window.XMLHttpRequest) {
        // IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
        xmlHttp = new XMLHttpRequest();
      }
      //2.如果实例化成功，就调用open（）方法：
      if (xmlHttp != null) {
        xmlHttp.open("get", url, true);
        xmlHttp.responseType = 'blob';//关键
        xmlHttp.send();
        xmlHttp.onreadystatechange = doResult; //设置回调函数
      }
      function doResult() {
        if (xmlHttp.readyState == 4) { //4表示执行完成
          if (xmlHttp.status == 200) { //200表示执行成功
            download(xmlHttp.response, strFileName, strMimeType);
          }
        }
      }
    }

/*
 * 根据文件名的尾缀 返回文件类型
 * @param {any} fileName 文件名
 * dzl
 * 2020年5月9日
 */
function getFileType(fileName) {
  // 后缀获取
  let suffix = '';
  // 获取类型结果
  let result = '';
  try {
    const flieArr = fileName.split('.');
    suffix = flieArr[flieArr.length - 1];
  } catch (err) {
    suffix = '';
  }
  // fileName无后缀返回 false
  if (!suffix) { return false; }
  suffix = suffix.toLocaleLowerCase();
  // 图片格式
  const imglist = ['png', 'jpg', 'jpeg', 'bmp', 'gif'];
  // 进行图片匹配
  result = imglist.find(item => item === suffix);
  if (result) {
    return 'image';
  }
  // 匹配txt
  const txtlist = ['txt'];
  result = txtlist.find(item => item === suffix);
  if (result) {
    return 'txt';
  }
  // 匹配 excel
  const excelist = ['xls', 'xlsx'];
  result = excelist.find(item => item === suffix);
  if (result) {
    return 'excel';
  }
  // 匹配 word
  const wordlist = ['doc', 'docx'];
  result = wordlist.find(item => item === suffix);
  if (result) {
    return 'word';
  }
  // 匹配 pdf
  const pdflist = ['pdf'];
  result = pdflist.find(item => item === suffix);
  if (result) {
    return 'pdf';
  }
  // 匹配 ppt
  const pptlist = ['ppt', 'pptx'];
  result = pptlist.find(item => item === suffix);
  if (result) {
    return 'ppt';
  }
  // 匹配 视频
  const videolist = ['mp4', 'm2v', 'mkv', 'rmvb', 'wmv', 'avi', 'flv', 'mov', 'm4v'];
  result = videolist.find(item => item === suffix);
  if (result) {
    return 'video';
  }
  // 匹配 音频
  const radiolist = ['mp3', 'wav', 'wmv'];
  result = radiolist.find(item => item === suffix);
  if (result) {
    return 'radio';
  }
  // 其他 文件类型
  return 'other';
}

//download.js v4.21, by dandavis; 2008-2018. [MIT] see http://danml.com/download.html for tests/usage
// v1 landed a FF+Chrome compatible way of downloading strings to local un-named files, upgraded to use a hidden frame and optional mime
// v2 added named files via a[download], msSaveBlob, IE (10+) support, and window.URL support for larger+faster saves than dataURLs
// v3 added dataURL and Blob Input, bind-toggle arity, and legacy dataURL fallback was improved with force-download mime and base64 support. 3.1 improved safari handling.
// v4 adds AMD/UMD, commonJS, and plain browser support
// v4.1 adds url download capability via solo URL argument (same domain/CORS only)
// v4.2 adds semantic variable names, long (over 2MB) dataURL support, and hidden by default temp anchors
// https://github.com/rndme/download

(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("&#63;")[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&#63;
		} // end if url&#63;


		//go ahead and download dataURLs right away
		if(/^data:([\w+-]+\/[\w+.-]+)&#63;[,;]/.test(payload)){
		
			if(payload.length > (1024*1024*1.999) && myBlob !== toString ){
				payload=dataUrlToBlob(payload);
				mimeType=payload.type || defaultMime;
			}else{			
				return navigator.msSaveBlob &#63; // IE10 can't do a[download], only Blobs:
					navigator.msSaveBlob(dataUrlToBlob(payload), fileName) :
					saver(payload) ; // everyone else can save dataURLs un-processed
			}
			
		}else{//not data url, is it a string with special needs&#63;
			if(/([\x80-\xff])/.test(payload)){			 
				var i=0, tempUiArr= new Uint8Array(payload.length), mx=tempUiArr.length;
				for(i;i<mx;++i) tempUiArr[i]= payload.charCodeAt(i);
			 	payload=new myBlob([tempUiArr], {type: mimeType});
			}		 
		}
		blob = payload instanceof myBlob &#63;
			payload :
			new myBlob([payload], {type: mimeType}) ;


		function dataUrlToBlob(strUrl) {
			var parts= strUrl.split(/[:;,]/),
			type= parts[1],
			indexDecoder = strUrl.indexOf("charset")>0 &#63; 3: 2,
			decoder= parts[indexDecoder] == "base64" &#63; 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";
 				anchor.addEventListener('click', function(e) {
 					e.stopPropagation();
 					this.removeEventListener('click', arguments.callee);
 				});
				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+)(&#63;:\.(\d+))&#63;.*Safari\//.test(navigator.userAgent)) {
				if(/^data:/.test(url))	url="data:"+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 && /^data:/.test(url)){ // 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() */
}));

//生成一个txt的文件，讲字符串变量 str 的内容放在里面，并完成下载
var str = "hello world可以中文吗？答案：可以的";
download(str, "Text.txt", "text/plain");

//也将生成一个txt文件，和上面的结果是一摸一样
str = "data:text/plain,hello%20world";
download(str, "dlDataUrlText.txt", "text/plain");

//将数组或者json对象写入到文件中
var debug = {hello : "world"};
var blob = new Blob([JSON.stringify(debug, null, 2)]);
download(blob, "dlTextBlob.txt", "text/plain");

var str= "hello world", arr= new Uint8Array(str.length);
str.split("").forEach(function(a,b){
  arr[b]=a.charCodeAt();
});
download( arr, "textUInt8Array.txt", "text/plain" );

//将html页面中的一部分生成单独的 html文档
download(document.body.outerHTML, "dlHTML.html", "text/html");

//给字符串添加标签，或者html片段直接给方法，将会生成对应内容的文件
download(new Blob(["hello world".bold()]), "dlHtmlBlob.html", "text/html");

 //将ajax查询回来的结果，赋值给文件，并下载
$.ajax({
  url: "/download.html",
  success: download.bind(true, "text/html", "dlAjaxCallback.html")
});

//将图片的base64装入到图片中并下载。
download("data:image/gif;base64,R0lGODlhRgAVAIcAAOfn5+/v7/f39////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////yH5BAAAAP8ALAAAAABGABUAAAj/AAEIHAgggMGDCAkSRMgwgEKBDRM+LBjRoEKDAjJq1GhxIMaNGzt6DAAypMORJTmeLKhxgMuXKiGSzPgSZsaVMwXUdBmTYsudKjHuBCoAIc2hMBnqRMqz6MGjTJ0KZcrz5EyqA276xJrVKlSkWqdGLQpxKVWyW8+iJcl1LVu1XttafTs2Lla3ZqNavAo37dm9X4eGFQtWKt+6T+8aDkxUqWKjeQUvfvw0MtHJcCtTJiwZsmLMiD9uplvY82jLNW9qzsy58WrWpDu/Lp0YNmPXrVMvRm3T6GneSX3bBt5VeOjDemfLFv1XOW7kncvKdZi7t/S7e2M3LkscLcvH3LF7HwSuVeZtjuPPe2d+GefPrD1RpnS6MGdJkebn4/+oMSAAOw==", "dlDataUrlBin.gif", "image/gif");

//使用xhr获取本域名下文件，并封装到文件进行下载。这里的前提是xhr访问的文件必须和该程序执行在同一域名下，
//否则会报跨域的问题。比如此程序执行在localhost下面，而这里的访问地址使用的是http://danml.com，就会访问不成功。
  var x=new XMLHttpRequest();
  x.open("GET", "http://danml.com/wave2.gif", true);
  x.responseType = 'blob';
  x.οnlοad=function(e){
    download(x.response, "dlBinAjax.gif", "image/gif" );
  };
  x.send();