JavaScrip如果基于url实现图片下载

function downFile(content, filename) {
  // 创建隐藏的可下载链接
  var eleLink = document.createElement('a');
  eleLink.download = filename;
  eleLink.style.display = 'none';
  // 字符内容转变成blob地址
  var blob = new Blob([content]);
  eleLink.href = URL.createObjectURL(blob);
  // 触发点击
  document.body.appendChild(eleLink);
  eleLink.click();
  // 然后移除
  document.body.removeChild(eleLink);
};

// if (typeof(download.iframe) == 'undefined') {
      //   var iframe = document.createElement('iframe');
      //   download.iframe = iframe;
      //   document.body.appendChild(download.iframe);
      // };
      // download.iframe.src = newdownloadUrl;
      // download.iframe.style.display = "none";

// var $eleForm = $("<form method='get'></form>");
      // $eleForm.attr("action", "https://codeload.github.com/douban/douban-client/legacy.zip/master");
      // $eleForm.attr("action", url);
      // $(document.body).append($eleForm);
      // $eleForm.submit();

downloadIamge(imgsrc, name) {//下载图片地址和图片名
 let image = new Image();
 // 解决跨域 Canvas 污染问题
 image.setAttribute("crossOrigin", "anonymous");
 image.onload = function() {
  let canvas = document.createElement("canvas");
  canvas.width = image.width;
  canvas.height = image.height;
  let context = canvas.getContext("2d");
  context.drawImage(image, 0, 0, image.width, image.height);
  let url = canvas.toDataURL("image/png"); //得到图片的base64编码数据
  let a = document.createElement("a"); // 生成一个a元素
  let event = new MouseEvent("click"); // 创建一个单击事件
  a.download = name || "photo"; // 设置图片名称
  a.href = url; // 将生成的URL设置为a.href属性
  a.dispatchEvent(event); // 触发a的单击事件
 };
 image.src = imgsrc;
},

var a = document.createElement('a');
var url = window.URL.createObjectURL(blob);
var filename = 'what-you-want.txt';
a.href = url;
a.download = filename;
a.click();
window.URL.revokeObjectURL(url);

fetch('http://somehost/somefile.zip').then(res => res.blob().then(blob => {
var a = document.createElement('a');
var url = window.URL.createObjectURL(blob);
var filename = 'myfile.zip';
a.href = url;
a.download = filename;
a.click();
window.URL.revokeObjectURL(url);
}))

fetch('http://somehost/check-permission', options).then(res => {
if (res.code === 0) {
var a = document.createElement('a');
var url = res.data.url;
var filename = 'myfile.zip';
a.href = url;
a.download = filename;
a.click();
} else {
alert('You have no permission to download the file!');
}
});