你可以用这个来获取base64图像

You can use this to get base64 image

async function getBase64ImageFromUrl(imageUrl) {
  var res = await fetch(imageUrl);
  var blob = await res.blob();

  return new Promise((resolve, reject) => {
    var reader  = new FileReader();
    reader.addEventListener("load", function () {
        resolve(reader.result);
    }, false);

    reader.onerror = () => {
      return reject(this);
    };
    reader.readAsDataURL(blob);
  })
}

那就这样称呼吧

getBase64ImageFromUrl('your url')
    .then(result => testImage.src = result)
    .catch(err => console.error(err));