js 根据url 转换图片（base64）

function getBase64(url, callback) {
  var Img = new Image(),
    dataURL = '';
  Img.src = url + '?v=' + Math.random();
  Img.setAttribute('crossOrigin', 'Anonymous');
  Img.onload = function() {
    var canvas = document.createElement('canvas'),
      width = Img.width,
      height = Img.height;
    canvas.width = width;
    canvas.height = height;
    canvas.getContext('2d').drawImage(Img, 0, 0, width, height);
    dataURL = canvas.toDataURL('image/jpeg');
    return callback ? callback(dataURL) : null;
  };
}