img图片转成base64

利用canvas方法

  var img = "https://img.alicdn.com/bao/uploaded/TB1qimQIpXXXXXbXFXXSutbFXXX.jpg";
  function getBase64Image(img) {
    var canvas = document.createElement("canvas");
    canvas.width = img.width;
    canvas.height = img.height;

    var ctx = canvas.getContext("2d");
    ctx.drawImage(img, 0, 0, img.width, img.height);
    var ext = img.src.substring(img.src.lastIndexOf(".") + 1).toLowerCase();
    var dataURL = canvas.toDataURL("image/" + ext);
    return dataURL;
  }
  var image = new Image();
  image.crossOrigin = 'anonymous';//解决Canvas.toDataURL 图片跨域问题
  image.src = img;
  image.onload = function () {
    var base64 = getBase64Image(image);
    console.log(base64);
  }