前端 pdfbase64转图片base64

在前端将pdfbase64转换为图片base64的过程中，可以使用canvas来实现。具体步骤如下：

1. 将pdfbase64转换为blob对象。

function base64ToBlob(base64) {
  var arr = base64.split(',');
  var mime = arr[0].match(/:(.*?);/)[1];
  var bstr = atob(arr[1]);
  var n = bstr.length;
  var u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new Blob([u8arr], {type: mime});
}
var pdfBlob = base64ToBlob(pdfBase64);

2. 将blob对象转换为URL。

var pdfUrl = URL.createObjectURL(pdfBlob);

3. 创建canvas对象并绘制图片。

var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
var img = new Image();
img.onload = function() {
  canvas.width = img.width;
  canvas.height = img.height;
  ctx.drawImage(img, 0, 0);
  var imgBase64 = canvas.toDataURL();
  // do something with imgBase64
};
img.src = pdfUrl;

4. 将图片base64返回给后端。

完整代码如下：

function pdfToImgBase64(pdfBase64) {
  function base64ToBlob(base64) {
    var arr = base64.split(',');
    var mime = arr[0].match(/:(.*?);/)[1];
    var bstr = atob(arr[1]);
    var n = bstr.length;
    var u8arr = new Uint8Array(n);
    while (n--) {
      u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], {type: mime});
  }
  var pdfBlob = base64ToBlob(pdfBase64);
  var pdfUrl = URL.createObjectURL(pdfBlob);
  var canvas = document.createElement('canvas');
  var ctx = canvas.getContext('2d');
  var img = new Image();
  img.onload = function() {
    canvas.width = img.width;
    canvas.height = img.height;
    ctx.drawImage(img, 0, 0);
    var imgBase64 = canvas.toDataURL();
    // do something with imgBase64
  };
  img.src = pdfUrl;
}