相关疑难解决方法(0)

我想上传图像文件,将它们绘制到画布中,进行更改并将其保存在数据库中.我试图测试canvas image(Pic)返回的base64值,它是空的.但是,当我将canvas(Pic)附加到文档时,我看到了结果.我在这做错了什么？

function handleFileSelect(evt) {
  var files = evt.target.files; // FileList object                
  for (var i = 0, f; f = files[i]; i++) {

    if (!f.type.match('image.*')) {
      continue;
    }
    // read contents of files asynchronously
    var reader = new FileReader();

    // Closure to capture the file information.
    reader.onload = (function(theFile) {
      return function(e) {

        var canvas = document.createElement("canvas");

        var datauri = event.target.result,
          ctx = canvas.getContext("2d"),
          img = new Image();

        img.onload = function() {

          canvas.width = width;
          canvas.height …