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Question

var image未在alert中定义:(请帮助，非常感谢！

handleBeforeUpload (file, event) {
   var reader = new FileReader();
   reader.readAsDataURL(file);
   reader.onload = (function () {
     var f = reader.result;
   }); 

   var image = f;
   alert(image)

   var photo = {uri: image}

Answer 1

你的f变量在onload函数回调的范围内。在该函数之外定义它，您可以在其中定义读取器变量，因此它将在handleBeforeUpload函数的范围内可用

handleBeforeUpload (file, event) {
   var reader = new FileReader();
   var photo = null;
   reader.readAsDataURL(file);
   reader.onload = (function () {
     f = reader.result;
     photo = { uri: f }
   }); 
}