When reading a file from client side with Angular2 and Typescript,

I try to use FileReader in this way:

var fileReader = new FileReader();
fileReader.onload = function(e) {
   console.log("run fileReader.onload");
   //  ......
}

But it doesn't work at all, this "fileReader.onload" function will never be called.

Really need a solution for reading files, please help.
If, it's a bug, then, is there any work around for now?

Thanks