title: FileReader readAsText() async issues?
body: <p>I have implemented the following code to parse a CSV via a <code>&lt;input type="file" /&gt;</code> selection:</p>
  
  <pre><code>export async function parse(file: File) {
    let content = '';
    const reader = new FileReader();
    reader.onload = function(e: any) {
      content = e.target.result;
    };
    await reader.readAsText(file);
    const result = content.split(/\r\n|\n/);
    return result;
  }
  </code></pre>
  
  <p>If I run this code and put a breakpoint on the line where I declare <code>result</code>, it retrieves the contents of the file successfully.  If I do not put any breakpoint, the content is empty.  As you can see, I added <code>await</code> to the line where the reader reads the file as text, but it's still not working.</p>