title: Cannot create observable from Observable.bindNodeCallback(fs.readFile) in TypeScript
body: <p>I am trying to use <a href="https://github.com/ReactiveX/RxJS" rel="noreferrer">rxjs 5</a> to write a Node.js server in TypeScript, but I hit an error when converting <code>fs.readFile</code> to its rxjs form. I expect the following code would work in TypeScript</p>
  
  <pre><code>// This is a JavaScript example from the official documentation. It should
  // also work at the TypeScript envrionment.
  
  import * as fs from 'fs';
  import { Observable } from 'rxjs';
  
  let readFileAsObservable = Observable.bindNodeCallback(fs.readFile);
  
  // This is the line that throws the error.
  let result = readFileAsObservable('./roadNames.txt', 'utf8');
  
  result.subscribe(x =&gt; console.log(x), e =&gt; console.error(e));
  </code></pre>
  
  <p>However, my editor reports a TypeScript error when I add the second parameter <code>'utf-8'</code></p>
  
  <pre><code>Supplied parameters do not match any signature of call target.
  </code></pre>
  
  <p>I try to find a guide on how to use the <code>fs.readFile()</code> in rxjs and TypeScript but there isn't much luck.</p>