title: Request defaults, use a function as default header
body: <p>When using the NPM request module's request.defaults API, does anyone know of anyway in which I can pass a function as a request header, so that the function's result becomes the header value everytime I make an outgoing request?</p>
  
  <p>i.e.</p>
  
  <pre><code>request.defaults({
      headers:{datestamp:() =&gt; new Date()
  })
  </code></pre>