title: How the parameters of callback function work in javascript nodejs
body: <p>When we call an asynchronous function if we can pass a callback function with parameters. I am unable to understand that do I need to memorize the order of the parameter in the call back function. 
  e.g in express </p>
  
  <pre><code>app.get('/',function(req,res))
  </code></pre>
  
  <p>How to know the number of the parameters and the what they contain because I watched a tutorial and I know first req and then res.</p>