title: How do I fix error TS1015: Parameter cannot have question mark and initializer?
body: <p>I have just upgraded to TypeScript beta 0.9 and now I'm getting the error:</p>
  
  <blockquote>
    <p>TS1015: Parameter cannot have question mark and initializer</p>
  </blockquote>
  
  <p>This was valid before, how do I fix this?</p>
  
  <p>Here's an example of the code that's generating this error:</p>
  
  <pre><code>functionName(parameterName?: typeName = defaultValue): typeName
  </code></pre>