title: Typescript strongly typed key value pair declaration
body: <p>I would like to declare a TypeScript interface for such json structure:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>{ 
  404: function() { alert( "page not found" ); }, 
  400 : function() {...} 
  }</code></pre>
  </div>
  </div>
  </p>
  
  <p>the key is number, and the value is function, do you know how to declare an interface in TypeScript for such data constraints?</p>