title: Access object key using variable in typescript
body: <p>In typescript, How to access object key(property) using variable?</p>
  
  <p>for example:</p>
  
  <pre><code>interface Obj {
      a: Function;
      b: string;
  }
  
  let obj: Obj = {
      a: function() { return 'aaa'; },
      b: 'bbbb'
  }
  
  for(let key in obj) {
      console.log(obj[key]);
  }
  </code></pre>
  
  <p>but typescript throw below error message:</p>
  
  <blockquote>
    <p>'TS7017 Element implicitly has an 'any' type because type 'obj' has no index signature'</p>
  </blockquote>
  
  <p>How to fix it?</p>