title: Use onFocus on a div with React and Typescript
body: <p>I can not figure out how to use the Focus event with React and Typescript:</p>
  <pre><code>private onFocus(event: FocusEvent) {
  
  }
  
  ...
  
  &lt;div
    tabIndex={0}
    onFocus={this.onFocus}
  &gt;
   Element
  &lt;/div&gt;
  </code></pre>
  <p>With the code above I get the following error</p>
  <blockquote>
  <p>Types of property 'onFocus' are incompatible.</p>
  <p>Type '(event: FocusEvent) =&gt; void' is not assignable to type '((event: FocusEvent) =&gt; void) | undefined'.</p>
  <p>Type '(event: FocusEvent) =&gt; void' is not assignable to type '(event: FocusEvent) =&gt; void'.</p>
  <p>Types of parameters 'event' and 'event' are incompatible.</p>
  <p>Type 'FocusEvent' is not assignable to type 'FocusEvent'.</p>
  <p>Property 'initFocusEvent' is missing in type 'FocusEvent'.</p>
  </blockquote>
  <p>I tried a bunch of approaches to try to make the Typescript compiler happy but nothing seems to work.</p>