title: Why event properties are not easy to get?
body: <p>I have following code ( <strong><a href="https://jsfiddle.net/5n2zagjc/2/" rel="nofollow noreferrer">HERE</a></strong> is editable example - usage: type in input field and watch console):</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>function test(event) 
  {   
    let keys = Object.keys(event);
    let keysOwnProp = Object.getOwnPropertyNames(event);
    let keysForIn=[]; for(let k in event) { keysForIn.push(k); }
  
  
    console.log('keysForIn',keysForIn);
    console.log('keys',JSON.stringify(keys));
    console.log('keysOwnProp',JSON.stringify(keysOwnProp));
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;input oninput="test(event)" placeholder="type something"&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><strong>Questions</strong>: </p>
  
  <ul>
  <li>Why only in <code>keysForIn</code> I see all(?) event fields/properties, but in <code>keys</code> and <code>keysOwnProp</code> only one: <code>isTrusted</code>? </li>
  <li>Is there an alternative for <code>keysForIn</code> (if yes, provide it) ?</li>
  </ul>