title: for..in or for..of Object keys
body: <p>So my IDE doesn't like when I use a for..in loop to iterate over an object keys. I get a warning:</p>
  
  <blockquote>
    <p>Possible iteration over unexpected (custom / inherited) members, probably missing hasOwnProperty check</p>
  </blockquote>
  
  <p>So I get what it's saying, so in that case would it be better to use something like <code>for (const key of Object.keys(obj))</code> instead of <code>for (const key in obj)</code>?</p>
  
  <p>Are there any real differences between the two, performance-wise?</p>