title: Array of string toUpperCase() doesn't work
body: <p>I have following string array</p>
  
  <pre><code>let example = ["hello", "what"];
  </code></pre>
  
  <p>I want to convert this array's to this:</p>
  
  <pre><code> ["Hello", "what"];
  </code></pre>
  
  <p>To accomplish that I have following code:</p>
  
  <pre><code>example[0][0] = example[0][0].toUpperCase();
  </code></pre>
  
  <p>When I try to console.log(example), I get</p>
  
  <pre><code>["hello", "what"]
  </code></pre>
  
  <p>What's wrong here? How can I convert first element's first letter to upper case?</p>