title: How to perform case-insensitive in array of arrays in JavaScript?
body: <p>I have an array of arrays. I need to set an array of arrays in a case-insensitive way. How to perform this?</p>
  
  <p>I've got this array and I need to set it to lowercase.</p>
  
  <pre><code>
     var criminals = [
          ["Paul White", "Roger Night, Peter Llong Jr."], 
          ["Roger Fedexer", "Rob Ford, Pete Lord, Roger McWire"],
          ["Paul White Jr.", null],
          ["Red Fortress", "Roger Rabbit, Ross Winter"],
          ["Redford Fort", "Red Strong, Red Fort"]
      ];
  
  </code></pre>
  
  <p>I've tried this </p>
  
  <pre><code>
    var sorted = [];
      for (let i = 0; i &lt; criminals.length; i++) {
          sorted.push(criminals[i].toLowerCase());
  
          console.log(sorted)
     } 
  </code></pre>
  
  <p>But I got the following </p>
  
  <pre><code>TypeError: criminals[i].toLowerCase is not a function
  
  </code></pre>