title: How does a mutable array works in js?
body: <p>i'm Learning Javascript from multiple ressources like FCC where i can't Understand one concept with the mutable arrays. I've got an example :</p>
  
  <pre><code>var myArray = [1,2,3];
  myArray[0]=3;  //[3,2,3]
  
  var ourArray = [1,2,3];
  ourArray[1] = 3; //[1,3,3]
  </code></pre>
  
  <p>i can't get how the <code>[3,2,3]</code> and <code>[1,3,3]</code> are created.</p>
  
  <p>thanks for your help</p>
  
  <p>ok, got it but what if my code looks like this : </p>
  
  <pre><code>var arr = [ [1,2,3], [4,5,6], [7,8,9], [[10,11,12], 13, 14] ];
  arr[3];  // equals [[10,11,12], 13, 14] arr[3][0]; // equals [10,11,12]
  arr[3][0][1]; // equals 11 how the arr[3] or arr[3][0] work ?
  </code></pre>