title: JS foreach loop to update an array element
body: <p>I am currently learning JavaScript.
  And I tried to use a foreach loop to update my elements in an array.
  But the problem is that the "console.log" result always been the same array as before.
  Below is the code. 
  Can anyone help tell the problem?</p>
  
  <pre><code>var test = [12, 929, 11, 3, 199, 1000, 7, 1, 24, 37, 4,
      19, 300, 3775, 299, 36, 209, 148, 169, 299,
      6, 109, 20, 58, 139, 59, 3, 1, 139
  ];
  
  var addNum = function(element,index,array){
      if(element%3===0)
      {
          element += 100;
      }
  };
  
  test.forEach(addNum);
  console.log(test);
  </code></pre>