title: Add two textbox values and display the sum in a third textbox automatically
body: <p>I have assigned a task to add two textbox values.I want the result of addition to appear in the 3rd textbox,as soon as enter the values in the first two textboxes,without pressing any buttons.</p>
  
  <p>For eg:In the first textbox i want to enter 450,when i press digit 4 of number '450',then it will be added to the 3rd textbox,any number i press in the first two textboxes,suddenly that changes will be reflected on the third textbox.How can i do this?</p>
  
  <p>Here i write my code call sum() in onkeyup</p>
  
  <pre><code>onkeyup="sum()"
  function sum() {
          var txtFirstNumberValue = document.getElementById('txt1').value;
          var txtSecondNumberValue = document.getElementById('txt2').value;
          var result = parseInt(txtFirstNumberValue) + parseInt(txtSecondNumberValue);
          if(!isNaN(result)){
              document.getElementById('txt3').value = result;
          }
  }
  </code></pre>
  
  <p>This is not working in chrome</p>