2019-05-13_addition of two numbers

<!DOCTYPE html>
<html lang="en">
  <head>
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    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
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    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.5/css/bootstrap.min.css">

    <script type="text/javascript">
      function calculate()
      {
        event.preventDefault();
        var x1 = parseFloat(document.getElementById("x1").value);
        var x2 = parseFloat(document.getElementById("x2").value);

        var y = x1 + x2;

        document.getElementById("result").innerHTML = y;
      }
    </script>

    <script type="text/javascript">
    function fillRandom() {
       document.getElementById("x1").value = Math.floor(Math.random() * 100);
       document.getElementById("x2").value = Math.floor(Math.random() * 100);
    }
    </script>

  </head>
  <body onload="fillRandom()">

    <div style="padding: 50px;">
          <center><h3 style="padding: 50px;">Javascript Addition example</h3></center>

    <div class="row">
      <div class="col-xs-2">
        <form>
          <div class="form-group">
            <label for="x1">First Number : </label>
            <input type="number" class="form-control" id="x1" placeholder="First number">
          </div>
          <div class="form-group">
            <label for="x2">Second Number : </label>
            <input type="number" class="form-control" id="x2" placeholder="Second number">
          </div>
          <button class="btn btn-default" onClick="calculate()">Calculate</button>
          <input type="button" class="btn btn-info" value="Refresh" onClick="javascript: history.go(0)">
        </form>

        <div class="resultCover" style="padding: 50px;">
            Result : <span id="result"></span>
        </div>
      </div>
    </div>

  </div>

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  </body>
</html>