Simple Calculation using JavaScript

Question

I'm trying to create a simple javascript calculation script, but for some reason can't get it work.

  function calculate() {
    var USERINPUT1 = document.TESTING.INPUT1.value,
      RESULT = USERINPUT1 + (USERINPUT1 * .05);
    document.TESTING.OUTPUT1.value = RESULT;
  }

<form name="TESTING">
  <table border="1" width="600" height="200" cellpadding="10" cellspacing="3">
    <tr>
      <th colspan="2">
        <h1>5% TAX CALCULATOR</h1>
      </th>
    </tr>
    <tr>
      <th>
        <h3>ORIGINAL PRICE</h3>
      </th>
      <th>
        <h3>ORIGINAL PRICE + 5% TAX</h3>
      </th>
    </tr>
    <tr>
      <td>
        <input type="number" name="INPUT1" id="input" onchange="calculate();" />
      </td>
      <td>
        <input type="number" name="OUTPUT1" id="output">
      </td>
    </tr>
  </table>
</form>

When I enter 100 into INPUT, the OUTPUT becomes 1005, but it should be 105.

Could you please point out where the mistake is? Thank you!

Nikhil Aggarwal · Accepted Answer · 2015-08-01 10:56:54Z

2

document.TESTING.INPUT1.value returns string. You need to convert into number so as to perform mathematical operations.

Hence, update from

var USERINPUT1 = document.TESTING.INPUT1.value,

to

 var USERINPUT1 = parseFloat(document.TESTING.INPUT1.value),

For reference - http://plnkr.co/edit/kRxK8Kf4fO6N8E9v9D2W?p=preview

answered Aug 1, 2015 at 10:56

Nikhil Aggarwal

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