Javascript not functioning after adding two variables

Question

Ok, I have these input boxes.

<input 
   type="text" 
   name="amount" 
   class="validate[required] text-input" 
   id="amount">

<input type="text" 
       name="incfee" 
       id="incfee" 
       readonly>

And this is the javascript I have :-

  <script type="text/javascript">
     window.onload = function() {
        var amount = document.getElementById('amount');
        var incfee = document.getElementById('incfee');

        var fee = 0.01;

        amount.onkeyup = function() {
           var result = parseFloat(amount.value) * fee;
           // var result1 = result + amount;
           incfee.value = !isNaN(result) ? result : '';
        };
     }
  </script>

Now, the problem is, that if I comment the line "var result1 = result + amount;" and rename result1 to result in incfee.value , the value of the textbox (amount including fee) changes with the value in amount and everything works fine. BUT, If I uncomment the line var result1 = result + amount; and change result to result 1 in incfee.value, the javascript doesn't works and no value is populated in the incfee textbox. What mistake am I doing? Thanks.

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J0e3gan
– J0e3gan

2014-01-17 16:07:10 +00:00
Commented Jan 17, 2014 at 16:07 — J0e3gan
– J0e3gan, Commented Jan 17, 2014 at 16:07
@J0e3gan This would most likely not result in an error.

JLRishe
– JLRishe

2014-01-17 16:10:16 +00:00
Commented Jan 17, 2014 at 16:10 — JLRishe
– JLRishe, Commented Jan 17, 2014 at 16:10

NaCl · Accepted Answer · 2014-01-17 16:09:59Z

8

var result1 = result + parseFloat(amount.value);

Javacript doesnt know how to add a float and an input-object.

edited Jan 17, 2014 at 16:09

answered Jan 17, 2014 at 16:04

NaCl

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6 Comments

georg Over a year ago

It actually does, but the result might be surprising.

talemyn Over a year ago

Don't forget to convert that value, or you're gonna get a string concatenation.

Brandon Over a year ago

I like learning about math with non-numbers. I'm curious to know what a float + HTMLInputElement equals.

JLRishe Over a year ago

Might want to simplify those two lines to var result1 = amount.value * (1 + fee); and skip the intermediate step (and all the parseFloats.

talemyn Over a year ago

@Brandon - let's say the result equaled 0.01 . . . the "float + HTMLInputElement" computation would net the following string: "0.01[object HTMLInputElement]"

|

CesarMiguel · Accepted Answer · 2014-01-17 16:04:56Z

1

Use .value to get value of input text

var amount = document.getElementById('amount').value; 
var incfee = document.getElementById('incfee').value;

answered Jan 17, 2014 at 16:04

CesarMiguel

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1 Comment

JLRishe Over a year ago

While you've got the right idea, simply modifying these two lines as you've shown would just further break his code.

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