Javascript giving NaN error

Question

I am using the below codes:

<script type="text/javascript">
function minus(){
var t=document.getElementById("totalcost").value;
var u=document.getElementById("advpay").value;  
var set=(t-u);
document.getElementById("textfield").value=set;
return true;
}
</script>

I entered "6000" as value in totalcost id field and "1000" in advpay id field. so in textfield id field, it should show 5000 (6000-1000), but it is giving answer as NaN. where is the error ?

score 5 · Answer 1 · edited May 23 '17 at 11:56

5

<script type="text/javascript">
function minus() {
    var t = parseInt(document.getElementById("totalcost").value, 10),
        u = parseInt(document.getElementById("advpay").value, 10),
        set = (t - u);
    document.getElementById("textfield").value = set;
    return true;
}
</script>

This is happening because you are trying to subtract two strings! value returns the string of the input, you need to parse it to a number in order to subtract them. Remember to specify radix of parseInt, otherwise the number could be parsed not as a decimal. See this answer for more detailed informations.

edited May 23 '17 at 11:56

Community

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answered Jun 18 '13 at 19:44

Niccolò Campolungo

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"Remember to specify radix of parseInt, otherwise the number will be parsed as an octal." I don't think so... – Jonathan Jun 18 '13 at 19:49
You are right, it will not be parsed as an octal, it will be parsed basically on the number itself. – Niccolò Campolungo Jun 18 '13 at 19:50
"_... otherwise the number will be parsed as an octal_ **IF it begins with a zero.**" – jahroy Jun 18 '13 at 20:03
You commented now, I have modified the answer 15 minutes ago... Is the update wrong? – Niccolò Campolungo Jun 18 '13 at 20:07
No, your correction is good. My comment was just meant to clarify _when_ numbers _can_ get interpretted as octals. – jahroy Jun 19 '13 at 01:33

score 0 · Answer 2 · edited Nov 30 '17 at 12:52

NaN is abbreviated of Not a Number. NaN will be the result of any calculation which contains anything rather than a number (strings, boolean, object). In your case the calculations were made by using 2 strings, That's why it has returned NaN. You have to cast your values into number before doing the calculation.

You can cast your values by using the following piece of code:

Example 1:

 var t = +document.getElementById("totalcost").value;
 u = +document.getElementById("advpay").value;

Example 2 (As @LightStyle suggested):

 var t = parseInt(document.getElementById("totalcost").value, 10),
 u = parseInt(document.getElementById("advpay").value, 10),

Javascript giving NaN error

2 Answers2