javascript - Getting NaN when adding variables which consists of another variables - Stack Overflow

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var dml = 30
var dd = parseFloat(document.getElementById("DriverD").value)     <----- Only numbers like 10
var dm = dd-dml

alert((dd - dml) * 0.75)    <----- This works
alert(dm * 0.75)            <----- This returns NaN
alert(typeof(dm))        <----- This show that dm is a Number

I'm not sure why I keep getting NaN. I already tried parseFloat and parseInt but still showing NaN when multiplying a variable (dm) which consists of variables (dd-dml). dm is the result of subtracting dml with dd or 10-30. Please share your solutions.

I'm new here and I need help, please don't troll :) I am trying to add a cost calculator to my website.

var dml = 30
var dd = parseFloat(document.getElementById("DriverD").value)     <----- Only numbers like 10
var dm = dd-dml

alert((dd - dml) * 0.75)    <----- This works
alert(dm * 0.75)            <----- This returns NaN
alert(typeof(dm))        <----- This show that dm is a Number

I'm not sure why I keep getting NaN. I already tried parseFloat and parseInt but still showing NaN when multiplying a variable (dm) which consists of variables (dd-dml). dm is the result of subtracting dml with dd or 10-30. Please share your solutions.

I'm new here and I need help, please don't troll :) I am trying to add a cost calculator to my website.

• javascript
• nan

Share Improve this question Follow edited Dec 19, 2012 at 8:01 Blachshma 17.4k44 gold badges6161 silver badges7373 bronze badges asked Dec 19, 2012 at 3:54 JayJay 66666 gold badges1616 silver badges3131 bronze badges 6

• 1 typeof NaN is also "number", could you alert(dm) instead of the last? – Bergi Commented Dec 19, 2012 at 3:58
• 2 Works for me: jsfiddle/HfCrD – Tim M. Commented Dec 19, 2012 at 4:00
• 6 What is the real value of DriverD element – Shiplu Mokaddim Commented Dec 19, 2012 at 4:01
• DriverD is a textbox and I am using 10 during troubleshooting of this issue. My website is a simple html/javascript site. – Jay Commented Dec 19, 2012 at 4:09
• @user1914656 Can you re-create the problem on JSFiddle or link to a live version we can see? – Phil Commented Dec 19, 2012 at 4:24

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5 Answers 5

Sorted by: Reset to default 1

It seems fine to me.

I want to tell another possible problem: You dont check if document.getElementById("DriverD").value is a number or not. If a user enters a string or other type, it will cause a problem.

Try this

Two operands must be convert to parseFloat

<input type="text:" value="10" id="DriverD" />

var dml = parseFloat(30);
var dd = parseFloat(document.getElementById("DriverD").value);
var dm = dd-dml;
alert(dm * .10);

Result is -.2

The only reason you could get NaN here is that the value of dd is NaN. Because the value of dm is defined as dd - dml and the value of dml is a Number value, 30.

parseFloat() always returns a Number value. The - operator converts its operands to Number only if necessary. So the value of dm must by definition be a Number value.

However, NaN is a Number value (typeof NaN === "number"), and it is "toxic": once an operand is NaN, the result of all following arithmetic operations is NaN.

That means that parseFloat() must have returned NaN, which means that the argument to parseFloat() could not be interpreted as the prefix of a decimal number representation.

One mon reason for that is that the user has typed thousands separators (which are not supported) or a decimal ma while only a decimal point is supported.

Try this one

    var dml = 30;
    var dd = parseFloat(document.getElementById("DriverD").value)   ;  <----- Only numbers like 10
    var dm=0;
    dm = dd-dml;

    alert((dd - dml) * 0.75);    <----- This works
    alert(dm * 0.75);            <----- This returns NaN
    alert(typeof(dm));        <----- This show that dm is a Number

I am a newbie but I think it is the type error, solution:

var someV  = parseInt(document.getElementById("some-v-id").value, 10) || 0,  

parseInt(value, 10) - you know because you used parse float, but two pipes and zero might prevent you from NaN as JavaSrcipt might be treating 0 as a string.

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