Problem with conversion from string in calculation

[austingal]

I have been handed over an application that I did not create and am fairly new to javascript. My problem is a simple calculation formVal1 = ((1000000 - formVal3) + formVal2) * .0096 I discovered that + is concatenated when adding strings so I need to convert formVal2 to a number. I've tried several things but nothing works.

Thanks!



</script>

<script language = JavaScript>

function CalculateMWh(formItem1,formItem2,formItem3,formItem4) {

var formVal1 = document.getElementById(formItem1).value;
var formVal2 = document.getElementById(formItem2).value;
var formVal3 = document.getElementById(formItem3).value;
var formVal4 = document.getElementById(formItem4).value;
// if (document.getElementById(formItem1).type != 'hidden')
if (formItem1 == 'P8_STDBY_2_AMT' || formItem1 == 'P8_STDBY_MWH')
{
if (document.getElementById(formItem4).value != 107)
{
formVal1 = ((1000000 - formVal3) + formVal2) * .0096

}
else
{
formVal1 = formVal2-formVal3;
}
}
else
{
formVal1 = formVal2-formVal3;
}
document.getElementById(formItem1).value = formVal1;
if (formVal4 == 'P8_AUX_2_AMT')

{
document.getElementById(formItem4).value = formVal1
}
}</script>

 

[theniteowl]

Just do a subtraction of 0.
If formVal2 is being treated as a string doing this:
formVal2-0 will turn it into a number providing it is a numerical value in that field to begin with.

formVal1 = ((1000000 - (formVal3-0)) + (formVal2-0)) * .0096

Stamp out, eliminate and abolish redundancy!

 

[theniteowl]

Actually, any mathematical function applied to a string value will cause it to type-cast except for +, as in:
a = b + c;

However, you can use the + as a unary operator like this:
a = b + (+c);
which will cause b to type-cast
You could also write it as:
a = b + +c;
The parens around the second example help to make it clear what the operation is doing as well as ensuring the order of operation.

Using unary + is the fastest method but I have always just done a subtraction of zero as it is clearer code for others to read.

You could just as easily do any other mathematical operation that does not affect the value returned like:
a = b - 0;
a = b / 1;
a = b * 1;
All of the examples convert the type without altering the value.


Stamp out, eliminate and abolish redundancy!

 

[trollacious]

While I generally use the format

[b]varname * 1[/b]

for this kind of thing, like one of theniteowl's examples, there's a specific function in Javascript to make sure the variable is treated like an integral number:

[b]parseInt(varname, basenumber);[/b]

formVal1 = ((1000000 - formVal3) + parseInt(formVal2, 10)) * .0096;

There's also a function for floating point numbers that does the same thing:

parseFloat(varname);

Lee

 

[austingal]

thank you so much! That did the trick!