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Check if number is NaN in javascript patchG'Day all I was just wondering if anyone knows a clean way to check if a number is NaN. I have tried 4 ways and only one returns true, but its a bit messy. 1/ (This way doesn't work) var testNumber = NaN; if (testNumber == undefined) // This returns false Log("testNumber is NaN"); else Log("testNumber was not detected as NaN)"; 2/ (This way errors) var testNumber = NaN; if (isnan(testNumber)) // This errors as there is no isnan() method Log("testNumber is NaN"); else Log("testNumber was not detected as NaN)"; 3/ (This way doesn't work) var testNumber = NaN; if (testNumber == NaN) // returns false Log("testNumber is NaN"); else Log("testNumber was not detected as NaN)"; 4/ (This way works, but is not clean and makes me sad inside) var testNumber = NaN; var testNumber2 = testNumber  9999; if (testNumber == 9999) // returns true, as wanted. Log("testNumber is NaN"); else Log("testNumber was not detected as NaN)"; Anyone have any ideas? Cheers Lango
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As per IEEE754 spec, a nan checked for equality against itself will be unequal (in other words, nan != nan)
in code, you can exploit this with the following:
(similar techniques work in C)
Nice, thanks for that.
You have an error in the second way because you're using an incorrect function. The correct funcion name must be 'isNaN' (N is uppercase)
When a division by zero occurs, is there any particular reason why the Math patch outputs < inf > as result, but the Mathematical expression < nan > ?
It calls for 2 different tests!
Math outputs inf because that's the correct result (division by zero results in +inf or inf, depending on signs, according to the IEEE754 spec). Expression doesn't because it probably does some internal processing on the output that massages infs into nans (QC doesn't handle nans very well, nor does it handle negative indexes very well  this is a limitation of the Port classes, from my limited experimentation).
You're slightly limiting the isFinite function:
isFinite will return false for NaN and +/inf (because neither of those are finite values). it will return true for all other floating point numbers (+/0, subnormals, etc).
So if you're not really interested in nans specifically, just is isFinite, as it will fail nan and inf.
Sometimes inf is handy because you can still use it in mathematical expressions (most of the time this will kill your results, but there are cases where it's useful).
Like that ;)
var test = NaN;
function checkNaN(n) { return !(n >= 0  n < 0); }
checkNaN(test) => true
checkNaN(12) => false