Checking for Value “NaN”

Question:
Why does my if statement

if (final == "NaN") {  window.alert("You...are...a...dunce.  Hit reload to try again.");}

fail to detect when final is “NaN”? It always goes straight on to the else part, and then comes back with the answer “Required Percentage: NaN%.”

Answer:
If you put “NaN” in quotes like that, it thinks that you’re trying to compare final to a string. You can’t compare anything to Nan directly; instead, you need to use the built-in isNan() function.

What you want to do is instead say:

if (isNan(final)) {...

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