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NaN is incredibly useful, but I'm not so sure that 1/"a" = NaN is a great idea.

Strings that arent numeric are type coerced into NaN. Using unary plus to coerce to number: +"2" is the primitive number 2 while +"a" is NaN and per the floating point spec, any arithmetic operation on NaN results in NaN.

The correct though unintuitive way to check for NaN is `(x === x) === false`. NaN is a number per the IEEE 754.

The majority of Javascript WTFs are due to type coercion. Use triple equals and check your inputs to avoid.

No, the correct way is to use the global function isNaN(x);

isNaN will return true for NaN and all values that coerce to it. The equals check will test ONLY for NaN itself:

var x = "a";

isNaN(x); // true

(x === x) === false // false

x = NaN

isNaN(x); // true

(x === x) === false // true

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