In javascript, what type is NaN?

The NaN attribute represents a value that is "not a number". This special value occurs because the operation cannot be performed, either because one of its operands is not a number (for example, "abc" / 4), or because the result of the operation is not a number (for example, the divisor is zero).

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First of all, although NaN means "not a number", its type is Number.

console.log(typeof NaN === "number");  // logs "true"

Additionally, NaN is false when compared to anything - even itself:

console.log(NaN === NaN);  // logs "false"

If you want to test whether a number is equal to NaN, you can use value !== value. Will only produce true if the value is equal to NaN. In addition, ES6 provides a new Number.isNaN() function, which is a different function and more reliable than the old global isNaN() function.

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