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null vs undefined vs NaN in JavaScript

What’s the difference between null, undefined and NaN in JavaScript?


null value represents nothing, nonexistent or invalid object or address. It converts to 0 in simple arithmetic operations and it’s global object. null == false gives us false.


The global undefined property represents the primitive value undefined. It tells us something has not assigned value; isn’t defined. undefined isn’t converted into any number, so using it in maths calculations returns NaN.


NaN (Not-A-Number) represents something which is not a number, even though it’s actually a number. It’s not equal to itself and to check if something is NaN we need to use isNaN() function.

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