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JS Test #10: null + undefined

coderslang profile image Coderslang: Become a Software Engineer Originally published at learn.coderslang.com on ・1 min read

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What’s the difference between null and undefined in JavaScript? What will be logged to the console?
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In the first line, we evaluate null === null and the result is true.

In the second line, we evaluate undefined === undefined and the result is true once again.

In the third line, however, we need to understand what the result of null + undefined is. For JavaScript, it’s hard to make sense of what it should be, so it evaluates this expression as NaN.

Now, is NaN equal to NaN?

And the answer is - NO.

In JS NaN is the only value that’s not equal to itself.


ANSWER: The output is going to be true, true, and false.

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Discussion (1)

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geminii profile image
Jimmy

Mahbe we can precise a little bit but if you need to check NaN you could use isNaN() function to do it 👍

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