Free JavaScript course. Sign Up for tracking progress →

JavaScript: NaN

Some operations with infinity, for example, dividing infinity by infinity, return a weird result. In math, this operation has no numerical equivalent. In JavaScript, you'll get NaN.

Infinity / Infinity; // NaN

NaN is a special value, "not a number", that usually indicates execution of a meaningless operation. Any operation with NaN returns NaN.

NaN + 1; // NaN

NaN is a peculiar value. Although it means "not a number", it belongs to the number data type. What a paradox. NaN is never a value you want to see, it appears only as a result of errors. If you come across it, find the point where the operation that wasn't valid for numbers was performed, and correct the piece of code.


Execute the operation that returns NaN and print it using console.log().

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.


If you got stuck and don't know what to do, you can ask a question in our community