Yeah, I'm having the same issue when inputing 0

borkaogonyok: Use spoiler flag next time.

80/1.8^2 != (80/1.82)^2

Your formula is not a valid formula for BMI. BMI for 80kg and 1.8m is ~24.7, which is in range of "Normal".

Just as stated in description, with empty string as input, result should be true.

Don't use chained methods when debugging your code, use simple loops, see why your code fails, and only then try to use them.

Not a suggestion. You need to return N-th power, not a square.

your function returnsundefined, it should return a string
if you look at your error messages they probably tell you this

Read this paragraph of FAQ.

With what you provided, no.

You can try providing input that fails, expected output and your output, OR provide your code.

Sure... Maybe check for trailing whitespace.

I just told you your solution fails on empty string, not 0. Weird behaviour for isNaN, but hey that's JS :P

Also, you got to mark your posts with spoiler flag when posting code snippets.