lowercase 'a' should have been an uppercase 'A'

Why even use fill?
It can be solved in O(n), in a single passage.

uggh i rushed this. i have a better refactored answer submitted

uggh i've refactpred twice. look for my newest version

i should have done more refactoring once i saw that it worked. still new at javascript so didn't occur to use filter or other array functions

i like the test for zero problems and a shift before the for loop. wish i had thought of that

write a simple swap function. also, dont make calls to IndexOf twice in a row for same thing

take a look at my code and see if it helps you

your swapping solution is what i did. take a look at my solution

not clean or maintainable by other team members. clever to cram everything together and i also think the big O performance of this solution will be terrible

but then the check of the 3x3 subgrids will not total 45 they they have to

no need to filter for zeros at the end. you know they are zeros. just pad out the filtered non-zero array with zeros

the filter for the zeros seems wastefull. looks cool but you could have just aray.fill'ed the tail end of zeros.

the details for assignment was to trim the trailing end. you trimmed the leading and trailing end. this would mess up and lines of text that started with spaces