"el" is a parameter of the function that is used in filter, it will save the elements of the array in each iteration of filter, so he uses "el" in the function to have each character in the array. I think he named the parameter "el" because of "element". The reason it maybe look's something weird it's because he use a "function expresion"( function(){} ) instead of a "arrow function"( () => {} )

I totally agree with you. This is where the work is done in an array within an array. I saw a great solution here via replace and regExp

It will be considered part of a word and just stays as it is. But the tasks specifies that the input consists only of letters and (single) spaces.

Not all nested loops are inherintly O(n^2). And it is a case here as I explained here

Who the h..l selected current solution as "Best practice" ? Does anybody measures execution time of the functions in here and resources usage ?
or even READABILITY. Give me a break .

Incredible solution, I was shocked

April fools

good

I never worry about big O when doing these.

Isn't it the whole point of these coding tasks — to find a performant solution (in terms of big O)?

For anyone looking for a simple and easy to understand one line solution, look at my solution

I think that my solution is better and more productive :)

Not sure why this is voted as a clever solution, importing a library for a simple comparison is not a clever idea, it just complicates things, by any scale this is not clever!