Stackoverflow post referenced states that switch-immediate (which this is) is actually the fastest.

Also it's eight years old now and js uses a totally different optimizing compiler in 2020.

While it depends on the environment and the specific case, the safest bet for performance nowadays is switch over if-else.

https://jsperf.com/if-switch-lookup-table/113

In High Performance JavaScript, Nicholas Zakas talks about conditionals vs. if-else statements:

As it turns out, the switch statement is faster in most cases when compared to if-else, but significantly faster only when the number of conditions is large. The primary difference in performance between the two is that the incremental cost of an additional condition is larger for if-else than it is for switch. Therefore, our natural inclination to use if-else for a small number of conditions and a switch statement for a larger number of conditions is exactly the right advice when considering performance.

Generally speaking, if-else is best used when there are two discrete values or a few different ranges of values for which to test. When there are more than two discrete values for which to test, the switch statement is the most optimal choice.

https://www.safaribooksonline.com/library/view/high-performance-javascript/9781449382308/ch04s02.html

Why not use .every()

You cannot within .map(), as a return statement just exit the relevant function, in this case the one inside the .map() method.

If that is your goal, you might wish to use something like an ordinary loop, iterating over the array.

It's a ES6 feature, enabled via Babel.

That's great to hear!

It can be found in your profile:
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Actually you should completely ignore the first argument of apply function - in this particular case scope does not matter so 0 seems a good option since it's easiest to type (easier than null).
The reason I use apply in the firt place is to create new array with every value set to "undefined". Unfortunately that's the only way to create new array of length n without any holes and without using loops. You can read more about this here: http://speakingjs.com/es5/ch18.html (section "Function.prototype.apply()").