Or just use the spread operator Math.min(... numbers) instead.

(Ref. https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Spread_operator)

The solution is still invalid because it mutates the original array. The final kata test should have had a guard against that...

Nope that's not the goal. The problem with looking at other people's solutions is that they might be further down the line in expertise. Like Dahlia said, it will become more natural with time.

My coding instructor taught us to try to achieve succinct code in this manner, in sequential order:

1. it works
2. it works well
3. clearly it works well

And ultimately, don't strive to cram everything in one line. I think that's just being silly. Yes it's cool, but a lot of times I'll find a one-liner to be not as human readable as a 3-5 liner. The goal is to strike a good balance between readability and efficiency. (And more lines of code doesn't necessarily mean less efficient code - a nested for loop takes only 5 lines in JavaScript but can be really inefficient.)

In case anyone is wondering (like I was) how Math.min.apply(null, numbers) works, have a read at MDN's documentation for apply() - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/apply