Spinal Tap Case - Understand Regex ?=

Tell us what’s happening:

Hello there

I’m having troubles understanding the regex here.

Your code so far

function spinalCase(str) {
  return str.trim().split(/\W|_|(?=[A-Z])/).join('-').toLowerCase();


I was doing something similar on my own, but I had to look the solution for the (?=[A-Z])

The thing is when I use the regex to split a string like .split(/\W|_/), it cut the string when it find the character by removing the character, so in our final string there is no space (or _) left.

So when we put (?=[A-Z]) which I think means “find a character where the next character is a capital letter”. It should for example indicate s,s,l in thisIsSpinalTap, to transform it to something like thi-i-spina-tap
Yet by some magic this one doesn’t delete any character. How lucky, we didn’t want that, but still I don’t understand the reason?

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Link to the challenge:

If you check this using https://regex101.com/ (test the string thisIsSpinalCase to check), it finds between the charachters (and set g in the options using the flag to see all the matches)

Don’t really understand yet the look aheads, but, yes, it matches between the characters