Spinal Tap Case - Understand Regex ?=

JavaScript
1

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();
}

spinalCase("thisIsSpinalTap");

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?

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:63.0) Gecko/20100101 Firefox/63.0.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/spinal-tap-case

2

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