Spinal Tap Case -- Help

Tell us what’s happening:


Can you please explain the below regular expressions because I don’t understand them.

str = str.replace(/([a-z])([A-Z])/g, '$1 $2');

return str.toLowerCase().split(/(?:_| )+/) .join('-');


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Link to the challenge:

In the first line, we are looking for any lowercase characters [a-z] followed by any uppercase characters [A-Z], the () are there to captures the matches, ie what would be interpreted as the $1 and $2 in the second argument for replace, in this case we’re adding a space between them.

In the second line were are splitting the string whenever we encounter an underscore (_) or (|) a space, one or more times (+), and joining the splits with a dash (-) effectively replacing the matches with -s.
the (?: ) part is a non capturing group, because we don’t need the matches like in he first line.

Thanks a lot for your very detailed reply. I have understood everything except the ($1 $2) and the (?: ).

you’re welcome, sorry for the late reply. you can think of them as placeholders. Hope that helps.