Javascript replace() with $1

Question

Input string is "thisIsSpinalTap". I replaced each uppercase letter with it's lowercase version. I also wanted to add a - before the letter to get the spinal case effect "this-is-spinal-tap".

I wrote the following line of code:

str = str.replace(/([A-Z])/g, '-').toLowerCase();

This replaced each uppercase letter with - to produce "this-s-pinal-ap". This was not the desired effect.

I read that using $1 could produce the effect I wanted, and it did.

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

How does the $1 work to append - to the string, rather than replace the uppercase letter?

developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — SLaks
– SLaks, Commented Mar 28, 2016 at 0:48

Moishe Lipsker · Accepted Answer · 2016-03-28 00:50:55Z

3

$1 is the first group captured in the regular expression.

So in this case, -$1 will replace what was matched with -, followed by the uppercase letter captured in ([A-Z]).

answered Mar 28, 2016 at 0:50

Moishe Lipsker

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