JavaScript Variable Name Regex

Question

I'm trying to write a regex that will replace all invalid characters in a JavaScript variable name with underscores (in Java).

What I'm wanting to do is:

String jsVarName = "1inva>idName".replaceAll("[a-zA-Z_$][0-9a-zA-Z_$]", "_");

and end up with a variable named _inva_idName.

What I'm struggling to do is figure out how to make the first character different to the others.

[a-zA-Z_$][0-9a-zA-Z_$] are the characters I want, but I cant figure out to hook them into the correct syntax. I know JS var names can be full unicode, but I only care about about ASCII.

since the title is somewhat confusing, note that a javascript variable name can contain far more charactesr than just 0-9a-zA-Z_$ — phil294
– phil294, Commented Aug 15, 2021 at 15:21

Justin · Accepted Answer · 2013-11-05 05:26:19Z

5

String jsVarName = "1inva>idName".replaceAll("^[^a-zA-Z_$]|[^0-9a-zA-Z_$]", "_");

Note that since \w is [a-zA-Z_0-9], it can be simplified:

String jsVarName = "1inva>idName".replaceAll("^[^a-zA-Z_$]|[^\\w$]", "_")

^[^a-zA-Z_$] matches anything that is not [a-zA-Z_$] and appears at the beginning of the line. | is OR. [^0-9a-zA-Z_$] matches anything that is not [0-9a-zA-Z_$].

See regex tutorial for more info.

edited Nov 5, 2013 at 5:26

answered Nov 5, 2013 at 5:13

Justin

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2 Comments

Fabrício Matté Over a year ago

Oh you were talking in relation with my answer, sorry I'm a little slow atm. I thought the character class after | would also match the beginning of the string without negating the ^ but apparently it works without it.

Fabrício Matté Over a year ago

Oh damn, I didn't realize the first group is contained in the second group. +1 your answer is pretty cleaner.

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