JavaScript - string regex backreferences

Question

You can backreference like this in JavaScript:

var str = "123 $test 123"; str = str.replace(/(\$)([a-z]+)/gi, "$2"); 

This would (quite silly) replace "$test" with "test". But imagine I'd like to pass the resulting string of $2 into a function, which returns another value. I tried doing this, but instead of getting the string "test", I get "$2". Is there a way to achieve this?

// Instead of getting "$2" passed into somefunc, I want "test" // (i.e. the result of the regex) str = str.replace(/(\$)([a-z]+)/gi, somefunc("$2")); 

Answer 1

Like this:

str.replace(regex, function(match, $1, $2, offset, original) { return someFunc($2); }) 

Answer 2

Pass a function as the second argument to replace:

str = str.replace(/(\$)([a-z]+)/gi, myReplace);  function myReplace(str, group1, group2) {     return "+" + group2 + "+"; } 

This capability has been around since Javascript 1.3, according to mozilla.org.