How to escape capture group $N followed by integer when performing JavaScript regular expression replace?

Question

I understand that in JavaScript, you can perform regular expression replace with reference to capture groups like this:

> "Hello World 1234567890".replace(
        /Hello (World) (1)(2)(3)(4)(5)(6)(7)(8)(9)(0)/,
        "What's up $1");
"What's up World"

Which is all good. But what if I want to reference to group 1 then immediately followed by "1". Say I what to see "What's up World1". So I'd write:

> "Hello World 1234567890".replace(
        /Hello (World) (1)(2)(3)(4)(5)(6)(7)(8)(9)(0)/,
        "What's up $11");
"What's up 0"

Of course, in this case, it's referencing to group 11, which is "0", instead of group 1 followed by "1".

How could I resolve this ambiguity?

Answer 1

You can use String#replace with a callback function argument:

str = "Hello World 1234567890";
repl = str.replace(/Hello (World) (1)(2)(3)(4)(5)(6)(7)(8)(9)(0)/, function(r, g) {
      return "What's up " + g + '1';});

//=> What's up World1