Invalid Regex Group

Question

Can anyone understand why this gives an error Invalid regular expression: Invalid group?

text.replace(/(?<!br|p|\/p|b|\/b)>/g, "&gt;");

This is normal:

text.replace(/<(?!br|p|\/p|b|\/b)/g, "&lt;");

So I'm not sure where I am wrong in the first ( >).

Here's a fiddle with an example.

+3

Paul May 21 '12 at 18:04

1 answer

Andrew Clark · Accepted Answer · 2012-05-21T19:02:49+0000

JavaScript does not support lookbehinds. Here is one way to achieve the same behavior:

text = text.replace(/(br|p|\/p|b|\/b)?>/g, function($0, $1){
    return $1 ? $0 : "&gt;";
});

This approach comes from the following blog post: Mimicking Lookbehind in JavaScript

Below is the updated fiddle .