javascriptregexxregexp

XRegExp no look-behind?

I need to use lookbehind of regex in JavaScript, so found Simulating lookbehind in JavaScript (take 2). Also, I found the author Steven Levithan is the one who developed XRegExp.

I git cloned XRegExp 3.0.0-pre, and tested

some lookbehind logic http://regex101.com/r/xD0xZ5 using XRegExp

var XRegExp = require('xregexp');
console.log(XRegExp.replace('foobar', '(?<=foo)bar', 'test'));

It seems not working;

$ node test
foobar

What do I miss? Thanks.

EDIT: My goal is something like

(?<=foo)[\s\S]+(?=bar)

http://regex101.com/r/sV5gD5

(EDIT2 the link was wrong and modifed)

Answer:

var str = "fooanythingbar";
console.log(str);
console.log(str.replace(/(foo)(?:[\s\S]+(?=bar))/g, '$1test'));

//footestbar

Credit goes to @Trevor Senior Thanks!

Solution

  • It is possible to use non-capturing groups for this, e.g.

    $ node
> 'foobar'.replace(/(foo)(?:bar)/g, '$1test')
'footest'

    In the second parameter of String.replace, the special notation of $1 references the first capturing group, which is (foo) in this case. By using $1test, one can think of $1 as a placeholder for the first matching group. When expanded, this becomes 'footest'.

    For more in depth details on the regular expression, view what it matches here.