JavaScript: equivalent regex as PHP

Question

I have a regular expression to find the next word of given word 'on' in string for php:

(?<=\bon\s)(\w+)

It works perfectly for PHP but for js it gives following error:

Uncaught SyntaxError: Invalid regular expression: /(?<=\bon\s)(\w+)/: Invalid group

What is the equivalent regex for javascript?

@Pakspul - the `/` at the start and end are part of JS's regex literal syntax, not part of the actual pattern. — nnnnnn, Mar 10 '14 at 11:59

Amal Murali · Answer 1 · 2014-03-10T12:24:33.870

2

(?<=\bon\s) is a positive lookbehind. PHP's regular expression engine (PCRE) supports those, but JavaScript's regular expression engine doesn't.

While it's not possible to write an exactly similar regex, you can still achieve this using the following regex:

\bon\s(\w+)

Unlike in the original regex, \bon\s consumes characters. But you can still extract the results using a capturing group (\w+).

Usage:

var str = 'foo on bar';
var matches = str.match(/\bon\s(\w+)/);
var result = matches[1] // bar

edited Mar 10 '14 at 12:24

answered Mar 10 '14 at 11:57

Amal Murali

@GaneshKunwar Huh? I didn't give a solution in this answer. I was explaining why your regex didn't work. – Amal Murali Mar 10 '14 at 12:01

score 1 · Answer 2 · answered Mar 10 '14 at 12:07

1

As Amal Murali explains it, there is no equivalent with Javascript regex. However you can write:

\bon\s(\w+)

and extract the first capturing group.

answered Mar 10 '14 at 12:07

Thanks Casimir for your answer, but it gives two words including 'on'. I need a word after 'on'. – Ganesh Kunwar Mar 10 '14 at 12:14
@GaneshKunwar: this is the reason why you must **extract** the capturing group from the match result. Take a look at this topic: http://stackoverflow.com/questions/432493/how-do-you-access-the-matched-groups-in-a-javascript-regular-expression – Casimir et Hippolyte Mar 10 '14 at 12:15

2 Answers2