How to use if condition in Javascript RegEx?

Question

I am trying to add some rules to Imagus Firefox Extension. I want to capture image parameter from Google Image Search and if it contains the string th_ remove it and redirect. Otherwise just redirect.

This is my RegEx:

/^(?:(?:images|encrypted)\.)?google\.[^/]+/(?:imgres\?(?:[^&]+&)*?imgurl=)(.*)(?:th_)(.*)&imgrefurl=.*/gm

It works fine for URL's which contain string th_ but for other links it breaks.

Here's the link to my work https://regexr.com/3omf5 Have a look and help.

PS: Please note there are two links in the example.

Try with optional quantifier(?). It checks for 0 or 1 occurrence. (?:th_)? — Kavindra
– Kavindra, Commented Apr 24, 2018 at 13:15
Can you please provide a simplified example with input and result? — Chrᴉz remembers Monica
– Chrᴉz remembers Monica, Commented Apr 24, 2018 at 13:40
@zᴉɹɥƆ I've attached a simplified example to the question. — Jeeva Raam
– Jeeva Raam, Commented Apr 24, 2018 at 14:01

Jeeva Raam · Accepted Answer · 2018-04-28 15:14:53Z

2

I found the answer after a fight. And the regex works fine in the Extension.

Ans:

^(?:(?:images|encrypted)\.)?google\.[^/]+/(?:imgres\?(?:[^&]+&)*?imgurl=)(.*)(%2Fimages(?:[\d]{1,9})?%2F)(th_)?(.*)&imgrefurl=.*

Here is th link with answer:
https://regexr.com/3omfh

edited Apr 28, 2018 at 15:14

answered Apr 24, 2018 at 14:37

Jeeva Raam

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1 Comment

Chrᴉz remembers Monica Over a year ago

Well, fine, I was still looking :). You can accept your own answer als well. You still need to escape a slash here: ...google\.[^/]+-->\<--/...

Guilherme Lemmi · Accepted Answer · 2018-04-24 12:57:36Z

0

Add a * after (?:th_), like:

^(?:(?:images|encrypted)\.)?google\.[^/]+/(?:imgres\?(?:[^&]+&)*?imgurl=)(.*)(?:th_)*(.*)&imgrefurl=.*

answered Apr 24, 2018 at 12:57

Guilherme Lemmi

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Jeeva Raam Over a year ago

Then it doesn't remove the th_ from the first link.

Chrᴉz remembers Monica · Accepted Answer · 2018-04-24 13:24:11Z

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^(?:(?:(?:images|encrypted)\.)?google\.[^/]+/(?:imgres\?(?:[^&]+&)*?imgurl=)(.*)(?:th_)(.*)&imgrefurl=.*)|(.+)

Matches your urls with th_ and replaces it or takes the whole url with the additional |(.+) (+ ^(?: ... ) around your regex). You need to replace it with $1$2$3 then

answered Apr 24, 2018 at 13:24

Chrᴉz remembers Monica

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1 Comment

Jeeva Raam Over a year ago

Then it breaks the link2 which doesn't contain 'th_' then I tried using (?) after (?:th_)? then it doesn't remove the 'th_' from the link 1

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