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Regex: Replace last segment of url

I try to figure out the correct regex to replace the last segment of an url with a modified version of that very last segment. (I know that there are similar threads out there, but none seemed to help...)
Example:
https://www.test.com/one/two/three/mypost/
--->
one/two/three?id=mypost
https://www.test.com/one/mypost/
--->
one?id=mypost
Now I am stuck here:
https://regex101.com/r/9GqYaU/1
I can get the last segment in capturing group 2 but how would I replace it?
I think I will have to something like this:
const url = 'https://www.test.com/one/two/three/mypost/'
const regex = /(http[s]?:\/\/)([^\/]+\/)*(?=\/$|$)/
const path = url.replace(regex, `${myUrlWithoutTheLastSegmentAnd WithoutHTTPS}?id=$2`)
return path
But I have no idea how to get the url without the last segment. I have currently only access to the whole string or group 1 (which is useless in this case) and then group 2, but not the string without group 2.
I would be very glad for any help here. Sometimes I just lack the knowledge of what is possible with regex and how to achieve it.
Thank you in advance.
Cheers

You could use the URL class to extract the pathname and substring to remove the first '/'.
Then, you could put the last part of the pathname in a group and use it as a reference $1 for the replacement.
const url = new URL('https://www.test.com/one/two/three/mypost/').pathname.substring(1)
console.log(url.replace(/\/([^/]*)\/$/, '?id=$1'))

I came across your question yesterday and agree with going down the route of parsing the URL. Once you get there you could even use JavaScript array methods which I prefer to string methods like:
pathname.split("/").filter(p => p.length).pop()
This would separate each folder, ignore any with no length (i.e. handle a trailing slash) and return the last one (mypost).
Anyway, I am also learning regex so sometimes when I find a question like this I just try to find the answer anyway as the best way of learning is doing. It took 24 hours 😂 I came up with this:
/(https?:\/\/).+?([a-z-]*)\/?$/gm
(https?:\/\/) you know what this does. Small correction, you don't need the square brackets. Question mark matches 0 or 1 of the preceding character. As we're only matching s this just works. If you wanted to match s or z you would use [sz]?. I think.
.+? this is the cool one I think I will use in future now I found it. The question mark here has a different meaning - it makes .+ (which means one or more of any character) non-greedy. That means it stops applying once it reaches the next rule. Which is...
([a-z-]*) any number of letters or a hyphen. You should maybe change this to include numbers and upper case.
\/? Optional slash
$ all this must apply at the end of the string.
Here is a demo
https://regex101.com/r/mQNkIS/1

regex pattern a then b then a, one or more times

I want to use regex to find a repeating pattern but I can't work out how to do it. I want to get all matches where there is a number then a plus symbol then another number, including repeats.
So for example, if the string is "5+2-6+10+3", I want to end up with ["5+2", "6+10+3"]
So far I've got
\d*\+\d*
But that doesn't capture the final "+3" in the example above. I had a few attempts using brackets for capturing groups but I couldn't get the output I wanted.
Any help would be much appreciated!

Solved using the following (thanks The fourth bird):
\d+(?:\+\d+)+

What Regex would capture both the beginning and end from of a string?

I am trying to edit a DateTime string in typescript file.
The string in question is 02T13:18:43.000Z.
I want to trim the first three characters including the letter T from the beginning of a string AND also all 5 characters from the end of the string, that is Z000., including the dot character. Essentialy I want the result to look like this: 13:18:43.
From what I found the following pattern (^(.*?)T) can accomplish only the first part of the trim I require, that leaves the initial result like this: 13:18:43.000Z.
What kind of Regex pattern must I use to include the second part of the trim I have mentioned? I have tried to include the following block in the same pattern (Z000.)$ but of course it failed.
Thanks.
Any help would be appreciated.

There is no need to use regular expression in order to achieve that. You can simply use:
let value = '02T13:18:43.000Z';
let newValue = value.slice(3, -5);
console.log(newValue);
it will return 13:18:43, assumming that your string will always have the same pattern. According to the documentation slice method will substring from beginIndex to endIndex. endIndex is optional.

as I see you only need regex solution so does this pattern work?
(\d{2}:)+\d{2} or simply \d{2}:\d{2}:\d{2}
it searches much times for digit-digit-doubleDot combos and digit-digit-doubleDot at the end
the only disadvange is that it doesn't check whether say there are no minutes>59 and etc.
The main reason why I didn't include checking just because I kept in mind that you get your dates from sources where data that are stored are already valid, ex. database.

Solution
This should suffice to remove both the prefix from beginning to T and postfix from . to end:
/^.*T|\..*$/g
console.log(new Date().toISOString().replace(/^.*T|\..*$/g, ''))
See the visualization on debuggex
Explanation
The section ^.*T removes all characters up to and including the last encountered T in the string.
The section \..*$ removes all characters from the first encountered . to the end of the string.
The | in between coupled with the global g flag allows the regular expression to match both sections in the string, allowing .replace(..., '') to trim both simultaneously.

Regex expression for exactly known pattern without "cutting into" the string not working

I am currently developing a web-application where I work with java, javascript, html, jquery, etc. and at some point I need to check that whether an input matches a known pattern and only proceed if it is true.
The pattern should be [at least one but max 3 numbers between 0-9]/[exactly 4 numbers between 0-9], so the only acceptable variations should be like
1/2014 or 23/2015 or 123/2016.
and nothing else, and I CANNOT accept something like 1234/3012 or anything else, and this is my problem right here, it accepts everything in which it can find the above pattern, so like from 12345/6789 it accepts and saves 345/6789.
I am a total newbie with regex, so I checked out http://regexr.com and this is the code I have in my javascript:
$.validator.addMethod("hatarozat", function(value, element) {
return (this.optional(element) || /[0-9]{1,3}(?:\/)[0-9]{4}/i.test(value));
}, "Hibás határozat szám!");
So this is my regex: /[0-9]{1,3}(?:\/)[0-9]{4}/i
which I built up using the above website. What could be the problem, or how can I achived what I described? I tried /^[0-9]{1,3}(?:\/)[0-9]{4}$/ibut this doesn't seem to work, please anyone help me, I have everything else done and am getting pretty stressed over something looking so simple yet I cannot solve it. Thank you!

Your last regex with the anchors (^ and $) is a correct regex. What prevents your code from working is this.optional(element) ||. Since this is a static thing, and is probably true, so it does not show any error (as || is an OR condition, if the first is true, the whole returns true, the regex is not checked at all).
So, use
return /^[0-9]{1,3}\/[0-9]{4}$/.test(value);
Note you do not need the (?:...) with \/ as the grouping does not do anything important here and is just redundant. The anchors are important, since you want the whole string to match the pattern (and ^ anchors the regex at the start of the string and $ does that at the end of the string.)

You need use the the following special characters in your regex expression:
^ and $
or \b
so 2 regexp will be correct:
/\b[0-9]{1,3}(?:\/)[0-9]{4}\b/i;
or
/^[0-9]{1,3}(?:\/)[0-9]{4}$/i

RegEx for subdomain with varying number

Using Javascript RegExp, I'm trying to match URL like the following:
http://sub.domain.com/
http://sub1.domain.com/
http://sub100.domain.com/
I tried the following regex, which isn't working - not sure what I'm doing wrong ?
^http\:\/\/sub\d*\.domain\.com\/$
EDIT: fixed copy & paste typo
Update: For some reason, document.location.href doesn't match the regex - even though examples below (also on regex101.com) do work as expected. My workaround for now - I just match any subdomain.
..any help is much appreciated!

i dont understand How you can compare a grape with a mango
here is the corrected regex :
/^http\:\/\/subs\d*\.app\.clicktale\.com\/$/.test("http://subs14.app.clicktale.com/");
run this command in your console, right now.
you will get true , if you use search then you will get 0 because the index of your match is 0

Well the sub-domains you showed have the token "sub", but your REGEX is looking for "subs".
Also, no need to escape colons.
You don't say whether you wish to test for a match or actually capture the sub-domain. I'll assume the latter:
var match = "http://foo.bar.com".match(/https?:\/\/(([^.]+)\.)?/);
alert(match[2]); //"foo"