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regex get part of the link

https://www.example.com/uk/This-Part-I-Need-To-Get/F1ST2/sometext/
need to get "This-Part-I-Need-To-Get", with "-" symbols and capital letters at the wordstart.
All I managed to do is "/([A-Z-])\w+/g", that returns
"This" "-Part" "-I" "-Need" "-To" "-Get" "F1ST2", but I don`t need "F1ST2".
How should I do it?

It might depend on URL format, but at this point:
var url = 'https://www.example.com/uk/This-Part-I-Need-To-Get/F1ST2/sometext/';
console.log(url.split('/')[4])

Try this regex
/([A-Z][a-z]|-[A-Z]|-[A-Z][a-z]-|-[A-Z]-)\w+/g
Here is a SNIPPET
var url = 'https://www.example.com/uk/This-Part-I-Need-To-Get/F1ST2/sometext/';
console.log(url.match(/([A-Z][a-z]|-[A-Z]|-[A-Z][a-z]-|-[A-Z]-)\w+/g).join(''))

As #MichałSałaciński said, you should consider using split function.
BTW, if you wan't to use regular expressions, then this one will work if url format does not change : [^\/]+(?=(?:\/\w+){2}\/)
Demo
var re = /[^\/]+(?=(?:\/\w+){2}\/)/
var url = "https://www.example.com/uk/This-Part-I-Need-To-Get/F1ST2/sometext/"
if(re.test(url)) {
// URL match regex pattern, we can safely get full match
var value = re.exec(url)[0];
console.log(value);
}
Explanation
[^\/]+ Any character but a slash n times
(?=...) Followed by
(?:\/\w+){2}\/ a slash and any word character (2 times) then a slash
Solution 2
This one also works using captured group 1: :\/\/[^\/]+\/[^\/]+\/([^\/]+)
Demo
var re = /:\/\/[^\/]+\/[^\/]+\/([^\/]+)/;
var url = "https://www.example.com/uk/This-Part-I-Need-To-Get/F1ST2/sometext/";
if(re.test(url)) {
// URL match regex pattern, we can safely get group 1 value
var value = re.exec(url)[1];
console.log(value );
}

Removing a letters located between to specific string

I want to make sure that the URL I get from window.location does not already contain a specific fragment identifier already. If it does, I must remove it. So I must search the URL, and find the string that starts with mp- and continues until the end URL or the next # (Just in case the URL contains more than one fragment identifier).
Examples of inputs and outputs:
www.site.com/#mp-1 --> www.site.com/
www.site.com#mp-1 --> www.site.com
www.site.com/#mp-1#pic --> www.site.com/#pic
My code:
(that obviously does not work correctly)
var url = window.location;
if(url.toLowerCase().indexOf("#mp-") >= 0){
var imgString = url.substring(url.indexOf('#mp-') + 4,url.indexOf('#'));
console.log(imgString);
}
Any idea how to do it?

Something like this? This uses a regular expression to filter the unwanted string.
var inputs = [
"www.site.com/#mp-1",
"www.site.com#mp-1",
"www.site.com/#mp-1#pic"
];
inputs = inputs.map(function(input) {
return input.replace(/#mp-1?/, '');
});
console.log(inputs);
Output:
["www.site.com/", "www.site.com", "www.site.com/#pic"]
jsfiddle: https://jsfiddle.net/tghuye75/
The regex I used /#mp-1?/ removes any strings like #mp- or #mp-1. For a string of unknown length until the next hashtag, you can use /#mp-[^#]* which removes #mp-, #mp-1, and #mp-somelongstring.

Use regular expressions:
var url = window.location;
var imgString = url.replace(/(#mp-[^#\s]+)/, "");
It removes from URL hash anything from mp- to the char before #.
Regex101 demo

You can use .replace to replace a regular expression matching ("#mp-" followed by 0 or more non-# characters) with the empty string. If it's possible there are multiple segments you want to remove, just add a g flag to the regex.
url = url.replace(/#mp-[^#]*/, '');

The window.location has the hash property so... window.location.hash
The most primitive way is to declare
var char_start, char_end
and find two "#" or one and the 2nd will be end of input.
with that... you can do what you want, the change of window.location.hash will normally affect the browser adress.
Good luck!

Removing a query string using regex in java script

I have a requirement of removing a query parameter coming with a REST API call. Below are the sample URLs which need to be considered. In each of this URL, we need to remove 'key' parameter and its value.
/test/v1?key=keyval&param1=value1&param2=value2
/test/v1?key=keyval
/test/v1?param1=value1&key=keyval
/test/v1?param1=value1&key=keyval&param2=value2
After removing the key parameter, the final URLs should be as follows.
/test/v1?param1=value1&param2=value2
/test/v1?
/test/v1?param1=value1
/test/v1?param1=value1=&param2=value2
We used below regex expression to match and replace this query string in php. (https://regex101.com/r/pK0dX3/1)
(?<=[?&;])key=.*?($|[&;])
We couldn't use the same regex in java script. Once we use it in java script it gives some syntax errors. Can you please help us to figure out the issue with the same regex ? How can we change this regex to match and remove query parameter as mentioned above?

Obviously lookbehind isn't supported in Javascript hence your regex won't work.
In Javascript you can use this:
repl = input.replace(/(\?)key=[^&]*(?:&|$)|&key=[^&]*/gmi, '$1');
RegEx Demo
Regex is working on 2 paths using regex alternation:
If this query parameter is right after ? then we grab till & after parameter and place ? back in replacement.
If this query parameter is after & then &key=value is replaced by an empty string.

The regex works in PHP but not in Javascript because Javascript does not support lookbehind.
The easiest fix here would be to replace the lookbehind (?<=[?&;]) with the equivalent characters in a capturing group ([?&;]) and use a backreference ($1) to insert this bit back into the replacement string.
For example:
var path = '/test/v1?key=keyval&param1=value1&param2=value2';
var regex = /([?&;])key=.*?($|[&;])/;
console.log(path.replace(regex, '$1'); // outputs '/test/v1?param1=value1&param2=value2'
Not convinced regex would be the most reliable way of removing a query parameter, but that's a different story :-)

Just in case you want to do it without a regex, here is a function that will do the trick:
var removeQueryString = function (str) {
var qm = str.lastIndexOf('?');
var path = str.substr(0, qm + 1);
var querystr = str.substr(qm + 1);
var params = querystr.split('&');
var keyIndex = -1;
for (var i = 0; i < params.length; i++) {
if (params[i].indexOf("key=") === 0) {
keyIndex = i;
break;
}
}
if (keyIndex != -1) {
params.splice(keyIndex, 1);
}
var result = path + params.join('&');
return result;
};

The lookbehind feature isn't available in javascript, so to test the character before the key/value, you must match it. To make the pattern works whatever the position in the query part of the url, you can use an alternation in a non-capturing group, and you capture the question mark:
url = url.replace(/(?:&|(\?))key=[^&#]*(?:(?!\1).)?/, '$1');
Note: the # is excluded from the character class to prevent the fragment part (if any) of the url to be matched with key value.

Regex to detect a string that contains a URL or file extension

I'm trying to create a small script that detects whether the string input is either:
1) a URL (which will hold a filename): 'http://ajax.googleapis.com/html5shiv.js'
2) just a filename: 'html5shiv.js'
So far I've found this but I think it just checks the URL and file extension. Is there an easy way to make it so it uses an 'or' check? I'm not very experienced with RegExp.
var myRegExp = /[^\\]*\.(\w+)$/i;
Thank you in advance.

How bout this regex?
(\.js)$
it checks the end of the line if it has a .js on it.
$ denotes end of line.
tested here.

Basically, to use 'OR' in regex, simply use the 'pipe' delimiter.
(aaa|bbb)
will match
aaa
or
bbb
For regex to match a url, I'd suggest the following:
\w+://[\w\._~:/?#\[\]#!$&'()*+,;=%]*
This is based on the allowed character set for a url.
For the file, what's your definition of a filename?
If you want to search for strings, that match "(at least) one to many non-fullstop characters, followed by a fullstop, followed by (at least) one to many non-fullstop characters", I'd suggest the following regex:
[^\.]+\.[^\.]+
And altogether:
(\w+://[\w\._~:/?#\[\]#!$&'()*+,;=%]*|[^\.]+\.[^\.]+)
Here's an example of working (in javascript): jsfiddle
You can test it out regex online here: http://gskinner.com/RegExr/

If it is for the purpose of flow control you can do the following:
var test = "http://ajax.googleapis.com/html5shiv.js";
// to recognize http & https
var regex = /^https?:\/\/.*/i;
var result = regex.exec(test);
if (result == null){
// no URL found code
} else {
// URL found code
}
For the purpose of capturing the file name you could use:
var test = "http://ajax.googleapis.com/html5shiv.js";
var regex = /(\w+\.\w+)$/i;
var filename = regex.exec(test);

Yes, you can use the alternation operator |. Be careful, though, because its priority is very low. Lower than sequencing. You will need to write things like /(cat)|(dog)/.
It's very hard to understand what you exactly want with so few use/test cases, but
(http://[a-zA-Z0-9\./]+)|([a-zA-Z0-9\.]+)
should give you a starting point.

If it's a URL, strip it down to the last part and treat it the same way as "just a filename".
function isFile(fileOrUrl) {
// This will return everything after the last '/'; if there's
// no forward slash in the string, the unmodified string is used
var filename = fileOrUrl.split('/').pop();
return (/.+\..+/).test(filename);
}

Try this:
var ajx = 'http://ajax.googleapis.com/html5shiv.js';
function isURL(str){
return /((\/\w+)|(^\w+))\.\w{2,}$/.test(str);
}
console.log(isURL(ajx));

Have a look at this (requires no regex at all):
var filename = string.indexOf('/') == -1
? string
: string.split('/').slice(-1)[0];

Here is the program!
<script>
var url="Home/this/example/file.js";
var condition=0;
var result="";
for(var i=url.length; i>0 && condition<2 ;i--)
{
if(url[i]!="/" && url[i]!="."){result= (condition==1)? (url[i]+result):(result);}
else{condition++;}
}
document.write(result);
</script>

Regex: Getting content from URL

I want to get "the-game" using regex from URLs like
http://www.somesite.com.domain.webdev.domain.com/en/the-game/another-one/another-one/another-one/
http://www.somesite.com.domain.webdev.domain.com/en/the-game/another-one/another-one/
http://www.somesite.com.domain.webdev.domain.com/en/the-game/another-one/

What parts of the URL could vary and what parts are constant? The following regex will always match whatever is in the slashes following "/en/" - the-game in your example.
(?<=/en/).*?(?=/)
This one will match the contents of the 2nd set of slashes of any URL containing "webdev", assuming the first set of slashes contains a 2 or 3 character language code.
(?<=.*?webdev.*?/.{2,3}/).*?(?=/)
Hopefully you can tweak these examples to accomplish what you're looking for.

var myregexp = /^(?:[^\/]*\/){4}([^\/]+)/;
var match = myregexp.exec(subject);
if (match != null) {
result = match[1];
} else {
result = "";
}
matches whatever lies between the fourth and fifth slash and stores the result in the variable result.

You probably should use some kind of url parsing library rather than resorting to using regex.
In python:
from urlparse import urlparse
url = urlparse('http://www.somesite.com.domain.webdev.domain.com/en/the-game/another-one/another-one/another-one/')
print url.path
Which would yield:
/en/the-game/another-one/another-one/another-one/
From there, you can do simple things like stripping /en/ from the beginning of the path. Otherwise, you're bound to do something wrong with a regular expression. Don't reinvent the wheel!