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Javascript regex to find a string and extract it from whole string

I have a Javascript array of string that contains urls like:
http://www.example.com.tr/?first=DSPN47ZTE1BGMR&second=NECEFT8RYD
http://www.example.com.tr/?first=RTR22414242144&second=YUUSADASFF
http://www.example.com.tr/?first=KOSDFASEWQESAS&second=VERERQWWFA
http://www.example.com.tr/?first=POLUJYUSD41234&second=13F241DASD
http://www.example.com.tr/?first=54SADFD14242RD&second=TYY42412DD
I want to extract "first" query parameter values from these url.
I mean i need values DSPN47ZTE1BGMR, RTR22414242144, KOSDFASEWQESAS, POLUJYUSD41234, 54SADFD14242RD
Because i am not good using regex, i couldnt find a way to extract these values from the array. Any help will be appreciated

Instead of using regex, why not just create a URL object out of the string and extract the parameters natively?
let url = new URL("http://www.example.com.tr/?first=54SADFD14242RD&second=TYY42412DD");
console.log(url.searchParams.get("first")); // -> "54SADFD14242RD"
If you don't know the name of the first parameter, you can still manually search the query string using the URL constructor.
let url = new URL("http://www.example.com.tr/?first=54SADFD14242RD&second=TYY42412DD");
console.log(url.search.match(/\?([^&$]+)/)[1]); // -> "54SADFD14242RD"
The index of the search represents the parameter's position (with index zero being the whole matched string). Note that .match returns null for no matches, so the code above would throw an error if there's no parameters in the URL.

Does it have to use regex? Would something like the following work:
var x = 'http://www.example.com.tr/?first=DSPN47ZTE1BGMR&second=NECEFT8RYD';
x.split('?first=')[1].split('&second')[0];

Try this regex:
first=([^&]*)
Capture the contents of Group 1
Click for Demo
Code
Explanation:
first= - matches first=
([^&]*) - matches 0+ occurences of any character that is not a & and stores it in Group 1

You can use
(?<=\?first=)[^&]+?
(?<=\?first=) - positive look behind to match ?first=
[^&]+? - Matches any character up to & (lazy mode)
Demo
Without positive look behind you do like this
let str = `http://www.example.com.tr/?first=DSPN47ZTE1BGMR&second=NECEFT8RYD
http://www.example.com.tr/?first=RTR22414242144&second=YUUSADASFF
http://www.example.com.tr/?first=KOSDFASEWQESAS&second=VERERQWWFA
http://www.example.com.tr/?first=POLUJYUSD41234&second=13F241DASD
http://www.example.com.tr/?first=54SADFD14242RD&second=TYY42412DD`
let op = str.match(/\?first=([^&]+)/g).map(e=> e.split('=')[1])
console.log(op)

Javascript - When a string does not Match itself [duplicate]

This question already has answers here:
Is there a RegExp.escape function in JavaScript?
(18 answers)
Closed 3 years ago.
I have this Example 1:
myString = 'cdn.google.com/something.png';
console.log(myString.match(myString));
Everything works just fine, but when it comes to Example 2:
myString = 'cdn.google.com/something.png?231564';
console.log(myString.match(myString));
It returns the value of 'null'. I don't know what happened anymore.. I searched for the keywords 'a string does not Match itself' and found nothing. Can somebody help me? Thank you.

The String#match method would treat the argument as a regex(by parsing if not), where . and ? has special meaning.
. matches any character (except for line terminators)
? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed
So . wouldn't cause any problem since . can be used to match any character except line but ? would since it's using to match zero or one-time occurrence of any character.
For eg: .png?23 => matches .png23 or .pn23
From MDN docs :
If a non-RegExp object obj is passed, it is implicitly converted to a RegExp by using new RegExp(obj).
It's better to use String#indexOf instead which returns the index in the string if found or returns -1 if not found.
console.log(myString.indexOf(myString) > -1);

match in Javascript compares a String against a RegEx. Luckily in your first example it works.
I guess you are looking for a method like localCompare.
Hope this helps!

match() search the string using a regular expression pattern.
So
var s = "My String";
s.match(/Regex Here/);
will try to match s for given regular expression .
In your example:-
myString = 'cdn.google.com/something.png'; // It will be treated as regex
console.log(myString.match(myString));
myString = 'cdn.google.com/something.png?231564'; // It will be treated as regex , result differ because of ?
console.log(myString.match(myString));

You can escape the argument to match, however if you do that you could just use == to compare the strings. This post contains a regex string escape function:
How to escape regular expression in javascript?
RegExp.quote = function(str) {
return (str+'').replace(/[.?*+^$[\]\\(){}|-]/g, "\\$&");
};
It can be used like this:
myString = 'cdn.google.com/something.png?231564';
console.log(myString.match(RegExp.quote
(myString)));
If you want to match any number after the question mark, you could do it like this:
myString = 'cdn.google.com/something.png?';
console.log((myString+"18193819").match(RegExp.quote
(myString) + '\\d+'));

Regular expression matching URL parameters

Given the following two strings
?room=any_characters123&name=John
?room=any_characters123
I want to extract "any_characters123" using regular expression.
I've tried
(?<=room=)(\w)+(?=\&)
but this one fails on the second string (because the matched string must end with "&").
How can I edit my regular expression so that it matches any_characters123 in both strings?

Since javascript won't support lookbehinds, you need to use capturing group.
\?room=(\w+)
Example:
> var s = "?room=any_characters123&name=John"
> var s1 = "?room=any_characters123"
undefined
> var re = /\?room=(\w+)/;
undefined
> console.log(re.exec(s)[1])
any_characters123
undefined
> console.log(re.exec(s1)[1])
any_characters123

If you're using JS, lookbehind is not supported. You can modify the regex as follows:
room=([^&]+)

Try putting * in the end of your expression:
room=(\w+)\&*?
It will test for zero or plus ocurrences of &

This should do the trick:
/room=(\w+)&?/
/*
find "room=" then match any word characters (at least one) until you
possibly hit "&"
*/
Example:
/room=(\w+)&?/.test("?room=any_characters123")
// => true
"?room=any_characters123".match(/room=(\w+)&?/)
// => ["room=any_characters123", "any_characters123"]

Run the string through two regex tests, the one you already have, and then this one:
(?<=room=)(\w){1,}$

How to regex test a string for a pattern while excluding certain characters?

I'm getting nowhere with this...
I need to test a string if it contains %2 and at the same time does not contain /. I can't get it to work using regex. Here is what I have:
var re = new RegExp(/.([^\/]|(%2))*/g);
var s = "somePotentially%2encodedStringwhichMayContain/slashes";
console.log(re.test(s)) // true
Question:
How can I write a regex that checks a string if it contains %2 while not containing any / slashes?

While the link referred to by Sebastian S. is correct, there's an easier way to do this as you only need to check if a single character is not in the string.
/^[^\/]*%2[^\/]*$/
EDIT: Too late... Oh well :P

Try the following:
^(?!.*/).*%2

either use inverse matching as shown here: Regular expression to match a line that doesn't contain a word?
or use indexOf(char) in an if statement. indexOf returns the position of a string or char in a string. If not found, it will return -1:
var s = "test/";
if(s.indexOf("/")!=-1){
//contains "/"
}else {
//doesn't contain "/"
}

one line match in JS regex

What is the JavaScript equivalent of this .NET code?
var b = Regex.IsMatch(txt, pattern);

Here are the useful functions for working with regexes.
exec A RegExp method that executes a search for a match in a string. It returns an array of information.
test A RegExp method that tests for a match in a string. It returns true or false.
match A String method that executes a search for a match in a string. It returns an array of information or null on a mismatch.
search A String method that tests for a match in a string. It returns the index of the match, or -1 if the search fails.
replace A String method that executes a search for a match in a string, and replaces the matched substring with a replacement substring.
split A String method that uses a regular expression or a fixed string to break a string into an array of substrings.
Source: MDC
So to answer your question, as the others have said:
/pattern/.test(txt)
Or, if it is more convenient for your particular use, this is equivalent:
txt.search(/pattern/) !== -1

var b = /pattern/.test(txt);

/pattern/.test(txt);
E.g.:
/foo \w+/.test("foo bar");
It returns true for a match, just like IsMatch.

var regex = new RegExp(pattern);
var b = regex.test(text);
You can also use var b = /pattern/.test(text) but then you can't use a variable for the regex pattern.