Develop Reference

How do I pass a variable into regex with Node js?

So basically, I have a regular expression which is
var regex1 = /10661\" class=\"fauxBlockLink-linkRow u-concealed\">([\s\S]*?)<\/a>/;
var result=text.match(regex1);
user_activity = result[1].replace(/\s/g, "")
console.log(user_activity);
What I'm trying to do is this
var number = 1234;
var regex1 = /${number}\" class=\"fauxBlockLink-linkRow u-concealed\">([\s\S]*?)<\/a>/;
but it is not working, and when I tried with RegExp, I kept getting errors.

You can use RegExp to create regexp from a string and use variables in that string.
var number = 1234;
var regex1 = new RegExp(`${number}aa`);
console.log("1234aa".match(regex1));

You can build the regex string with templates and/or string addition and then pass it to the RegExp constructor. One key in doing that is to get the escaping correct as you need an extra level of escaping for backslashes because the interpretation of the string takes one level of backslash, but you need one to survive as it gets to the RegExp contructor. Here's a working example:
function match(number, str) {
let r = new RegExp(`${number}" class="fauxBlockLink-linkRow u-concealed">([\\s\\S]*?)<\\/a>`);
return str.match(r);
}
const exampleHTML = 'Some link text';
console.log(match(1234, exampleHTML));
Note, using regex to match HTML like this becomes very order-sensitive (whereas the HTML itself isn't order-sensitive). And, your regex requires exactly one space between classes which HTML doesn't. If the class names were in a slightly different order or spacing different in the <a> tag, then it would not match. Depending upon what you're really trying to do, there may be better ways to parse and use the HTML that isn't order-sensitive.

I solved it with the method of Adem,
function escapeRegExp(string) {
return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // $& means the whole matched string
}
var number = 1234;
var firstPart = `<a href="/forum/search/member?user_id=${number}" class="fauxBlockLink-linkRow u-concealed">`
var regexpString = escapeRegExp(firstPart) + '([\\s\\S]*?)' + escapeRegExp('</a>');
console.log(regexpString)
var sample = ` `
var regex1 = new RegExp(regexpString);
console.log(sample.match(regex1));
in the first place the issue was actually the way I was reading the file, the data I was applying the match on, was undefined.

Javascript RegEx contains

I'm using Javascript RegEx to compare if a string matches a standart format.
I have this variable called inputName, which has the following format (sample):
input[name='data[product][tool_team]']
And what I want to achieve with Javascript's regex is to determine if the string has the following but contains _team in between those brackets.
I tried the following:
var inputName = "input[name='data[product][tool_team]']";
var teamPattern = /\input[name='data[product][[_team]]']/g;
var matches = inputName.match(teamPattern);
console.log(matches);
I just get null with the result I gave as an example.
To be honest, RegEx isn't really my area, so I suppose it's wrong.

A couple of things:
You need to escape [ and ] as they have special meaning in regex
You need .* (or perhaps [^[]*) in front of _team if you want to allow anything there ([^[]* means "anything but a [ repeated zero or more times)
Example if you just want to know if it matches:
var string = "input[name='data[product][tool_team]']";
var teamPattern = /input\[name='data\[product\]\[[^[]*_team\]'\]/;
console.log(teamPattern.test(string));
Example if you need to capture the xyz_team bit:
var string = "input[name='data[product][tool_team]']";
var teamPattern = /input\[name='data\[product\]\[([^[]*_team)\]'\]/;
var match = string.match(teamPattern);
console.log(match ? match[1] : "no match");

If you are trying to check for DOM elements you can use attribute contains or attribute equals selector
document.querySelectorAll("input[name*='[_team]']")

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 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.

Regular expression in Javascript (without jQuery)?

I am new to Javascript and recently I wanted to use regular expression in order to get a number from url and store it into a var as string and another var as digit. For example I want to get the number 55 from the below webpage (which is not an accrual page) and I want to store it in a var.
I tried this but it is not working
https://www.google.com/55.html
url.replace(/(\d+)(\.html)$/, function(str, p1, p2) {
return((Number(p1) + 1) + p2);
Please I need help but not with jQuery because it does not make a lot of sense to me.

var numPortion = url.match(/(\d+)\.html/)[1]
(Assumes a match; if it might not match, check the results before applying the array subscript.)

Try this
var a="https://www.google.com/55.html";
var match = a.match(/(\d+)(\.html)/);
match is an array,
match[0] contains the matched expression from your script,
match[1] is the number (the 1st parenthesis),
and so on

var url = 'http://www.google.com/55.html';
var yournumber = /(\d+)(\.html)$/.exec(url);
yournumber = yournumber && yournumber[1]; // <-- shortcut for using if else