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Replce repeating set of character from end of string using regex

I want to remove all <br> from the end of this string. Currently I am doing this (in javascript) -
const value = "this is an event. <br><br><br><br>"
let description = String(value);
while (description.endsWith('<br>')) {
description = description.replace(/<br>$/, '');
}
But I want to do it without using while loop, by only using some regex with replace. Is there a way?

To identify the end of the string in RegEx, you can use the special $ symbol to denote that.
To identify repeated characters or blocks of text containing certain characters, you can use + symbol.
In your case, the final regex is: (<br>)*$
This will remove 0 or more occurrence of <br> from the end of the line.
Example:
const value = "this is an event. <br><br><br><br>"
let description = String(value);
description.replace(/(<br>)*$/g, '');

You may try:
var value = "this is an event. <br><br><br><br>";
var output = value.replace(/(<.*?>)\1*$/, "");
console.log(output);
Here is the regex logic being used:
(<.*?>) match AND capture any HTML tag
\1* then match that same tag zero or more additional times
$ all tags occurring at the end of the string

Javascript regex between string delimiters

I have the following string:
%||1234567890||Joe||% some text winter is coming %||1234567890||Robert||%
PROBLEM: I am trying to match all occurrences between %||....||% and process those substring matches
MY REGEX: /%([\s\S]*?)(?=%)/g
MY CODE
var a = "%||1234567890||Joe||% some text winter is coming %||1234567890||Robert||%";
var pattern = /%([\s\S]*?)(?=%)/g;
a.replace( pattern, function replacer(match){
return match.doSomething();
} );
Now the patterns seems to be selecting the everything between the first and last occurrence of %|| .... %||
MY
FIDDLE
WHAT I NEED:
I want to iterate over the matches
%||1234567890||Joe||%
AND
%||1234567890||Robert||%
and do something

You need to use a callback inside a String#replace and modify the pattern to only match what is inside %|| and ||% like this:
var a = "%||1234567890||Joe||% some text winter is coming %||1234567890||Robert||%";
var pattern = /%\|\|([\s\S]*?)\|\|%/g;
a = a.replace( pattern, function (match, group1){
var chunks = group1.split('||');
return "{1}" + chunks.join("-") + "{/1}";
} );
console.log(a);
The /%\|\|([\s\S]*?)\|\|%/g pattern will match:
%\|\| - a %|| substring
([\s\S]*?) - Capturing group 1 matching any 0+ chars as few as possible up to the first...
\|\|% - a ||% substring
/g - multiple times.

Because he tries to take as much as possible, and [\s\S] basically means "anything". So he takes anything.
RegExp parts without escaping, exploded for readability
start tag : %||
first info: ([^|]*) // will stop at the first |
separator : ||
last info : ([^|]*) // will stop at the first |
end tag : ||%
Escaped RegExp:
/%\|\|([^\|]*)\|\|([^\|]*)\|\|%/g

regex to match only quotes that aren't in links

can you tell me how I can in javascript using regex to select quoted text, but not the one that is in the link
so I don't want to select these quotes some text
I want to select only normal quoted text
I used
result = content.replace(/"(.*?)"/g, "<i>$1</i>");
to replace all quoted text with italic, but it replaces also href quotes
Thanks :)

If you need an adhoc regex solution, you may match and capture tags, and only replace " symbols in other contexts. Defining a tag as <+non-<s up to the first >, we may use
var s = '"replace this" but <div id="not-here"> "and here"</div>';
var re = /(<[^<]*?>)|"(.*?)"/g;
var result = s.replace(re, function (m,g1,g2) {
return g1? g1 : '<i>' + g2 + '</i>';
});
console.log(result);
The (<[^<]*?>)|"(.*?)" matches:
(<[^<]*?>) - Group 1 (g1 later in the callback) that captures <, 0+ symbols other than < as few as possible up to the first >
| - or
"(.*?)" - ", 0+ chars other than a newline as few as possible captured into Group 2 (g2 later) and a ".
In the callback method, Group 1 is checked for a match, and if yes, we just put the tag back into the result, else, replace with the tags.

The simplest answer would be to use:
/[^=]"(.*)"/
instead of
/"(.*?)"/
But that will also include quotes that have = sign before them.

Why not only work on the actual text of the element... Like:
var anchors = [],
idx;
anchors = Array.prototype.slice.call(document.getElementsByTagName("a"));
for(idx=0; idx<anchors.length; idx++) {
anchors[idx].innerHTML = anchors[idx].innerHTML.replace(/"([^"]*)"/g, '<i>$1</i>');
}
some text that contains a "quoted" part.
<br/>
more "text" that contains a "quoted" part.
Here we get all anchor elements as an array and replace the innerHTML text with a italicized version of itself.

This pattern could be what you're looking for: <.+>.*(\".+\").*</.+>
Used in JavaScript, the following matches "text":
new RegExp('<.+>.*(\".+\").*</.+>', 'g').exec('some "text"')[1]

How to repeat last block in this regex

The following code
var input = "http://local.app.com/frontend/v12/#/M1WPD/!/abcde/!/fghij/";
var regex = new RegExp("(?:.+?#/([a-zA-Z0-9]{5})/(?:!/([a-zA-Z0-9]{5})/)*)");
var result = input.match(regex);
console.log(result);
// ["http://local.app.com/frontend/v12/#/M1WPD/!/abcde/!/fghij/", "M1WPD", "fghij"]
should print this...
["http://local.app.com/frontend/v12/#/M1WPD/!/abcde/!/fghij/", "M1WPD", "abcde", "fghij"]
beside...
["http://local.app.com/frontend/v12/#/M1WPD/!/abcde/!/fghij/", "M1WPD", "fghij"]
What am I doing wrong?

You cannot capture n number of groups through quantifiers..The result is that it would capture the last occurring match in that particular group!
You have to manually select the groups...
It should be:
(?:.+?#/([a-zA-Z0-9]{5})/!/([a-zA-Z0-9]{5})/!/([a-zA-Z0-9]{5})
If there are arbitrary number of matches you can split with the below regex
/[#!]/|/$
The above regex means split the string where there is an occurrence of / followed by # or ! followed by /
OR
/ followed by end of the string $

Regex pattern = new Regex("[^0-9a-zA-Z]*\\w{5,}");
Make the changes as the above code and try

Javascript (node) regex doesn't seem to match start of string

im struggling with regular expressions in Javascript, they don't seem to start at the beginning of the string. In a simple example bellow I want to get the file name and then everything after the first colon
//string
file.text:16: lots of random text here with goes on for ages
//regex
(.?)[:](.*)
// group 1 returns 't'

/^([^:]+):(.*)/.exec('file.text:16: lots of random text here with goes on for ages')
gives ....
["file.text:16: lots of random text here with goes on for ages", "file.text", "16: lots of random text here with goes on for ages"]

Try this regex:
/^([^:]+)[:](.*)/
Explaination:
^ #Start of string
( #Start of capturing class #1
[^:] #Any character other than :
+ #One or more of the previous character class
) #End of capturing class #1
[:] #One :
(.*) #Any number of characters other than newline
The ? operator captures zero or one of the previous symbol only.
You could also use string operations instead:
str = "file.text:16:";
var n = str.indexOf(":");
var fileName = str.substr(0, n);
var everythingElse = str.substr(n);

The ? operator returns 0 or 1 matches. You want the * operator, and you should select everything that isn't a : in the first set
([^:]*)[:](.*)

Non-regexy answer:
var a = s.split(":");
Then join a[1] and remaining elements.
Or just get the index of the first semicolon and create two strings using that.