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Regex - to extract text before the last a hyphen/dash

Example data expected output
sds-rwewr-dddd-cash0-bbb cash0
rrse-cash1-nonre cash1
loan-snk-cash2-ssdd cash2
garb-cash3-dfgfd cash3
loan-unwan-cash4-something cash4
The common pattern is here, need to extract a few chars before the last hyphen of given string.
var regex1= /.*(?=(?:-[^-]*){1}$)/g ; //output will be "ds-rwewr-dddd-cash0" from "sds-rwewr-dddd-cash0-bbb "
var regex2 = /\w[^-]*$/g ; //output will be "cash0" from "ds-rwewr-dddd-cash0"
var res =regex2.exec(regex1.exec(sds-rwewr-dddd-cash0-bbb)) //output will cash0
Although above nested regex is working as expected but may not be optimize one. So any help will be appreciated for optimized regex

You can use
/\w+(?=-[^-]*$)/
If the part before the last hyphen can contain chars other than word chars, keep using \w[^-]*: /\w[^-]*(?=-[^-]*$)/. If you do not need to check the first char of your match, simply use /[^-]+(?=-[^-]*$)/.
See the regex demo.
Details:
\w+ - one or more word chars
(?=-[^-]*$) - that must be followed with - and then zero or more chars other than - till the end of string.
JavaScript demo
const texts = ['sds-rwewr-dddd-cash0-bbb','rrse-cash1-nonre','loan-snk-cash2-ssdd','garb-cash3-dfgfd','loan-unwan-cash4-something'];
const regex = /\w+(?=-[^-]*$)/;
for (var text of texts) {
console.log(text, '=>', text.match(regex)?.[0]);
}

Regex to extract two numbers with spaces from string

I have problem with simple rexex. I have example strings like:
Something1\sth2\n649 sth\n670 sth x
Sth1\n\something2\n42 036 sth\n42 896 sth y
I want to extract these numbers from strings. So From first example I need two groups: 649 and 670. From second example: 42 036 and 42 896. Then I will remove space.
Currently I have something like this:
\d+ ?\d+
But it is not a good solution.

You can use
\n\d+(?: \d+)?
\n - Match new line
\d+ - Match digit from 0 to 9 one or more time
(?: \d+)? - Match space followed by digit one or more time. ( ? makes it optional )
let strs = ["Something1\sth2\n649 sth\n670 sth x","Sth1\n\something2\n42 036 sth\n42 896 sth y"]
let extractNumbers = str => {
return str.match(/\n\d+(?: \d+)?/g).map(m => m.replace(/\s+/g,''))
}
strs.forEach(str=> console.log(extractNumbers(str)))

If you need to remove the spaces. Then the easiest way for you to do this would be to remove the spaces and then scrape the numbers using 2 different regex.
str.replace(/\s+/, '').match(/\\n(\d+)/g)
First you remove spaces using the \s token with a + quantifier using replace.
Then you capture the numbers using \\n(\d+).
The first part of the regex helps us make sure we are not capturing numbers that are not following a new line, using \ to escape the \ from \n.
The second part (\d+) is the actual match group.

var str1 = "Something1\sth2\n649 sth\n670 sth x";
var str2 = "Sth1\n\something2\n42 036 sth\n42 896 sth y";
var reg = /(?<=\n)(\d+)(?: (\d+))?/g;
var d;
while(d = reg.exec(str1)){
console.log(d[2] ? d[1]+d[2] : d[1]);
}
console.log("****************************");
while(d = reg.exec(str2)){
console.log(d[2] ? d[1]+d[2] : d[1]);
}

Replace -84 in string: "my-name-is-dude-84" with '' by regex?

How to Replace -84 in a string: my-name-is-dude-84 with '' Regex?
I means the last '-' + number
I tried :
string = 'my-name-is-dude-84';
let regex = /[^\-*][1-9]/;
let specialChar = string.replace(regex, '');
then I received is my-name-is-dude-
I expect my string will be: my-name-is-dude

You're close, but this is what you need to do (I guess)
string = 'my-name-is-dude-84';
let regex = /-\d+$/;
let specialChar = string.replace(regex, '');
document.write(specialChar);
Your [^\-*] tries to match all characters but \, - and *. Also [1-9] only matches one digit (between 1 and 9). Use \d (all digits), and add a + to make it match one or more. Also, adding an end of string anchor $ to it makes it only match the hyphen+number at the end of the string.

You can use this regex (.*?)-\d+$
regex demo
JavaScript demo
string = 'my-name-is-99-dude-84';
let regex = /(.*?)-\d+$/;
let specialChar = string.replace(regex, "$1");
document.write(specialChar);

Remove consecutive commas with regex

I use
str.replace(/(^,)|(,$)/g, '')
to remove leading and trailing commas.
How can I extend it so I also remove two consecutive commas?
So ,some text,,more text, should become some text,more text?
One way would be to chain with
str.replace(/(^,)|(,$)/g, '').replace(/,,/g, ',')
but then ,some text,,,,more text, will become some text,,more text instead of some text,more text.

Since you appear to be using the str as a source for an array, you can replace all the .replace calls with:
var str = ",some text,,,,more text,";
var resultArray = str.split(',') // Just split the string.
.filter(function(item){ // Then filter out empty items
return item !== '';
});
console.log(resultArray)
No need to worry about leading, trailing or double comma's.

Remove the leading and trailing commas, and then replace multiple consecutive commas by single comma
str.replace(/^,|,$|(,)+/g, '$1');
,+ will match one or more comma, g-global flag to replace all occurrences of it.
var str = ',some text,,more text,';
str = str.replace(/^,|,$|(,)+/g, '$1');
console.log(str);

You may add an alternative branch and enclose it with a capturing group and then use a replace callback method where you can analyze the match groups and perform the replacement accordingly:
var s = ',some text,,,,more text,';
var res = s.replace(/^,|,$|(,+)/g, function(m,g1) {
return g1 ? ',' : '';
});
console.log(res);
To split with commas and get no empty entries in the resulting array, use a simple
console.log(',some text,,,,more text,'.split(',').filter(Boolean));

You could add a positive lookahead with another comma.
var str = ',some text,,more text,';
str = str.replace(/^,|,$|,(?=,)/g, '')
console.log(str);

What about one replace only like: ",some text,,,,more text,".replace(/(^,)|(,$)|,(?=,)/g, '');
[EDIT]
Note that lookbehinds don't work in javascript. so you can only use a lookahead like so.

Remove ALL white spaces from text

$("#topNav" + $("#breadCrumb2nd").text().replace(" ", "")).addClass("current");
This is a snippet from my code. I want to add a class to an ID after getting another ID's text property. The problem with this, is the ID holding the text I need, contains gaps between the letters.
I would like the white spaces removed. I have tried TRIM()and REPLACE() but this only partially works. The REPLACE() only removes the 1st space.

You have to tell replace() to repeat the regex:
.replace(/ /g,'')
The g character makes it a "global" match, meaning it repeats the search through the entire string. Read about this, and other RegEx modifiers available in JavaScript here.
If you want to match all whitespace, and not just the literal space character, use \s instead:
.replace(/\s/g,'')
You can also use .replaceAll if you're using a sufficiently recent version of JavaScript, but there's not really any reason to for your specific use case, since catching all whitespace requires a regex, and when using a regex with .replaceAll, it must be global, so you just end up with extra typing:
.replaceAll(/\s/g,'')

.replace(/\s+/, "")
Will replace the first whitespace only, this includes spaces, tabs and new lines.
To replace all whitespace in the string you need to use global mode
.replace(/\s/g, "")

Now you can use "replaceAll":
console.log(' a b c d e f g '.replaceAll(' ',''));
will print:
abcdefg
But not working in every possible browser:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replaceAll

Regex for remove white space
\s+
var str = "Visit Microsoft!";
var res = str.replace(/\s+/g, "");
console.log(res);
or
[ ]+
var str = "Visit Microsoft!";
var res = str.replace(/[ ]+/g, "");
console.log(res);
Remove all white space at begin of string
^[ ]+
var str = " Visit Microsoft!";
var res = str.replace(/^[ ]+/g, "");
console.log(res);
remove all white space at end of string
[ ]+$
var str = "Visit Microsoft! ";
var res = str.replace(/[ ]+$/g, "");
console.log(res);
var mystring="fg gg";
console.log(mystring.replaceAll(' ',''))

** 100% working
use replace(/ +/g,'_'):
let text = "I love you"
text = text.replace( / +/g, '_') // replace with underscore ('_')
console.log(text) // I_love_you

Using String.prototype.replace with regex, as mentioned in the other answers, is certainly the best solution.
But, just for fun, you can also remove all whitespaces from a text by using String.prototype.split and String.prototype.join:
const text = ' a b c d e f g ';
const newText = text.split(/\s/).join('');
console.log(newText); // prints abcdefg

I don't understand why we need to use regex here when we can simply use replaceAll
let result = string.replaceAll(' ', '')
result will store string without spaces

let str = 'a big fat hen clock mouse '
console.log(str.split(' ').join(''))
// abigfathenclockmouse

Use string.replace(/\s/g,'')
This will solve the problem.
Happy Coding !!!

simple solution could be : just replace white space ask key value
val = val.replace(' ', '')

Use replace(/\s+/g,''),
for example:
const stripped = ' My String With A Lot Whitespace '.replace(/\s+/g, '')// 'MyStringWithALotWhitespace'

Well, we can also use that [^A-Za-z] with g flag for removing all the spaces in text. Where negated or complemente or ^. Show to the every character or range of character which is inside the brackets. And the about g is indicating that we search globally.
let str = "D S# D2m4a r k 23";
// We are only allowed the character in that range A-Za-z
str = str.replace(/[^A-Za-z]/g,""); // output:- DSDmark
console.log(str)
javascript - Remove ALL white spaces from text - Stack Overflow

Using .replace(/\s+/g,'') works fine;
Example:
this.slug = removeAccent(this.slug).replace(/\s+/g,'');

function RemoveAllSpaces(ToRemove)
{
let str = new String(ToRemove);
while(str.includes(" "))
{
str = str.replace(" ", "");
}
return str;
}