Remove ALL white spaces from text

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,'')

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

.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, "")

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);