How to remove all spaces from a string

Short answer

\s in a regular expression means any whitespace character: a space, a tab, a line break:

console.log(' 1 234\t567\n'.replace(/\s/g, ''));

Output:

If only ordinary spaces should go, replaceAll() is enough:

console.log('+1 555 123 4567'.replaceAll(' ', ''));

Output:

+15551234567

To keep single spaces between words, replace a group of spaces with one:

console.log('too    many     spaces'.replace(/\s+/g, ' '));

Output:

too many spaces

trim() removes spaces only at the edges, not inside the string:

console.log('[' + '  a  b  '.trim() + ']');

Output:

[a  b]

String.prototype.replaceAll — Replaces all occurrences of a substring with another string.
String.prototype.replace — Replaces the first match (or all of them with a regex g flag).
String.prototype.trim — Removes whitespace from both ends of a string.