How to insert a bracket between the specified alphabet (i.e. A, D, F, R) and the digit using regular expression?

How to insert a bracket between the specified alphabet (i.e. A, D, F, R) and the digit using regular expression?

input:

A1
F42
D3
R6

Expected output:

(A)1
(F)42
(D)3
(R)6

What I have tried:

let inputString="f42"
let expPattern=/[ADFR]\d{1,3}/ig;
 console.log(inputString.replace(expPattern,"(`$0`)"));

It returns "$0" only.

How can I implement the replacement?

You should enclose the alphabet and the digits in separate capture groups so you can reference them in the replacement string:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let inputString="F42"
let expPattern=/([ADFR])(\d{1,3})/ig;
console.log(inputString.replace(expPattern,"($1)$2"));

<!-- end snippet -->

If you want to use the full match in the replacement, you can make use of a positive lookahead (?=\d{1,3}\b) asserting 1-3 digits to the right.

To prevent partial matches, you can use word boundaries \b

In the replacement use the full match denoted as $&

See a regex demo with all the replacements.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let inputString="F42"
let expPattern=/\b[ADFR](?=\d{1,3}\b)/ig;
console.log(inputString.replace(expPattern,"($&)"));

<!-- end snippet -->