How to change string to number and plus 1 with 000 in front of it

How to change string to number and plus 1 with 000 in front of it ( I’m using javascirpt node JS)

ex 
const string = "0009"
const newString =  string + 1

I want outout 0010

this is what I try

const newString = parseInt(string)+1
const ans = '000' + newString

the problem is output is 00010 I want 0010

if more number 0 will less like 0999 or 9999

Answer

Try it

const newString = parseInt(string)+1
const ans = ('0000'+newString).slice(-4);