Node JS Character of of Range

Question

I have a regular expression that I'd like to store in a variable. The expression works file when used directly in the file reader but when expressed as a constant, I get a range out of order error.

Here is the expression:

 let regex = "/([a-zA-Z0-9\s_\\.\-\(\):])+(.pdf)/i";

 // The file can be read below

 fs.readdirSync('path').filter((fp) => 
           fp.match(/([a-zA-Z0-9\s_\\.\-\(\):])+(.pdf)/i) !== null);

 //The file cannot be read here when using the constant
 
 fs.readdirSync(WATCHED_DIR).filter((fp) => 
          fp.match(regex)/i) !== null)

If I do this i.e. without the quotes, I get a syntax error.

let regex = /([a-zA-Z0-9\s_\\.\-\(\):])+(.pdf)/i;

SyntaxError: Invalid regular expression: /[a-zA-Z0-9\s_\.-():])+(.pdf)/: Unmatched ')'

How can I correctly store the regular expression in a constant?