Pattern for javascript string replacement

Does the following look like acceptable code to replace some escaped regex characters?

  export function parseString(s: string): string {
    let r : string;
    if ( s[0] === 'r' || s[0] === 'R' ) {
      r = s.substring(1); // no escape
    } else {
      r = s.substring(1, s.length - 1);
      r= r.replace('\\n', '\n');
      r= r.replace('\\r', '\r');
      r= r.replace('\"', '"');
      r= r.replace('\'', '\'');
      r= r.replace('\\a', '\a');
      r= r.replace('\\b', '\b');
      r= r.replace('\\r', '\r');
      r= r.replace('\\t', '\v');
      r= r.replace('\\\\', '\\');
      r= r.replace('\\?', '?');
      r= r.replace('\\`', '\`');
      const reg = /\\x../gi;
      const regReseult = r.matchAll(reg);
      let iter = regReseult.next();
      while (!iter.done) {
        r=r.replace(iter.value[0], escape_hex(iter.value[0]));
        iter = regReseult.next();
      }
    }

    return r;
  }

  function escape_hex( s: string ) : string {
    let ss= s.toLowerCase();
    if ( ss[0]!== '\\' || ss[1]!== 'x') {
      throw new Error('Invalid hexadecimal escape sequence');
    }
    if ( ss.length !== 4) {
      throw new Error('Invalid hexadecimal escape sequence');
    }
    const reg = /[0-9a-f][0-9a-f]/i;
    if ( ss.match(reg) === null ) {
      throw new Error('Invalid hexadecimal escape sequence');
    }
    ss= ss.replace('\\x', '0x');

    return String.fromCharCode(_parseInt(ss));
  }

Or, would a better pattern be to capture the various cases as a single regex such as \\[nr"'abrt\\?`] and then do a substitution based on the capture char? What might be the cleanest way to write the above function?

The goal of the above function is to parse a literal string as defined in BigQuery string-literals, which may accept a string in various forms such as "hello", 'hello', and r'hello\nthere'.