You must have cty.dat downloaded from officially maintained site
Download it here http://www.country-files.com/bigcty/cty.dat
(async () => {
const ad1cCtyImpl = new AD1CCtyImpl();
try {
await ad1cCtyImpl.loadCty("cty.dat"); // Replace with your file path
console.log("Entities:" + ad1cCtyImpl.entities.size);
console.log("Prefixes:" + ad1cCtyImpl.prefixes.size);
console.log(ad1cCtyImpl.lookup("LY1H"));
} catch (error) {
console.error(error);
}
})();