[simonkundrik]

new WebSocket(url) changes url.protocol from http: to ws: (and from https: to wss:) on the url.URL object it is given, so code that keeps using the URL afterwards sees a different one:

const url = new URL('http://localhost/foo');
const ws = new WebSocket(url);

console.log(url.href); // 'ws://localhost/foo'

This parses a copy of the URL object instead, as is already done for strings. I added a test, which fails on master. npm test passes and eslint and prettier are clean.