URLSearchParams

Build and read query strings with URL and URLSearchParams.

Phase 14 concatenated ?userId= by hand. Prefer URL + URLSearchParams so encoding and multiple keys stay correct. Then pass url.toString() to fetch. 

Built URL appears here.

Build a query string, then GET posts.

Important JavaScript

const url = new URL("https://jsonplaceholder.typicode.com/posts");
url.searchParams.set("userId", String(userId));

const response = await fetch(url.toString());
// Read: url.searchParams.get("userId")