Comment by dcode

In more technical jargon, it is about value spaces. All UTF-8 strings map to WTF-16 strings semantically (lists of Unicode Scalar Values are a subset of lists of Unicode Code Points), but some WTF-16 strings do not map to UTF-8 (Unicode Scalar Values exclude some Code Points). That's something UTF-8-based languages have to deal with anyway (on the Web, which is WTF-16, or any other mixed system), but it's odd that the expectation has become that even languages that map to each other incl. to JS/Web APIs now have to share a problem that does not exist in their native VMs for reasons. To emphasize: These languages just do what's perfectly fine in WebIDL, JSON, ECMAScript and their own language specifications.

  let myString = "...";
  let returnedMyString = someFunction(myString); // might or might not cross boundary
  if (myString == returnedMyString) {
    // sometimes silently false
  }

I am having a hard time to understand how so many people prefer this as the outcome of a Web / polyglot / language neutral standard, especially since affected languages cannot change, and the problem is so trivially avoided, say with a boolean flag "this end is WTF-16, it's OK if the other end is as well" (otherwise use well-formed/UTF-8 semantics).

For context, I once gave a presentation about the pitfalls: https://www.youtube.com/watch?v=Ri2NMnSQo4o