Proposal Records (a new one)

💡 Ideas
17

You're correct that an explicit access-own syntax like foo:bar could solve part of the problem. As part of my design process I considered a solution like that at some length, so I'm happy to discuss the details of it!

To have parity with what this proposal suggests, that foo:bar would also need to forbid getter invocation. If you did that you'd at least have the security-hole side fairly well covered.

What a new record accessor syntax wouldn't do is create a clear notion of deep equality. This proposal at least makes it clear how you would implement recordsDeepEqual so that it could be implemented in library-space. A proper composites proposal could still follow on, creating a mechanism by which Map and Set could trigger structural equality behavior instead of reference equality behavior.

As for where it makes a big difference, in a word, validation.

let validNodes = new WeakMap();

let nodeFactory = (childNodes) => {
  if (!Object.isDeepRecord(childNodes)) throw new Error();
  for (let i = 0; i < childNodes.length; i++) {
    if (!validNodes.has(childNodes[i])) throw new Error();
  }

  let node = Object.freezeRecord({ childNodes });

  // We can only cache validity for deep immutable structures
  validNodes.add(node);

  return node;
};

Finally I don't contribute to TC39 just out of the goodness of my heart. I'm giving so much time to honing this proposal because I need it urgently. With a new syntax I'd have to either wait years or change every foo.bar to recordGetAt(foo, 'bar'). Neither of those options is attractive to me.