Incorrect semantics for globals

[jlongster]

These should be true:

{}.constructor === Object
[].constructor === Array

They are true in node, browser, and are true in production cloudflare pages/workers. They are not true in miniflare.

(my use case is trying to use ClojureScript compiled code which is using these)

[mrbbot]

Hey! 👋 Which version of miniflare are you using? This should be fixed in version 2.0.0. 😕

[jlongster]

I was just looking into it and commenting out the line which proxies globals fixes it, and I don't see that code anymore on github! The newer code for working with globals looks more reasonable and if it's released, should fix it! Will try it out. Thanks a lot! I was worried this would be a weird esoteric thing but looks like it's straight-forward and already being addressed :)

[jlongster]

I am using version 0.0.0-8ab7d2e of wrangler (because it has some fixes for watch mode) which includes version 2.0.0-rc.4 of miniflare. Is the code on github released? I'm still seeing this code in runner-vm in 2.0.0-rc.4:

function proxyHasInstance(target, hasInstance, handler) {
  return new Proxy(target, {
    get(target2, property, receiver) {
      if (property === Symbol.hasInstance)
        return hasInstance;
      return Reflect.get(target2, property, receiver);
    },
    ...handler
  });
}
function makeProxiedGlobals(blockCodeGeneration) {
  if (!blockCodeGeneration)
    blockCodeGeneration = void 0;
  return {
    Object: proxyHasInstance(Object, isObject),
    Array: proxyHasInstance(Array, Array.isArray),
    Promise: proxyHasInstance(Promise, import_util.types.isPromise),
    RegExp: proxyHasInstance(RegExp, import_util.types.isRegExp),
    Error: proxyHasInstance(Error, isError(Error)),
    EvalError: proxyHasInstance(EvalError, isError(EvalError)),
    RangeError: proxyHasInstance(RangeError, isError(RangeError)),
    ReferenceError: proxyHasInstance(ReferenceError, isError(ReferenceError)),
    SyntaxError: proxyHasInstance(SyntaxError, isError(SyntaxError)),
    TypeError: proxyHasInstance(TypeError, isError(TypeError)),
    URIError: proxyHasInstance(URIError, isError(URIError)),
    Function: proxyHasInstance(Function, isFunction, blockCodeGeneration && {
      construct() {
        throw new EvalError("Code generation from strings disallowed for this context");
      }
    })
  };
}

[mrbbot]

I've just created the PR to upgrade to 2.0.0 here: cloudflare/workers-sdk#221. The most recently published version of wrangler should be using 2.0.0-rc.5 which disables this proxying stuff by default, but doesn't have the correct cross-realm instanceof behaviour.

[jlongster]

thanks!

doesn't have the correct cross-realm instanceof behaviour

what constitutes a realm here? what real-world use cases would see this problem? I'm assume each module isn't a realm as that would mean object passed across them wouldn't work. where are the realm boundaries?

[mrbbot]

The comment at the start of this file goes into detail on this. 🙂 The realm boundary is between stuff running in Node (runtime APIs: KV, etc) and stuff running in Miniflare's vm sandbox (user code).

[jlongster]

cool, that's what I figured but wanted to make sure that was right. Shouldn't be a problem for my case, and that tradeoff makes sense!