I agree that no setter (I didn't see one in the spec) is not Web compatible. In fact, I recall Bluebird running into serious issues with erroneous warnings over read-only stacks in PhantomJS, and had to disable them in my tests as a result. (I eventually dropped the dependency in favor of native promises + a smaller polyfill, but not until later.)
But I do have a couple questions: 1. What does Firefox do with the getter on non-errors? Does it delegate to the own `stack`? (I'm not familiar) 2. How breaking is having the getter and setter throwing on non-errors? I'm struggling to see how it'd be that breaking. It's a getter, not a method, so it requires a call to `__locateGetter__` or `Object.defineProperty` to even access. Also, V8 returns a lazily computed value descriptor (spec violation, unlikely to be fixed before this is implemented). On Thu, Jan 19, 2017, 09:21 Boris Zbarsky <[email protected]> wrote: > On 1/19/17 2:33 AM, Jordan Harband wrote: > > The beginnings of the Error Stacks proposal is now up > > at https://github.com/ljharb/proposal-error-stacks > > I can't speak for other browsers, but the description of the Firefox > behavior in that proposal does not look correct. > > Here's what I understand the Firefox behavior to be: > > 1) The getter does NOT throw on a non-Error receiver. Doing that > would be very much not web-compatible. > 2) The behavior of the getter is as follows: > > a) If the receiver is not an object, throw. > b) Walk up the prototype chain (note: this can invoke proxy > [[GetPrototype]] traps) until we find either an Error object > or Error.prototype. If we reach null before doing either of > those, throw. > c) Return the stack string for the object we found. For > Error.prototype this would be the empty string; for an Error > object it's the stack captured when it was created. > > 3) The setter doesn't care what the receiver is, as long as it's > an object. Again, throwing for non-Error would not be > web-compatible. > 4) The actual behavior of the setter is to throw if called with > no arguments. Otherwise, the setter invokes its receiver's > [[DefineOwnProperty]] with the property name "stack" and a > property descriptor that looks like this: > > { [[Value]]: setterArg, [[Configurable]]: true, > [[Writable]]: true, [[Enumerable]]: true } > > where setterArg is the first argument that was passed to the > setter. > > I should note, per items 1 and 3 above, that the proposal at > https://ljharb.github.io/proposal-error-stacks/ as of today is in fact > not web-compatible. > > -Boris > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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