On Tue, May 29, 2012 at 10:21 AM, Brendan Eich <[email protected]> wrote: > Tab Atkins Jr. wrote: >> Make monocle-mustache solely use the "obj.{foo=bar}" >> syntax, so that the other one is a syntax error. There's no good >> reason to give devs the other type of functionality besides >> completeness, and using it will almost always be a mistake on the >> dev's part, I think. > > Who says obj is an Object instance delegating only to Object.prototype? > > >> Is the "setter on Object.prototype" the only observable difference >> between the two? > > Not for mustache, where obj can be any object, with a deep prototype chain, > setters declared via ES5-standard syntax (no definePropert{y,ies}), or > created by an OOP library. > > As Allen points out, classes will (let's hope) allow easy declaration of > deep chains too. > > Beware scenario-solving in an all-or-nothing way. There's no absolute good > here, and while people may (due to Prototype's Object.extend) want = not : > in most cases, that doesn't mean : is unnecessary.
I'm not making the assumption that "obj" in the examples is necessarily an Object with Object.prototype. It's irrelevant to the two points I'm trying to make: 1. The use-case for mustache is to replace current code that does a lot of property-assigning statements with a more concise expression. 2. Devs will generally be surprised by [[DefineOwnProperty]] behavior, since it's not observably different from [[Put]] in current code except in some degenerate cases that aren't seen in non-adversarial scenarios. I would also assert that there's not a strong use-case for giving [[DefineOwnProperty]] substantially more concise syntax. (I'd agree with a somewhat terser API than the current Object.defineProperties(), but I don't think it needs actual syntax support.) When you do have a deep prototype chain, with details possibly buried deep in code that you don't want to look at, how often do you actually want to completely replace a given property? How often is that a good behavior that won't cause accidental bugs due to setters not being called? We switched to [[DefineOwnProperty]] for literals to avoid a specific attack scenario that is extremely unlikely to have an effect on real code, because authors don't normally adjust Object.prototype and thus don't expect anything weird to happen when they create literals. This assumption might change with classes. > Another alternative: give up on mustache since it bends object literal > syntax past its breaking point. > > If we just standardized some flavor of Object.extend (for-in based? own or > in test for properties to copy? no private names? etc.) would developers be > better off? I think we need a chainable expression form of property assigning. How the syntax looks isn't overly important, as long as it's chainable and an expression. ^_^ The "chainable" part, though, probably means that we do need actual syntax for it, rather than adding a new function. ~TJ _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
