For the CSS Variables spec I need to define an object with arbitrary string keys, with the initial set determined by the custom properties set in the style rule, and on modification I need to coerce the provided key to a string, and then go mutate the style rule accordingly. When the style rule is mutated to add/remove custom properties, I also need to mutate the exposed keys on the object. (In other words, this object has a bidirectional link with a style rule; it just exposes a more convenient and specialized interface for custom properties specifically.)
Right now I'm defining this via the WebIDL getter/setter/etc hooks, which ends up defining an "object map". This is bad practice, though, because anything set on the prototype chain will show up as a (non-own) key, potentially causing confusion. I'd like to convert this over to an ES Map, as that avoids the above issue and gets me all the Map extras for free, which is nice. However, I don't think it's currently possible to do what I need. Is it possible add appropriate hooks to the ES spec to let me define the [[MapData]] via a spec, rather than as an initially-empty list of tuples that get/set unconditionally read from? I need to be able to define in spec-ese that the [[MapData]] tuples consist of some list of data from a style rule, and that whenever a value gets set, I first coerce the key to a string, and then go mutate the style rule instead of the [[MapData]] (it then picks up the mutated data by virtue of being defined by the style rule). (One way to do this today is to subclass Map and provide my own get/set/etc. functions, but I need to override a potentially-open set (anything that doesn't directly lean on my overridden functions), and it doesn't prevent people from directly twiddling my [[MapData]] by calling Map.prototype.set.call() on my object.) Alternately: Proxies? Is that possible? What benefits/drawbacks come from that? ~TJ _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
