Allen rightly has pointed out several times on es-discuss that WeakMaps
require GC special handling and are costly, compared to private symbols.
This is true not only for GC time, but especially for get/set runtime.
Properties named by Symbols, when implemented, should have the same
polymorphic-inline-caching-or-better fast paths as string-key properties.
/be
Brandon Benvie wrote:
At the very least, WeakMaps are potentially usable today (depending on
the target audience) while symbols are nowhere in sight. I’ve gotten a
lot of mileage out of this function, which as you said provides a
similar effective result as symbols (they differ in that the WeakMap
version isn’t inherited):
function createStorage(creator){
var store = new WeakMap;
creator || (creator = Object.create.bind(null, null, {}));
return function(obj){
var priv = store.get(obj);
if (!priv) store.set(obj, priv = creator(obj));
return o;
};
}
// usage
var _ = createStorage();
function Ctor(val){
_(this).private = val;
}
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