Nathan Wall wrote:
// ES6 Symbols
// Forgive me for not knowing what the current
// correct syntax is for creating a symbol:
let timestamp = new Symbol();
class SimpleDate {
construct(time) {
this.setTime(time);
}
setTime(time) {
this[timestamp] = +time;
}
getTime() {
return this[timestamp];
}
}
// ES6 WeakMap
let timeMap = new WeakMap(),
// Store WeakMap methods to maintain integrity of the internal state.
WeakMapGet = Function.prototype.call.bind(WeakMap.prototype.get),
WeakMapSet = Function.prototype.call.bind(WeakMap.prototype.set);
class SimpleDate {
construct(time) {
this.setTime(time);
}
setTime(time) {
WeakMapSet(timeMap, this, +time);
}
getTime() {
return WeakMapGet(timeMap, this);
}
}
AFAIK the two ES6 implementations above should function the same, except when
(1) a Proxy uses a SimpleDate as the target and (2) a SimpleDate is frozen.
In the case of (1), the implementation using a private symbol will have
internal accesses to the `timestamp` symbol exposed through the
unknownPrivateSymbol trap.
In the case of (2), the implementation using a private symbol will fail on a
call to `setTime` when the object is frozen (I think).
IIRC, private symbols are exempt from freezing.
Herby
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