Le 19/01/2013 19:04, Kevin Smith a écrit :
It calls the unknownPrivateSymbol trap. If the trap throws, the
operation fails. In all other cases (no trap or trap which doesn't
throw), it's forwarded.
And can frozen objects be proxy targets, or no?
Yes they can.
More generally, can a proxy effectively override the behavior of a
non-configurable, non-writable property on the target?
var target = Object.create(null, { foo: { writable: false,
configurable: false, value: 1 } });
var proxy = new Proxy(target, {
get(obj, name) { return name === "foo" ? 0 : obj[name]; }
});
console.log(target.foo); // 1
console.log(proxy.foo); // 0
This this allowed?
It is not. At the exit of the get trap, the JS engine checks whether
invariants should be enforced for the given property on the target. In
your case, the runtime sees that the target has a non-configurable
non-writable property called 'foo' with 1 as value. When you try to
return 0, it will throw a TypeError because of invariant violation. You
can read about invariants at
http://wiki.ecmascript.org/doku.php?id=harmony:direct_proxies#invariant_enforcement
David
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