2011/6/20 Tom Van Cutsem <[email protected]> > The updated strawman is already more akin to your proposed second > implementation. The way I currently think about a Proxy's > [[DefineOwnProperty]] method with support for fixed properties is as > follows: > > [[DefineOwnProperty]] (P, Desc, Throw) > 1. Let handler be the value of the [[Handler]] internal property of O. > 2. Let defineProperty be the result of calling the [[Get]] internal method > of handler with argument “defineProperty”. > 3. If defineProperty is undefined, throw a TypeError exception. > 4. If IsCallable(defineProperty) is false, throw a TypeError exception. > 5. Let trapResult be the result of calling the [[Call]] internal method of > defineProperty providing handler as the this value, P as the first argument > and Desc as the second argument. > 6. If ToBoolean(trapResult) is false, reject. > 7. Let desc be ToPropertyDescriptor(trapResult) > 8. If [[GetOwnProperty]](P) is not undefined, or desc.[[Configurable]] is > false > a. return [[DefineOwnProperty]](P, desc, Throw) (as per ES5 8.12.9) > 9. return true >
Bugfix: we can't just let the handler reject if P already denotes a fixed property: [[DefineOwnProperty]] (P, Desc, Throw) 1. Let handler be the value of the [[Handler]] internal property of O. 2. Let defineProperty be the result of calling the [[Get]] internal method of handler with argument “defineProperty”. 3. If defineProperty is undefined, throw a TypeError exception. 4. If IsCallable(defineProperty) is false, throw a TypeError exception. 5. Let trapResult be the result of calling the [[Call]] internal method of defineProperty providing handler as the this value, P as the first argument and Desc as the second argument. 6. Let fixedProperty be the result of calling Object.[[GetOwnProperty]](P) 7. If ToBoolean(trapResult) is false, a. If fixedProperty is undefined, reject. b. Otherwise, fixedProperty is defined, so throw a TypeError. 8. Let desc be ToPropertyDescriptor(trapResult) 9. If fixedProperty is not undefined, or desc.[[Configurable]] is false a. Return Object.[[DefineOwnProperty]](P, desc, Throw) 10. Return true Clarification: Object.[[GetOwnProperty]] and Object.[[DefineOwnProperty]] refer to the algorithms for Object values from ES5 sections 8.12.1 and 8.12.9 respectively. They are used to manipulate a proxy's set of fixed properties, which are all non-configurable (since the only way they end up in that record is by virtue of the second condition in line 9)
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