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  • Testcase 15.2.3.6-4-123

Testcase 15.2.3.6-4-123

# Bernd Buschinski (14 years ago)

Hello,

I am having trouble understanding where testcase 15.2.3.6-4-123 should fail according to the ecma262 5.1 Document. I get why it should fails, but not in which step exactly.

I really think I am just getting something wrong so I will write down everything what I think happens. If you spot the error please correct me :)

++The Testcase:

/// Copyright (c) 2012 Ecma International. All rights reserved. /**

  • @path ch15/15.2/15.2.3/15.2.3.6/15.2.3.6-4-123.js
  • @description Object.defineProperty - 'O' is an Array, 'name' is the length property of 'O', the [[Value]] field of 'desc' is absent, test TypeError is thrown when updating the [[Writable]] attribute of the length property from false to true (15.4.5.1 step 3.a.i) */

var arrObj = []; try { //1. call Object.defineProperty(arrObj, "length", { writable: false });

//2. call Object.defineProperty(arrObj, "length", { writable: true });

return false;

} catch (e) { return e instanceof TypeError; }

++The Calls:

//1. Call

Array.[[DefineOwnProperty]]("length", desc{writable: false}, true)

oldLenDesc = [GetOwnProperty] // oldLenDesc = { value: 0, writable: true, enumerable: false, configurable: false }

oldLen = oldLenDesc.[[value]] // oldLen = 0

  1. if P == length // true

3.a. if value of desc is absend //true 3.a.i return default [[DefineOwnProperty]]("length", desc{writable: false}, true) // -> call 8.12.9

//8.12.9 [[DefineOwnProperty]] ("length", desc{writable: false}, true)

  1. current = [GetOwnProperty] // current = { value: 0, writable: true, enumerable: false, configurable: false }

  2. extensible = [[Extensible]] //extensible = true;

      1. if current is undefined and ... (does not apply) //false

  4. if desc is empty //false

  5. if desc is current //false, different in writable

  6. if current.[[configurable]] is false //true 7.a. if desc.[[configurable]] is true ... //false, because not set, defaults to not configurable 7.b. if desc.[[Enumerable]] is true AND desc.[[Enumerable]] != current. [[Enumerable]] //false

  7. If IsGenericDescriptor(Desc) is true, then no further validation is required. //true, jump to step 12+13

Final: put length, { value: 0, writable: false, enumerable: false, configurable: false }

  1. Call Done.

length == { value: 0, writable: false, enumerable: false, configurable: false }

===================

//2. Call

Array.[[DefineOwnProperty]]("length", desc{writable: true}, true)

oldLenDesc = [GetOwnProperty] // oldLenDesc = { value: 0, writable: false, enumerable: false, configurable: false }

oldLen = oldLenDesc.[[value]] // oldLen = 0

  1. if P == length // true

3.a. if value of desc is absend //true 3.a.i return default [[DefineOwnProperty]]("length", desc{writable: true}, true) // -> call 8.12.9

//8.12.9 [[DefineOwnProperty]] ("length", desc{writable: true}, true)

  1. current = [GetOwnProperty] // current = { value: 0, writable: false, enumerable: false, configurable: false }

  2. extensible = [[Extensible]] //extensible = true;

      1. if current is undefined and ... (does not apply) //false

  4. if desc is empty //false

  5. if desc is current //false, different in writable

  6. if current.[[configurable]] is false //true 7.a. if desc.[[configurable]] is true ... //false, because not set, defaults to not configurable 7.b. if desc.[[Enumerable]] is true AND desc.[[Enumerable]] != current. [[Enumerable]] //false

  7. If IsGenericDescriptor(Desc) is true, then no further validation is required. //true, jump to step 12+13

Final: put length, { value: 0, writable: true, enumerable: false, configurable: false } 2. Call Done.

length == { value: 0, writable: true, enumerable: false, configurable: false }

So thats how I see what happens and I can not see where it fails. Please enlighten me :)

# Gavin Barraclough (14 years ago)

You're assuming that the descriptor is a generic descriptor - that isn't the case (accessor descriptors don't have a writable property), see 8.10.2, "IsDataDescriptor". As such, we don't return from step 8 of 8.12.9, and instead reach step 10.a.i.