Object.defineProperties must not throw when provided undefined in place of a descriptor

[claudepache]

Apparently, a change between ES5 and ES6 not reflected in the test suite, (neither in the few implementations I have checked, BTW).

test/built-ins/Object/defineProperties/15.2.3.7-5-b-1.js contains:

var obj = {};
assert.throws(TypeError, function() {
            Object.defineProperties(obj, {
                prop: undefined
            });
});

(I have not checked the numerous other tests about the same step.)

However, according to ecma262#sec-objectdefineproperties Step 5.b, undefined values must not throw, but be ignored.

[leobalter]

It properly throws a TypeError when you call ToPropertyDescriptor passing an undefined value:

6.2.4.5 ToPropertyDescriptor ( Obj )

1. If Type(Obj) is not Object, throw a TypeError exception.
...

---

19.1.2.3.1 Runtime Semantics: ObjectDefineProperties ( O, Properties )

1. If Type(O) is not Object, throw a TypeError exception.
2. Let props be ? ToObject(Properties).
3. Let keys be ? props.[[OwnPropertyKeys]]().
4. Let descriptors be a new empty List.
5. Repeat for each element nextKey of keys in List order,
  a. Let propDesc be ? props.[[GetOwnProperty]](nextKey).
  b. If propDesc is not undefined and propDesc.[[Enumerable]] is true, then
    i. Let descObj be ? Get(props, nextKey).
    ii. Let desc be ? ToPropertyDescriptor(descObj).
...
---

var o = {};
var properties = { prop: undefined };

Object.defineProperties(o, properties);
// props = properties
// keys = [ 'prop' ]
// keys => each( nextKey ):
//   nextKey = 'prop'
//   propDesc = props.[[GetOwnProperty]]('prop')
//   propDesc = {value: undefined, writable: true, enumerable: true, configurable: true}
//   descObj = Get(props, 'prop')
//   descObj = undefined
//   desc = ToPropertyDescriptor(undefined)
//     => descObj((undefined)) is not Object, throw a TypeError exception.

[claudepache]

There was some confusion of my part: In step 5b of DefinePropertyDescriptors, the condition is propDesc is undefined, and not propDesc.[[Value]] is undefined. Sorry.

[leobalter]

It is confusing as it catches the prop descriptors to find the enumerables
properties.

Btw, propDesc.value is undefined, but [[Value]] is the value of propDesc.

On Friday, May 27, 2016, Claude Pache notifications@github.com wrote:

There was some confusion of my part: In step 5b of
DefinePropertyDescriptors, the condition is propDesc is undefined, and
not propDesc.[[Value]] is undefined. Sorry.

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[leobalter]

Or no, I'm in a train and will revise my last comment in a better moment.

On Friday, May 27, 2016, Leo Balter leonardo.balter@gmail.com wrote:

It is confusing as it catches the prop descriptors to find the enumerables
properties.

Btw, propDesc.value is undefined, but [[Value]] is the value of propDesc.

On Friday, May 27, 2016, Claude Pache <notifications@github.com
javascript:_e(%7B%7D,'cvml','notifications@github.com');> wrote:

There was some confusion of my part: In step 5b of
DefinePropertyDescriptors, the condition is propDesc is undefined, and
not propDesc.[[Value]] is undefined. Sorry.

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