Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Editorial: Object Environment Record improvements #2287

Merged
merged 5 commits into from
Mar 18, 2021
Merged

Editorial: Object Environment Record improvements #2287

Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
f8ecdd0
Editorial: Have NewGlobalEnvironment invoke NewObjectEnvironment (#2287)
jmdyck Mar 18, 2021
12f93fd
Editorial: Set _withEnvironment_ explicitly (#2287)
jmdyck Mar 18, 2021
90d7dbb
Editorial: Add parameter to NewObjectEnvironemt (#2287)
jmdyck Mar 18, 2021
d7be463
Editorial: Introduce fields to specify object Env Rec (#2287)
jmdyck Mar 18, 2021
dae76f8
Editorial: Rename alias `_bindings_` to `_bindingObject_` (#2287)
jmdyck Mar 18, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
97 changes: 69 additions & 28 deletions spec.html
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8563,18 +8563,58 @@ <h1>WithBaseObject ( )</h1>
<emu-clause id="sec-object-environment-records">
<h1>Object Environment Records</h1>
<p>Each <dfn>object Environment Record</dfn> is associated with an object called its <em>binding object</em>. An object Environment Record binds the set of string identifier names that directly correspond to the property names of its binding object. Property keys that are not strings in the form of an |IdentifierName| are not included in the set of bound identifiers. Both own and inherited properties are included in the set regardless of the setting of their [[Enumerable]] attribute. Because properties can be dynamically added and deleted from objects, the set of identifiers bound by an object Environment Record may potentially change as a side-effect of any operation that adds or deletes properties. Any bindings that are created as a result of such a side-effect are considered to be a mutable binding even if the Writable attribute of the corresponding property has the value *false*. Immutable bindings do not exist for object Environment Records.</p>
<p>Object Environment Records created for `with` statements (<emu-xref href="#sec-with-statement"></emu-xref>) can provide their binding object as an implicit *this* value for use in function calls. The capability is controlled by a _withEnvironment_ Boolean value that is associated with each object Environment Record. By default, the value of _withEnvironment_ is *false* for any object Environment Record.</p>
<p>Object Environment Records created for `with` statements (<emu-xref href="#sec-with-statement"></emu-xref>) can provide their binding object as an implicit *this* value for use in function calls. The capability is controlled by a Boolean [[IsWithEnvironment]] field.</p>
<p>Object Environment Records have the additional state fields listed in <emu-xref href="#table-additional-fields-of-object-environment-records"></emu-xref>.</p>
<emu-table id="table-additional-fields-of-object-environment-records" caption="Additional Fields of Object Environment Records">
<table>
<tbody>
<tr>
<th>
Field Name
</th>
<th>
Value
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
[[BindingObject]]
</td>
<td>
Object
</td>
<td>
The binding object of this Environment Record.
</td>
</tr>
<tr>
<td>
[[IsWithEnvironment]]
</td>
<td>
Boolean
</td>
<td>
Indicates whether this Environment Record is created for a `with` statement.
</td>
</tr>
</tbody>
</table>
</emu-table>
<p>The behaviour of the concrete specification methods for object Environment Records is defined by the following algorithms.</p>

<emu-clause id="sec-object-environment-records-hasbinding-n">
<h1>HasBinding ( _N_ )</h1>
<p>The HasBinding concrete method of an object Environment Record _envRec_ takes argument _N_ (a String). It determines if its associated binding object has a property whose name is the value of the argument _N_. It performs the following steps when called:</p>
<emu-alg>
1. Let _bindings_ be the binding object for _envRec_.
1. Let _foundBinding_ be ? HasProperty(_bindings_, _N_).
1. Let _bindingObject_ be _envRec_.[[BindingObject]].
1. Let _foundBinding_ be ? HasProperty(_bindingObject_, _N_).
1. If _foundBinding_ is *false*, return *false*.
1. If the _withEnvironment_ flag of _envRec_ is *false*, return *true*.
1. Let _unscopables_ be ? Get(_bindings_, @@unscopables).
1. If _envRec_.[[IsWithEnvironment]] is *false*, return *true*.
1. Let _unscopables_ be ? Get(_bindingObject_, @@unscopables).
1. If Type(_unscopables_) is Object, then
1. Let _blocked_ be ! ToBoolean(? Get(_unscopables_, _N_)).
1. If _blocked_ is *true*, return *false*.
Expand All @@ -8586,8 +8626,8 @@ <h1>HasBinding ( _N_ )</h1>
<h1>CreateMutableBinding ( _N_, _D_ )</h1>
<p>The CreateMutableBinding concrete method of an object Environment Record _envRec_ takes arguments _N_ (a String) and _D_ (a Boolean). It creates in an Environment Record's associated binding object a property whose name is the String value and initializes it to the value *undefined*. If _D_ has the value *true*, the new property's [[Configurable]] attribute is set to *true*; otherwise it is set to *false*. It performs the following steps when called:</p>
<emu-alg>
1. Let _bindings_ be the binding object for _envRec_.
1. Return ? DefinePropertyOrThrow(_bindings_, _N_, PropertyDescriptor { [[Value]]: *undefined*, [[Writable]]: *true*, [[Enumerable]]: *true*, [[Configurable]]: _D_ }).
1. Let _bindingObject_ be _envRec_.[[BindingObject]].
1. Return ? DefinePropertyOrThrow(_bindingObject_, _N_, PropertyDescriptor { [[Value]]: *undefined*, [[Writable]]: *true*, [[Enumerable]]: *true*, [[Configurable]]: _D_ }).
</emu-alg>
<emu-note>
<p>Normally _envRec_ will not have a binding for _N_ but if it does, the semantics of DefinePropertyOrThrow may result in an existing binding being replaced or shadowed or cause an abrupt completion to be returned.</p>
Expand All @@ -8614,31 +8654,31 @@ <h1>InitializeBinding ( _N_, _V_ )</h1>
<h1>SetMutableBinding ( _N_, _V_, _S_ )</h1>
<p>The SetMutableBinding concrete method of an object Environment Record _envRec_ takes arguments _N_ (a String), _V_ (an ECMAScript language value), and _S_ (a Boolean). It attempts to set the value of the Environment Record's associated binding object's property whose name is the value of the argument _N_ to the value of argument _V_. A property named _N_ normally already exists but if it does not or is not currently writable, error handling is determined by _S_. It performs the following steps when called:</p>
<emu-alg>
1. Let _bindings_ be the binding object for _envRec_.
1. Let _stillExists_ be ? HasProperty(_bindings_, _N_).
1. Let _bindingObject_ be _envRec_.[[BindingObject]].
1. Let _stillExists_ be ? HasProperty(_bindingObject_, _N_).
1. If _stillExists_ is *false* and _S_ is *true*, throw a *ReferenceError* exception.
1. Return ? Set(_bindings_, _N_, _V_, _S_).
1. Return ? Set(_bindingObject_, _N_, _V_, _S_).
</emu-alg>
</emu-clause>

jmdyck marked this conversation as resolved.
Show resolved Hide resolved
<emu-clause id="sec-object-environment-records-getbindingvalue-n-s">
<h1>GetBindingValue ( _N_, _S_ )</h1>
<p>The GetBindingValue concrete method of an object Environment Record _envRec_ takes arguments _N_ (a String) and _S_ (a Boolean). It returns the value of its associated binding object's property whose name is the String value of the argument identifier _N_. The property should already exist but if it does not the result depends upon _S_. It performs the following steps when called:</p>
<emu-alg>
1. Let _bindings_ be the binding object for _envRec_.
1. Let _value_ be ? HasProperty(_bindings_, _N_).
1. Let _bindingObject_ be _envRec_.[[BindingObject]].
1. Let _value_ be ? HasProperty(_bindingObject_, _N_).
jmdyck marked this conversation as resolved.
Show resolved Hide resolved
1. If _value_ is *false*, then
1. If _S_ is *false*, return the value *undefined*; otherwise throw a *ReferenceError* exception.
1. Return ? Get(_bindings_, _N_).
1. Return ? Get(_bindingObject_, _N_).
</emu-alg>
</emu-clause>

<emu-clause id="sec-object-environment-records-deletebinding-n">
<h1>DeleteBinding ( _N_ )</h1>
<p>The DeleteBinding concrete method of an object Environment Record _envRec_ takes argument _N_ (a String). It can only delete bindings that correspond to properties of the environment object whose [[Configurable]] attribute have the value *true*. It performs the following steps when called:</p>
<emu-alg>
1. Let _bindings_ be the binding object for _envRec_.
1. Return ? _bindings_.[[Delete]](_N_).
1. Let _bindingObject_ be _envRec_.[[BindingObject]].
1. Return ? _bindingObject_.[[Delete]](_N_).
</emu-alg>
</emu-clause>

Expand Down Expand Up @@ -8668,7 +8708,7 @@ <h1>HasSuperBinding ( )</h1>
<h1>WithBaseObject ( )</h1>
<p>The WithBaseObject concrete method of an object Environment Record _envRec_ takes no arguments. It performs the following steps when called:</p>
<emu-alg>
1. If the _withEnvironment_ flag of _envRec_ is *true*, return the binding object for _envRec_.
1. If _envRec_.[[IsWithEnvironment]] is *true*, return _envRec_.[[BindingObject]].
1. Otherwise, return *undefined*.
</emu-alg>
</emu-clause>
Expand Down Expand Up @@ -9054,7 +9094,7 @@ <h1>DeleteBinding ( _N_ )</h1>
1. If _DclRec_.HasBinding(_N_) is *true*, then
1. Return _DclRec_.DeleteBinding(_N_).
1. Let _ObjRec_ be _envRec_.[[ObjectRecord]].
1. Let _globalObject_ be the binding object for _ObjRec_.
1. Let _globalObject_ be _ObjRec_.[[BindingObject]].
1. Let _existingProp_ be ? HasOwnProperty(_globalObject_, _N_).
1. If _existingProp_ is *true*, then
1. Let _status_ be ? _ObjRec_.DeleteBinding(_N_).
Expand Down Expand Up @@ -9128,7 +9168,7 @@ <h1>HasRestrictedGlobalProperty ( _N_ )</h1>
<p>The HasRestrictedGlobalProperty concrete method of a global Environment Record _envRec_ takes argument _N_ (a String). It determines if the argument identifier is the name of a property of the global object that must not be shadowed by a global lexical binding. It performs the following steps when called:</p>
<emu-alg>
1. Let _ObjRec_ be _envRec_.[[ObjectRecord]].
1. Let _globalObject_ be the binding object for _ObjRec_.
1. Let _globalObject_ be _ObjRec_.[[BindingObject]].
1. Let _existingProp_ be ? _globalObject_.[[GetOwnProperty]](_N_).
1. If _existingProp_ is *undefined*, return *false*.
1. If _existingProp_.[[Configurable]] is *true*, return *false*.
Expand All @@ -9144,7 +9184,7 @@ <h1>CanDeclareGlobalVar ( _N_ )</h1>
<p>The CanDeclareGlobalVar concrete method of a global Environment Record _envRec_ takes argument _N_ (a String). It determines if a corresponding CreateGlobalVarBinding call would succeed if called for the same argument _N_. Redundant var declarations and var declarations for pre-existing global object properties are allowed. It performs the following steps when called:</p>
<emu-alg>
1. Let _ObjRec_ be _envRec_.[[ObjectRecord]].
1. Let _globalObject_ be the binding object for _ObjRec_.
1. Let _globalObject_ be _ObjRec_.[[BindingObject]].
1. Let _hasProperty_ be ? HasOwnProperty(_globalObject_, _N_).
1. If _hasProperty_ is *true*, return *true*.
1. Return ? IsExtensible(_globalObject_).
Expand All @@ -9156,7 +9196,7 @@ <h1>CanDeclareGlobalFunction ( _N_ )</h1>
<p>The CanDeclareGlobalFunction concrete method of a global Environment Record _envRec_ takes argument _N_ (a String). It determines if a corresponding CreateGlobalFunctionBinding call would succeed if called for the same argument _N_. It performs the following steps when called:</p>
<emu-alg>
1. Let _ObjRec_ be _envRec_.[[ObjectRecord]].
1. Let _globalObject_ be the binding object for _ObjRec_.
1. Let _globalObject_ be _ObjRec_.[[BindingObject]].
1. Let _existingProp_ be ? _globalObject_.[[GetOwnProperty]](_N_).
1. If _existingProp_ is *undefined*, return ? IsExtensible(_globalObject_).
1. If _existingProp_.[[Configurable]] is *true*, return *true*.
Expand All @@ -9170,7 +9210,7 @@ <h1>CreateGlobalVarBinding ( _N_, _D_ )</h1>
<p>The CreateGlobalVarBinding concrete method of a global Environment Record _envRec_ takes arguments _N_ (a String) and _D_ (a Boolean). It creates and initializes a mutable binding in the associated object Environment Record and records the bound name in the associated [[VarNames]] List. If a binding already exists, it is reused and assumed to be initialized. It performs the following steps when called:</p>
<emu-alg>
1. Let _ObjRec_ be _envRec_.[[ObjectRecord]].
1. Let _globalObject_ be the binding object for _ObjRec_.
1. Let _globalObject_ be _ObjRec_.[[BindingObject]].
1. Let _hasProperty_ be ? HasOwnProperty(_globalObject_, _N_).
1. Let _extensible_ be ? IsExtensible(_globalObject_).
1. If _hasProperty_ is *false* and _extensible_ is *true*, then
Expand All @@ -9188,7 +9228,7 @@ <h1>CreateGlobalFunctionBinding ( _N_, _V_, _D_ )</h1>
<p>The CreateGlobalFunctionBinding concrete method of a global Environment Record _envRec_ takes arguments _N_ (a String), _V_ (an ECMAScript language value), and _D_ (a Boolean). It creates and initializes a mutable binding in the associated object Environment Record and records the bound name in the associated [[VarNames]] List. If a binding already exists, it is replaced. It performs the following steps when called:</p>
<emu-alg>
1. Let _ObjRec_ be _envRec_.[[ObjectRecord]].
1. Let _globalObject_ be the binding object for _ObjRec_.
1. Let _globalObject_ be _ObjRec_.[[BindingObject]].
1. Let _existingProp_ be ? _globalObject_.[[GetOwnProperty]](_N_).
1. If _existingProp_ is *undefined* or _existingProp_.[[Configurable]] is *true*, then
1. Let _desc_ be the PropertyDescriptor { [[Value]]: _V_, [[Writable]]: *true*, [[Enumerable]]: *true*, [[Configurable]]: _D_ }.
Expand Down Expand Up @@ -9333,10 +9373,12 @@ <h1>NewDeclarativeEnvironment ( _E_ )</h1>
</emu-clause>

<emu-clause id="sec-newobjectenvironment" aoid="NewObjectEnvironment">
<h1>NewObjectEnvironment ( _O_, _E_ )</h1>
<p>The abstract operation NewObjectEnvironment takes arguments _O_ (an Object) and _E_ (an Environment Record). It performs the following steps when called:</p>
<h1>NewObjectEnvironment ( _O_, _W_, _E_ )</h1>
<p>The abstract operation NewObjectEnvironment takes arguments _O_ (an Object), _W_ (a Boolean), and _E_ (an Environment Record or *null*). It performs the following steps when called:</p>
<emu-alg>
1. Let _env_ be a new object Environment Record containing _O_ as the binding object.
1. Let _env_ be a new object Environment Record.
1. Set _env_.[[BindingObject]] to _O_.
1. Set _env_.[[IsWithEnvironment]] to _W_.
1. Set _env_.[[OuterEnv]] to _E_.
1. Return _env_.
</emu-alg>
Expand All @@ -9362,7 +9404,7 @@ <h1>NewFunctionEnvironment ( _F_, _newTarget_ )</h1>
<h1>NewGlobalEnvironment ( _G_, _thisValue_ )</h1>
<p>The abstract operation NewGlobalEnvironment takes arguments _G_ and _thisValue_. It performs the following steps when called:</p>
<emu-alg>
1. Let _objRec_ be a new object Environment Record containing _G_ as the binding object.
1. Let _objRec_ be NewObjectEnvironment(_G_, *false*, *null*).
1. Let _dclRec_ be a new declarative Environment Record containing no bindings.
1. Let _env_ be a new global Environment Record.
1. Set _env_.[[ObjectRecord]] to _objRec_.
Expand Down Expand Up @@ -18901,8 +18943,7 @@ <h1>Runtime Semantics: Evaluation</h1>
1. Let _val_ be the result of evaluating |Expression|.
1. Let _obj_ be ? ToObject(? GetValue(_val_)).
1. Let _oldEnv_ be the running execution context's LexicalEnvironment.
1. Let _newEnv_ be NewObjectEnvironment(_obj_, _oldEnv_).
1. Set the _withEnvironment_ flag of _newEnv_ to *true*.
1. Let _newEnv_ be NewObjectEnvironment(_obj_, *true*, _oldEnv_).
1. Set the running execution context's LexicalEnvironment to _newEnv_.
1. Let _C_ be the result of evaluating |Statement|.
1. Set the running execution context's LexicalEnvironment to _oldEnv_.
Expand Down