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spec.emu
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<!doctype html>
<meta charset="utf8">
<link rel="stylesheet" href="./spec.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/8.4/styles/github.min.css">
<script src="./spec.js"></script>
<pre class="metadata">
title: Optional Chaining Assignment
stage: 1
contributors: Nicolò Ribaudo
</pre>
<emu-clause id="sec-assignment-operators">
<h1>Assignment Operators</h1>
<emu-clause id="sec-static-semantics-assignmenttargettype" type="sdo">
<h1>
Static Semantics: AssignmentTargetType (
): ~simple~, ~optional~, or ~invalid~
</h1>
<dl class="header">
</dl>
<emu-grammar>IdentifierReference : Identifier</emu-grammar>
<emu-alg>
1. If this |IdentifierReference| is contained in strict mode code and StringValue of |Identifier| is either *"eval"* or *"arguments"*, return ~invalid~.
1. Return ~simple~.
</emu-alg>
<emu-grammar>
IdentifierReference :
`yield`
`await`
CallExpression :
CallExpression `[` Expression `]`
CallExpression `.` IdentifierName
CallExpression `.` PrivateIdentifier
MemberExpression :
MemberExpression `[` Expression `]`
MemberExpression `.` IdentifierName
SuperProperty
MemberExpression `.` PrivateIdentifier
</emu-grammar>
<emu-alg>
1. Return ~simple~.
</emu-alg>
<emu-grammar><ins>
OptionalExpression :
MemberExpression OptionalChain
CallExpression OptionalChain
OptionalExpression OptionalChain
</ins></emu-grammar>
<emu-alg>
1. <ins>Return AssignmentTargetType of |OptionalChain|.</ins>
</emu-alg>
<emu-grammar><ins>
OptionalChain :
`?.` `[` Expression `]`
`?.` IdentifierName
`?.` PrivateIdentifier
OptionalChain `[` Expression `]`
OptionalChain `.` IdentifierName
OptionalChain `.` PrivateIdentifier
</ins></emu-grammar>
<emu-alg>
1. <ins>Return ~optional~.</ins>
</emu-alg>
<emu-grammar>
PrimaryExpression :
CoverParenthesizedExpressionAndArrowParameterList
</emu-grammar>
<emu-alg>
1. Let _expr_ be the |ParenthesizedExpression| that is covered by |CoverParenthesizedExpressionAndArrowParameterList|.
1. Return AssignmentTargetType of _expr_.
</emu-alg>
<emu-grammar>
PrimaryExpression :
`this`
Literal
ArrayLiteral
ObjectLiteral
FunctionExpression
ClassExpression
GeneratorExpression
AsyncFunctionExpression
AsyncGeneratorExpression
RegularExpressionLiteral
TemplateLiteral
CallExpression :
CoverCallExpressionAndAsyncArrowHead
SuperCall
ImportCall
CallExpression Arguments
CallExpression TemplateLiteral
<ins>
OptionalChain :
`?.` Arguments
`?.` TemplateLiteral
OptionalChain Arguments
OptionalChain TemplateLiteral
</ins>
NewExpression :
`new` NewExpression
MemberExpression :
MemberExpression TemplateLiteral
`new` MemberExpression Arguments
NewTarget :
`new` `.` `target`
ImportMeta :
`import` `.` `meta`
<del>
LeftHandSideExpression :
OptionalExpression
</del>
UpdateExpression :
LeftHandSideExpression `++`
LeftHandSideExpression `--`
`++` UnaryExpression
`--` UnaryExpression
UnaryExpression :
`delete` UnaryExpression
`void` UnaryExpression
`typeof` UnaryExpression
`+` UnaryExpression
`-` UnaryExpression
`~` UnaryExpression
`!` UnaryExpression
AwaitExpression
ExponentiationExpression :
UpdateExpression `**` ExponentiationExpression
MultiplicativeExpression :
MultiplicativeExpression MultiplicativeOperator ExponentiationExpression
AdditiveExpression :
AdditiveExpression `+` MultiplicativeExpression
AdditiveExpression `-` MultiplicativeExpression
ShiftExpression :
ShiftExpression `<<` AdditiveExpression
ShiftExpression `>>` AdditiveExpression
ShiftExpression `>>>` AdditiveExpression
RelationalExpression :
RelationalExpression `<` ShiftExpression
RelationalExpression `>` ShiftExpression
RelationalExpression `<=` ShiftExpression
RelationalExpression `>=` ShiftExpression
RelationalExpression `instanceof` ShiftExpression
RelationalExpression `in` ShiftExpression
PrivateIdentifier `in` ShiftExpression
EqualityExpression :
EqualityExpression `==` RelationalExpression
EqualityExpression `!=` RelationalExpression
EqualityExpression `===` RelationalExpression
EqualityExpression `!==` RelationalExpression
BitwiseANDExpression :
BitwiseANDExpression `&` EqualityExpression
BitwiseXORExpression :
BitwiseXORExpression `^` BitwiseANDExpression
BitwiseORExpression :
BitwiseORExpression `|` BitwiseXORExpression
LogicalANDExpression :
LogicalANDExpression `&&` BitwiseORExpression
LogicalORExpression :
LogicalORExpression `||` LogicalANDExpression
CoalesceExpression :
CoalesceExpressionHead `??` BitwiseORExpression
ConditionalExpression :
ShortCircuitExpression `?` AssignmentExpression `:` AssignmentExpression
AssignmentExpression :
YieldExpression
ArrowFunction
AsyncArrowFunction
LeftHandSideExpression `=` AssignmentExpression
LeftHandSideExpression AssignmentOperator AssignmentExpression
LeftHandSideExpression `&&=` AssignmentExpression
LeftHandSideExpression `||=` AssignmentExpression
LeftHandSideExpression `??=` AssignmentExpression
Expression :
Expression `,` AssignmentExpression
</emu-grammar>
<emu-alg>
1. Return ~invalid~.
</emu-alg>
</emu-clause>
<emu-clause id="sec-assignment-operators-static-semantics-early-errors">
<h1>Static Semantics: Early Errors</h1>
<emu-grammar>AssignmentExpression : LeftHandSideExpression `=` AssignmentExpression</emu-grammar>
<p>If |LeftHandSideExpression| is either an |ObjectLiteral| or an |ArrayLiteral|, the following Early Error rules are applied:</p>
<ul>
<li>
|LeftHandSideExpression| must cover an |AssignmentPattern|.
</li>
</ul>
<p>If |LeftHandSideExpression| is neither an |ObjectLiteral| nor an |ArrayLiteral|, the following Early Error rule is applied:</p>
<ul>
<li>
It is a Syntax Error if AssignmentTargetType of |LeftHandSideExpression| is not ~simple~ <ins>or ~optional~</ins>.
</li>
</ul>
<emu-grammar>
AssignmentExpression :
LeftHandSideExpression AssignmentOperator AssignmentExpression
LeftHandSideExpression `&&=` AssignmentExpression
LeftHandSideExpression `||=` AssignmentExpression
LeftHandSideExpression `??=` AssignmentExpression
</emu-grammar>
<ul>
<li>
It is a Syntax Error if AssignmentTargetType of |LeftHandSideExpression| is not ~simple~ <ins>or ~optional~</ins>.
</li>
</ul>
</emu-clause>
<emu-clause id="sec-assignment-operators-runtime-semantics-evaluation" type="sdo">
<h1>Runtime Semantics: Evaluation</h1>
<emu-grammar>AssignmentExpression : LeftHandSideExpression `=` AssignmentExpression</emu-grammar>
<emu-alg>
1. If |LeftHandSideExpression| is neither an |ObjectLiteral| nor an |ArrayLiteral|, then
1. Let _lref_ be ? Evaluation of |LeftHandSideExpression|.
1. <ins>If _lref_ is *undefined* and |LeftHandSideExpression| is not a |ParenthesizedExpression|, return *undefined*.</ins>
1. If IsAnonymousFunctionDefinition(|AssignmentExpression|) and IsIdentifierRef of |LeftHandSideExpression| are both *true*, then
1. Let _rval_ be ? NamedEvaluation of |AssignmentExpression| with argument _lref_.[[ReferencedName]].
1. Else,
1. Let _rref_ be ? Evaluation of |AssignmentExpression|.
1. Let _rval_ be ? GetValue(_rref_).
1. <ins>If _lref_ is *undefined*, throw a *TypeError* exception.</ins>
1. [id="step-assignmentexpression-evaluation-simple-putvalue"] Perform ? PutValue(_lref_, _rval_).
1. Return _rval_.
1. Let _assignmentPattern_ be the |AssignmentPattern| that is covered by |LeftHandSideExpression|.
1. Let _rref_ be ? Evaluation of |AssignmentExpression|.
1. Let _rval_ be ? GetValue(_rref_).
1. Perform ? DestructuringAssignmentEvaluation of _assignmentPattern_ with argument _rval_.
1. Return _rval_.
</emu-alg>
<emu-grammar>AssignmentExpression : LeftHandSideExpression AssignmentOperator AssignmentExpression</emu-grammar>
<emu-alg>
1. Let _lref_ be ? Evaluation of |LeftHandSideExpression|.
1. <ins>If _lref_ is *undefined*, then</ins>
1. <ins>If |LeftHandSideExpression| is a |ParenthesizedExpression|, throw a *TypeError* exception.</ins>
1. <ins>Return *undefined*.</ins>
1. [id="step-assignmentexpression-evaluation-compound-getvalue"] Let _lval_ be ? GetValue(_lref_).
1. Let _rref_ be ? Evaluation of |AssignmentExpression|.
1. Let _rval_ be ? GetValue(_rref_).
1. Let _assignmentOpText_ be the source text matched by |AssignmentOperator|.
1. Let _opText_ be the sequence of Unicode code points associated with _assignmentOpText_ in the following table:
<figure>
<!-- emu-format ignore -->
<table class="lightweight-table">
<tr><th> _assignmentOpText_ </th><th> _opText_ </th></tr>
<tr><td> `**=` </td><td> `**` </td></tr>
<tr><td> `*=` </td><td> `*` </td></tr>
<tr><td> `/=` </td><td> `/` </td></tr>
<tr><td> `%=` </td><td> `%` </td></tr>
<tr><td> `+=` </td><td> `+` </td></tr>
<tr><td> `-=` </td><td> `-` </td></tr>
<tr><td> `<<=` </td><td> `<<` </td></tr>
<tr><td> `>>=` </td><td> `>>` </td></tr>
<tr><td> `>>>=` </td><td> `>>>` </td></tr>
<tr><td> `&=` </td><td> `&` </td></tr>
<tr><td> `^=` </td><td> `^` </td></tr>
<tr><td> `|=` </td><td> `|` </td></tr>
</table>
</figure>
1. Let _r_ be ? ApplyStringOrNumericBinaryOperator(_lval_, _opText_, _rval_).
1. [id="step-assignmentexpression-evaluation-compound-putvalue"] Perform ? PutValue(_lref_, _r_).
1. Return _r_.
</emu-alg>
<emu-grammar>AssignmentExpression : LeftHandSideExpression `&&=` AssignmentExpression</emu-grammar>
<emu-alg>
1. Let _lref_ be ? Evaluation of |LeftHandSideExpression|.
1. <ins>If _lref_ is *undefined*, then</ins>
1. <ins>If |LeftHandSideExpression| is a |ParenthesizedExpression|, throw a *TypeError* exception.</ins>
1. <ins>Return *undefined*.</ins>
1. [id="step-assignmentexpression-evaluation-lgcl-and-getvalue"] Let _lval_ be ? GetValue(_lref_).
1. Let _lbool_ be ToBoolean(_lval_).
1. If _lbool_ is *false*, return _lval_.
1. If IsAnonymousFunctionDefinition(|AssignmentExpression|) is *true* and IsIdentifierRef of |LeftHandSideExpression| is *true*, then
1. Let _rval_ be ? NamedEvaluation of |AssignmentExpression| with argument _lref_.[[ReferencedName]].
1. Else,
1. Let _rref_ be ? Evaluation of |AssignmentExpression|.
1. Let _rval_ be ? GetValue(_rref_).
1. [id="step-assignmentexpression-evaluation-lgcl-and-putvalue"] Perform ? PutValue(_lref_, _rval_).
1. Return _rval_.
</emu-alg>
<emu-grammar>AssignmentExpression : LeftHandSideExpression `||=` AssignmentExpression</emu-grammar>
<emu-alg>
1. Let _lref_ be ? Evaluation of |LeftHandSideExpression|.
1. <ins>If _lref_ is *undefined*, then</ins>
1. <ins>If |LeftHandSideExpression| is a |ParenthesizedExpression|, throw a *TypeError* exception.</ins>
1. <ins>Return *undefined*.</ins>
1. [id="step-assignmentexpression-evaluation-lgcl-or-getvalue"] Let _lval_ be ? GetValue(_lref_).
1. Let _lbool_ be ToBoolean(_lval_).
1. If _lbool_ is *true*, return _lval_.
1. If IsAnonymousFunctionDefinition(|AssignmentExpression|) is *true* and IsIdentifierRef of |LeftHandSideExpression| is *true*, then
1. Let _rval_ be ? NamedEvaluation of |AssignmentExpression| with argument _lref_.[[ReferencedName]].
1. Else,
1. Let _rref_ be ? Evaluation of |AssignmentExpression|.
1. Let _rval_ be ? GetValue(_rref_).
1. [id="step-assignmentexpression-evaluation-lgcl-or-putvalue"] Perform ? PutValue(_lref_, _rval_).
1. Return _rval_.
</emu-alg>
<emu-grammar>AssignmentExpression : LeftHandSideExpression `??=` AssignmentExpression</emu-grammar>
<emu-alg>
1. Let _lref_ be ? Evaluation of |LeftHandSideExpression|.
1. <ins>If _lref_ is *undefined*, then</ins>
1. <ins>If |LeftHandSideExpression| is a |ParenthesizedExpression|, throw a *TypeError* exception.</ins>
1. <ins>Return *undefined*.</ins>
1. [id="step-assignmentexpression-evaluation-lgcl-nullish-getvalue"] Let _lval_ be ? GetValue(_lref_).
1. If _lval_ is neither *undefined* nor *null*, return _lval_.
1. If IsAnonymousFunctionDefinition(|AssignmentExpression|) is *true* and IsIdentifierRef of |LeftHandSideExpression| is *true*, then
1. Let _rval_ be ? NamedEvaluation of |AssignmentExpression| with argument _lref_.[[ReferencedName]].
1. Else,
1. Let _rref_ be ? Evaluation of |AssignmentExpression|.
1. Let _rval_ be ? GetValue(_rref_).
1. [id="step-assignmentexpression-evaluation-lgcl-nullish-putvalue"] Perform ? PutValue(_lref_, _rval_).
1. Return _rval_.
</emu-alg>
</emu-clause>
</emu-clause>