Stage 3 Draft / January 27, 2021

Private Fields in in

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12 ECMAScript Language: Expressions

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12.10 Relational Operators

Note 1

The result of evaluating a relational operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.

Syntax

RelationalExpression[In, Yield, Await]:ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]<ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]>ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]<=ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]>=ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]instanceofShiftExpression[?Yield, ?Await] [+In]RelationalExpression[+In, ?Yield, ?Await]inShiftExpression[?Yield, ?Await] [+In]PrivateIdentifierinShiftExpression[?Yield, ?Await] Note 2

The [In] grammar parameter is needed to avoid confusing the in operator in a relational expression with the in operator in a for statement.

12.10.1 Static Semantics: IsFunctionDefinition

RelationalExpression:RelationalExpression<ShiftExpression RelationalExpression>ShiftExpression RelationalExpression<=ShiftExpression RelationalExpression>=ShiftExpression RelationalExpressioninstanceofShiftExpression RelationalExpressioninShiftExpression PrivateIdentifierinShiftExpression
  1. Return false.

12.10.2 Static Semantics: AssignmentTargetType

RelationalExpression:RelationalExpression<ShiftExpression RelationalExpression>ShiftExpression RelationalExpression<=ShiftExpression RelationalExpression>=ShiftExpression RelationalExpressioninstanceofShiftExpression RelationalExpressioninShiftExpression PrivateIdentifierinShiftExpression
  1. Return invalid.
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12.10.3 Runtime Semantics: Evaluation

RelationalExpression:PrivateIdentifierinShiftExpression
  1. Let privateIdentifier be the StringValue of PrivateIdentifier.
  2. Let rref be the result of evaluating ShiftExpression.
  3. Let rval be ? GetValue(rref).
  4. If Type(rval) is not Object, throw a TypeError exception.
  5. Let env be the running execution context's PrivateEnvironment.
  6. Let privateNameBinding be ? ResolveBinding(privateIdentifier, env).
  7. Let privateName be ? GetValue(privateNameBinding).
  8. Assert: privateName is a Private Name.
  9. If privateName.[[Kind]] is "field",
    1. If ! PrivateFieldFind(privateName, rval) is not empty, then return true.
  10. Else,
    1. Assert: privateName.[[Kind]] is "method" or "accessor".
    2. If PrivateBrandCheck(rval, privateName) is not an abrupt completion, then return true.
  11. Return false.
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12.10.5 Static Semantics: AllPrivateIdentifiersValid

AllPrivateIdentifiersValid is an abstract operation which takes names as an argument.

RelationalExpression:PrivateIdentifierinShiftExpression
  1. If StringValue of PrivateIdentifier is in names, return true.
  2. Return false.

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14 ECMAScript Language: Functions and Classes

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14.9 Tail Position Calls

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14.9.2 Static Semantics: HasCallInTailPosition

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14.9.2.1 Expression Rules

Note

A potential tail position call that is immediately followed by return GetValue of the call result is also a possible tail position call. Function calls cannot return reference values, so such a GetValue operation will always return the same value as the actual function call result.

AssignmentExpression:YieldExpression ArrowFunction AsyncArrowFunction LeftHandSideExpression=AssignmentExpression LeftHandSideExpressionAssignmentOperatorAssignmentExpression BitwiseANDExpression:BitwiseANDExpression&EqualityExpression BitwiseXORExpression:BitwiseXORExpression^BitwiseANDExpression BitwiseORExpression:BitwiseORExpression|BitwiseXORExpression EqualityExpression:EqualityExpression==RelationalExpression EqualityExpression!=RelationalExpression EqualityExpression===RelationalExpression EqualityExpression!==RelationalExpression RelationalExpression:RelationalExpression<ShiftExpression RelationalExpression>ShiftExpression RelationalExpression<=ShiftExpression RelationalExpression>=ShiftExpression RelationalExpressioninstanceofShiftExpression RelationalExpressioninShiftExpression PrivateIdentifierinShiftExpression ShiftExpression:ShiftExpression<<AdditiveExpression ShiftExpression>>AdditiveExpression ShiftExpression>>>AdditiveExpression AdditiveExpression:AdditiveExpression+MultiplicativeExpression AdditiveExpression-MultiplicativeExpression MultiplicativeExpression:MultiplicativeExpressionMultiplicativeOperatorExponentiationExpression ExponentiationExpression:UpdateExpression**ExponentiationExpression UpdateExpression:LeftHandSideExpression++ LeftHandSideExpression-- ++UnaryExpression --UnaryExpression UnaryExpression:deleteUnaryExpression voidUnaryExpression typeofUnaryExpression +UnaryExpression -UnaryExpression ~UnaryExpression !UnaryExpression AwaitExpression CallExpression:SuperCall CallExpression[Expression] CallExpression.IdentifierName NewExpression:newNewExpression MemberExpression:MemberExpression[Expression] MemberExpression.IdentifierName SuperProperty MetaProperty newMemberExpressionArguments PrimaryExpression:this IdentifierReference Literal ArrayLiteral ObjectLiteral FunctionExpression ClassExpression GeneratorExpression AsyncFunctionExpression AsyncGeneratorExpression RegularExpressionLiteral TemplateLiteral
  1. Return false.
Expression:AssignmentExpression Expression,AssignmentExpression
  1. Return HasCallInTailPosition of AssignmentExpression with argument call.
ConditionalExpression:ShortCircuitExpression?AssignmentExpression:AssignmentExpression
  1. Let has be HasCallInTailPosition of the first AssignmentExpression with argument call.
  2. If has is true, return true.
  3. Return HasCallInTailPosition of the second AssignmentExpression with argument call.
LogicalANDExpression:LogicalANDExpression&&BitwiseORExpression
  1. Return HasCallInTailPosition of BitwiseORExpression with argument call.
LogicalORExpression:LogicalORExpression||LogicalANDExpression
  1. Return HasCallInTailPosition of LogicalANDExpression with argument call.
CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
  1. Return HasCallInTailPosition of BitwiseORExpression with argument call.
CallExpression:CoverCallExpressionAndAsyncArrowHead CallExpressionArguments CallExpressionTemplateLiteral
  1. If this CallExpression is call, return true.
  2. Return false.
OptionalExpression:MemberExpressionOptionalChain CallExpressionOptionalChain OptionalExpressionOptionalChain
  1. Return HasCallInTailPosition of OptionalChain with argument call.
OptionalChain:?.[Expression] ?.IdentifierName OptionalChain[Expression] OptionalChain.IdentifierName
  1. Return false.
OptionalChain:?.Arguments OptionalChainArguments
  1. If this OptionalChain is call, return true.
  2. Return false.
MemberExpression:MemberExpressionTemplateLiteral
  1. If this MemberExpression is call, return true.
  2. Return false.
PrimaryExpression:CoverParenthesizedExpressionAndArrowParameterList
  1. Let expr be CoveredParenthesizedExpression of CoverParenthesizedExpressionAndArrowParameterList.
  2. Return HasCallInTailPosition of expr with argument call.
ParenthesizedExpression:(Expression)
  1. Return HasCallInTailPosition of Expression with argument call.

A Grammar Summary

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A.2 Expressions

... RelationalExpression[In, Yield, Await]:ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]<ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]>ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]<=ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]>=ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await]instanceofShiftExpression[?Yield, ?Await] [+In]RelationalExpression[+In, ?Yield, ?Await]inShiftExpression[?Yield, ?Await] [+In]PrivateIdentifierinShiftExpression[?Yield, ?Await]

B Copyright & Software License

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© 2021 Jordan Harband

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