ECMAScript® 2021 Language Specification

Draft ECMA-262 / February 25, 2021

8.2 Labels

8.2.1 Static Semantics: ContainsDuplicateLabels

With parameter labelSet.

Statement : VariableStatement EmptyStatement ExpressionStatement ContinueStatement BreakStatement ReturnStatement ThrowStatement DebuggerStatement Block : { } StatementListItem : Declaration
  1. Return false.
 StatementList : StatementList StatementListItem
  1. Let hasDuplicates be ContainsDuplicateLabels of StatementList with argument labelSet.
  2. If hasDuplicates is true, return true.
  3. Return ContainsDuplicateLabels of StatementListItem with argument labelSet.
 IfStatement : if ( Expression ) Statement else Statement
  1. Let hasDuplicate be ContainsDuplicateLabels of the first Statement with argument labelSet.
  2. If hasDuplicate is true, return true.
  3. Return ContainsDuplicateLabels of the second Statement with argument labelSet.
 IfStatement : if ( Expression ) Statement
  1. Return ContainsDuplicateLabels of Statement with argument labelSet.
 DoWhileStatement : do Statement while ( Expression ) ;
  1. Return ContainsDuplicateLabels of Statement with argument labelSet.
 WhileStatement : while ( Expression ) Statement
  1. Return ContainsDuplicateLabels of Statement with argument labelSet.
 ForStatement : for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
  1. Return ContainsDuplicateLabels of Statement with argument labelSet.
 ForInOfStatement : for ( LeftHandSideExpression in Expression ) Statement for ( var ForBinding in Expression ) Statement for ( ForDeclaration in Expression ) Statement for ( LeftHandSideExpression of AssignmentExpression ) Statement for ( var ForBinding of AssignmentExpression ) Statement for ( ForDeclaration of AssignmentExpression ) Statement for await ( LeftHandSideExpression of AssignmentExpression ) Statement for await ( var ForBinding of AssignmentExpression ) Statement for await ( ForDeclaration of AssignmentExpression ) Statement
  1. Return ContainsDuplicateLabels of Statement with argument labelSet.
 Note

This section is extended by Annex B.3.6.

 WithStatement : with ( Expression ) Statement
  1. Return ContainsDuplicateLabels of Statement with argument labelSet.
 SwitchStatement : switch ( Expression ) CaseBlock
  1. Return ContainsDuplicateLabels of CaseBlock with argument labelSet.
 CaseBlock : { }
  1. Return false.
 CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
  1. If the first CaseClauses is present, then
    1. Let hasDuplicates be ContainsDuplicateLabels of the first CaseClauses with argument labelSet.
    2. If hasDuplicates is true, return true.
  2. Let hasDuplicates be ContainsDuplicateLabels of DefaultClause with argument labelSet.
  3. If hasDuplicates is true, return true.
  4. If the second CaseClauses is not present, return false.
  5. Return ContainsDuplicateLabels of the second CaseClauses with argument labelSet.
 CaseClauses : CaseClauses CaseClause
  1. Let hasDuplicates be ContainsDuplicateLabels of CaseClauses with argument labelSet.
  2. If hasDuplicates is true, return true.
  3. Return ContainsDuplicateLabels of CaseClause with argument labelSet.
 CaseClause : case Expression : StatementListopt
  1. If the StatementList is present, return ContainsDuplicateLabels of StatementList with argument labelSet.
  2. Return false.
 DefaultClause : default : StatementListopt
  1. If the StatementList is present, return ContainsDuplicateLabels of StatementList with argument labelSet.
  2. Return false.
 LabelledStatement : LabelIdentifier : LabelledItem
  1. Let label be the StringValue of LabelIdentifier.
  2. If label is an element of labelSet, return true.
  3. Let newLabelSet be a copy of labelSet with label appended.
  4. Return ContainsDuplicateLabels of LabelledItem with argument newLabelSet.
 LabelledItem : FunctionDeclaration
  1. Return false.
 TryStatement : try Block Catch
  1. Let hasDuplicates be ContainsDuplicateLabels of Block with argument labelSet.
  2. If hasDuplicates is true, return true.
  3. Return ContainsDuplicateLabels of Catch with argument labelSet.
 TryStatement : try Block Finally
  1. Let hasDuplicates be ContainsDuplicateLabels of Block with argument labelSet.
  2. If hasDuplicates is true, return true.
  3. Return ContainsDuplicateLabels of Finally with argument labelSet.
 TryStatement : try Block Catch Finally
  1. Let hasDuplicates be ContainsDuplicateLabels of Block with argument labelSet.
  2. If hasDuplicates is true, return true.
  3. Let hasDuplicates be ContainsDuplicateLabels of Catch with argument labelSet.
  4. If hasDuplicates is true, return true.
  5. Return ContainsDuplicateLabels of Finally with argument labelSet.
 Catch : catch ( CatchParameter ) Block
  1. Return ContainsDuplicateLabels of Block with argument labelSet.
 FunctionStatementList : [empty]
  1. Return false.
 ModuleItemList : ModuleItemList ModuleItem
  1. Let hasDuplicates be ContainsDuplicateLabels of ModuleItemList with argument labelSet.
  2. If hasDuplicates is true, return true.
  3. Return ContainsDuplicateLabels of ModuleItem with argument labelSet.
 ModuleItem : ImportDeclaration ExportDeclaration
  1. Return false.

8.2.2 Static Semantics: ContainsUndefinedBreakTarget

With parameter labelSet.

Statement : VariableStatement EmptyStatement ExpressionStatement ContinueStatement ReturnStatement ThrowStatement DebuggerStatement Block : { } StatementListItem : Declaration
  1. Return false.
 StatementList : StatementList StatementListItem
  1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of StatementList with argument labelSet.
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedBreakTarget of StatementListItem with argument labelSet.
 IfStatement : if ( Expression ) Statement else Statement
  1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of the first Statement with argument labelSet.
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedBreakTarget of the second Statement with argument labelSet.
 IfStatement : if ( Expression ) Statement
  1. Return ContainsUndefinedBreakTarget of Statement with argument labelSet.
 DoWhileStatement : do Statement while ( Expression ) ;
  1. Return ContainsUndefinedBreakTarget of Statement with argument labelSet.
 WhileStatement : while ( Expression ) Statement
  1. Return ContainsUndefinedBreakTarget of Statement with argument labelSet.
 ForStatement : for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
  1. Return ContainsUndefinedBreakTarget of Statement with argument labelSet.
 ForInOfStatement : for ( LeftHandSideExpression in Expression ) Statement for ( var ForBinding in Expression ) Statement for ( ForDeclaration in Expression ) Statement for ( LeftHandSideExpression of AssignmentExpression ) Statement for ( var ForBinding of AssignmentExpression ) Statement for ( ForDeclaration of AssignmentExpression ) Statement for await ( LeftHandSideExpression of AssignmentExpression ) Statement for await ( var ForBinding of AssignmentExpression ) Statement for await ( ForDeclaration of AssignmentExpression ) Statement
  1. Return ContainsUndefinedBreakTarget of Statement with argument labelSet.
 Note

This section is extended by Annex B.3.6.

 BreakStatement : break ;
  1. Return false.
 BreakStatement : break LabelIdentifier ;
  1. If the StringValue of LabelIdentifier is not an element of labelSet, return true.
  2. Return false.
 WithStatement : with ( Expression ) Statement
  1. Return ContainsUndefinedBreakTarget of Statement with argument labelSet.
 SwitchStatement : switch ( Expression ) CaseBlock
  1. Return ContainsUndefinedBreakTarget of CaseBlock with argument labelSet.
 CaseBlock : { }
  1. Return false.
 CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
  1. If the first CaseClauses is present, then
    1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of the first CaseClauses with argument labelSet.
    2. If hasUndefinedLabels is true, return true.
  2. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of DefaultClause with argument labelSet.
  3. If hasUndefinedLabels is true, return true.
  4. If the second CaseClauses is not present, return false.
  5. Return ContainsUndefinedBreakTarget of the second CaseClauses with argument labelSet.
 CaseClauses : CaseClauses CaseClause
  1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of CaseClauses with argument labelSet.
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedBreakTarget of CaseClause with argument labelSet.
 CaseClause : case Expression : StatementListopt
  1. If the StatementList is present, return ContainsUndefinedBreakTarget of StatementList with argument labelSet.
  2. Return false.
 DefaultClause : default : StatementListopt
  1. If the StatementList is present, return ContainsUndefinedBreakTarget of StatementList with argument labelSet.
  2. Return false.
 LabelledStatement : LabelIdentifier : LabelledItem
  1. Let label be the StringValue of LabelIdentifier.
  2. Let newLabelSet be a copy of labelSet with label appended.
  3. Return ContainsUndefinedBreakTarget of LabelledItem with argument newLabelSet.
 LabelledItem : FunctionDeclaration
  1. Return false.
 TryStatement : try Block Catch
  1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of Block with argument labelSet.
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedBreakTarget of Catch with argument labelSet.
 TryStatement : try Block Finally
  1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of Block with argument labelSet.
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedBreakTarget of Finally with argument labelSet.
 TryStatement : try Block Catch Finally
  1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of Block with argument labelSet.
  2. If hasUndefinedLabels is true, return true.
  3. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of Catch with argument labelSet.
  4. If hasUndefinedLabels is true, return true.
  5. Return ContainsUndefinedBreakTarget of Finally with argument labelSet.
 Catch : catch ( CatchParameter ) Block
  1. Return ContainsUndefinedBreakTarget of Block with argument labelSet.
 FunctionStatementList : [empty]
  1. Return false.
 ModuleItemList : ModuleItemList ModuleItem
  1. Let hasUndefinedLabels be ContainsUndefinedBreakTarget of ModuleItemList with argument labelSet.
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedBreakTarget of ModuleItem with argument labelSet.
 ModuleItem : ImportDeclaration ExportDeclaration
  1. Return false.

8.2.3 Static Semantics: ContainsUndefinedContinueTarget

With parameters iterationSet and labelSet.

Statement : VariableStatement EmptyStatement ExpressionStatement BreakStatement ReturnStatement ThrowStatement DebuggerStatement Block : { } StatementListItem : Declaration
  1. Return false.
 BreakableStatement : IterationStatement
  1. Let newIterationSet be a copy of iterationSet with all the elements of labelSet appended.
  2. Return ContainsUndefinedContinueTarget of IterationStatement with arguments newIterationSet and « ».
 StatementList : StatementList StatementListItem
  1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of StatementList with arguments iterationSet and « ».
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedContinueTarget of StatementListItem with arguments iterationSet and « ».
 IfStatement : if ( Expression ) Statement else Statement
  1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of the first Statement with arguments iterationSet and « ».
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedContinueTarget of the second Statement with arguments iterationSet and « ».
 IfStatement : if ( Expression ) Statement
  1. Return ContainsUndefinedContinueTarget of Statement with arguments iterationSet and « ».
 DoWhileStatement : do Statement while ( Expression ) ;
  1. Return ContainsUndefinedContinueTarget of Statement with arguments iterationSet and « ».
 WhileStatement : while ( Expression ) Statement
  1. Return ContainsUndefinedContinueTarget of Statement with arguments iterationSet and « ».
 ForStatement : for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
  1. Return ContainsUndefinedContinueTarget of Statement with arguments iterationSet and « ».
 ForInOfStatement : for ( LeftHandSideExpression in Expression ) Statement for ( var ForBinding in Expression ) Statement for ( ForDeclaration in Expression ) Statement for ( LeftHandSideExpression of AssignmentExpression ) Statement for ( var ForBinding of AssignmentExpression ) Statement for ( ForDeclaration of AssignmentExpression ) Statement for await ( LeftHandSideExpression of AssignmentExpression ) Statement for await ( var ForBinding of AssignmentExpression ) Statement for await ( ForDeclaration of AssignmentExpression ) Statement
  1. Return ContainsUndefinedContinueTarget of Statement with arguments iterationSet and « ».
 Note

This section is extended by Annex B.3.6.

 ContinueStatement : continue ;
  1. Return false.
 ContinueStatement : continue LabelIdentifier ;
  1. If the StringValue of LabelIdentifier is not an element of iterationSet, return true.
  2. Return false.
 WithStatement : with ( Expression ) Statement
  1. Return ContainsUndefinedContinueTarget of Statement with arguments iterationSet and « ».
 SwitchStatement : switch ( Expression ) CaseBlock
  1. Return ContainsUndefinedContinueTarget of CaseBlock with arguments iterationSet and « ».
 CaseBlock : { }
  1. Return false.
 CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
  1. If the first CaseClauses is present, then
    1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of the first CaseClauses with arguments iterationSet and « ».
    2. If hasUndefinedLabels is true, return true.
  2. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of DefaultClause with arguments iterationSet and « ».
  3. If hasUndefinedLabels is true, return true.
  4. If the second CaseClauses is not present, return false.
  5. Return ContainsUndefinedContinueTarget of the second CaseClauses with arguments iterationSet and « ».
 CaseClauses : CaseClauses CaseClause
  1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of CaseClauses with arguments iterationSet and « ».
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedContinueTarget of CaseClause with arguments iterationSet and « ».
 CaseClause : case Expression : StatementListopt
  1. If the StatementList is present, return ContainsUndefinedContinueTarget of StatementList with arguments iterationSet and « ».
  2. Return false.
 DefaultClause : default : StatementListopt
  1. If the StatementList is present, return ContainsUndefinedContinueTarget of StatementList with arguments iterationSet and « ».
  2. Return false.
 LabelledStatement : LabelIdentifier : LabelledItem
  1. Let label be the StringValue of LabelIdentifier.
  2. Let newLabelSet be a copy of labelSet with label appended.
  3. Return ContainsUndefinedContinueTarget of LabelledItem with arguments iterationSet and newLabelSet.
 LabelledItem : FunctionDeclaration
  1. Return false.
 TryStatement : try Block Catch
  1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of Block with arguments iterationSet and « ».
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedContinueTarget of Catch with arguments iterationSet and « ».
 TryStatement : try Block Finally
  1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of Block with arguments iterationSet and « ».
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedContinueTarget of Finally with arguments iterationSet and « ».
 TryStatement : try Block Catch Finally
  1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of Block with arguments iterationSet and « ».
  2. If hasUndefinedLabels is true, return true.
  3. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of Catch with arguments iterationSet and « ».
  4. If hasUndefinedLabels is true, return true.
  5. Return ContainsUndefinedContinueTarget of Finally with arguments iterationSet and « ».
 Catch : catch ( CatchParameter ) Block
  1. Return ContainsUndefinedContinueTarget of Block with arguments iterationSet and « ».
 FunctionStatementList : [empty]
  1. Return false.
 ModuleItemList : ModuleItemList ModuleItem
  1. Let hasUndefinedLabels be ContainsUndefinedContinueTarget of ModuleItemList with arguments iterationSet and « ».
  2. If hasUndefinedLabels is true, return true.
  3. Return ContainsUndefinedContinueTarget of ModuleItem with arguments iterationSet and « ».
 ModuleItem : ImportDeclaration ExportDeclaration
  1. Return false.