• It is a Syntax Error if the BoundNames of BindingList contains "let".
• It is a Syntax Error if the BoundNames of BindingList contains any duplicate entries.

• It is a Syntax Error if Initializer is not present and IsConstantDeclaration of the LexicalDeclaration containing this LexicalBinding is true.

With parameters value and environment.

With parameters iteratorRecord and environment.

With parameters value, environment, and propertyName.

• It is a Syntax Error if IsLabelledFunction(Statement) is true.

The abstract operation LoopContinues with arguments completion and labelSet is defined by the following steps:

With parameter labelSet.

With parameter labelSet.

With parameters iterationSet and labelSet.

With parameter labelSet.

With parameter labelSet.

With parameter labelSet.

With parameters iterationSet and labelSet.

With parameter labelSet.

• It is a Syntax Error if any element of the BoundNames of LexicalDeclaration also occurs in the VarDeclaredNames of Statement.

With parameter labelSet.

With parameter labelSet.

With parameters iterationSet and labelSet.

With parameter labelSet.

The abstract operation ForBodyEvaluation with arguments test, increment, stmt, perIterationBindings, and labelSet is performed as follows:

The abstract operation CreatePerIterationEnvironment with argument perIterationBindings is performed as follows:

• It is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.

If LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression can be parsed with no tokens left over using AssignmentPattern as the goal symbol then the following rules are not applied. Instead, the Early Error rules for AssignmentPattern are used.

• It is a Syntax Error if IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.
• It is a Syntax Error if the LeftHandSideExpression is CoverParenthesizedExpressionAndArrowParameterList : ( Expression ) and Expression derives a phrase that would produce a Syntax Error according to these rules if that phrase were substituted for LeftHandSideExpression. This rule is recursively applied.

• It is a Syntax Error if the BoundNames of ForDeclaration contains "let".
• It is a Syntax Error if any element of the BoundNames of ForDeclaration also occurs in the VarDeclaredNames of Statement.
• It is a Syntax Error if the BoundNames of ForDeclaration contains any duplicate entries.

With parameter labelSet.

With parameter labelSet.

With parameters iterationSet and labelSet.

With parameters value and environment.

With parameter environment.

With parameter labelSet.

The abstract operation ForIn/OfHeadEvaluation is called with arguments TDZnames, expr, and iterationKind. The value of iterationKind is either enumerate or iterate.

The abstract operation ForIn/OfBodyEvaluation is called with arguments lhs, stmt, iterator, iterationKind, lhsKind, and labelSet. The value of iterationKind is either enumerate or iterate. The value of lhsKind is either assignment, varBinding or lexicalBinding.

When the abstract operation EnumerateObjectProperties is called with argument O, the following steps are taken:

The iterator's throw and return methods are null and are never invoked. The iterator's next method processes object properties to determine whether the property key should be returned as an iterator value. Returned property keys do not include keys that are Symbols. Properties of the target object may be deleted during enumeration. A property that is deleted before it is processed by the iterator's next method is ignored. If new properties are added to the target object during enumeration, the newly added properties are not guaranteed to be processed in the active enumeration. A property name will be returned by the iterator's next method at most once in any enumeration.

Enumerating the properties of the target object includes enumerating properties of its prototype, and the prototype of the prototype, and so on, recursively; but a property of a prototype is not processed if it has the same name as a property that has already been processed by the iterator's next method. The values of [[Enumerable]] attributes are not considered when determining if a property of a prototype object has already been processed. The enumerable property names of prototype objects must be obtained by invoking EnumerateObjectProperties passing the prototype object as the argument. EnumerateObjectProperties must obtain the own property keys of the target object by calling its [[OwnPropertyKeys]] internal method. Property attributes of the target object must be obtained by calling its [[GetOwnProperty]] internal method.

            function* EnumerateObjectProperties(obj) {
              const visited = new Set();
              for (const key of Reflect.ownKeys(obj)) {
                if (typeof key === "symbol") continue;
                const desc = Reflect.getOwnPropertyDescriptor(obj, key);
                if (desc && !visited.has(key)) {
                  visited.add(key);
                  if (desc.enumerable) yield key;
                }
              }
              const proto = Reflect.getPrototypeOf(obj);
              if (proto === null) return;
              for (const protoKey of EnumerateObjectProperties(proto)) {
                if (!visited.has(protoKey)) yield protoKey;
              }
            }