14.7.1.1 LoopContinues ( completion, labelSet )

The abstract operation LoopContinues takes arguments completion and labelSet. It performs the following steps when called:

14.7.1.2 Runtime Semantics: LoopEvaluation

With parameter labelSet.

14.7.2.1 Static Semantics: Early Errors

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

14.7.2.2 Runtime Semantics: DoWhileLoopEvaluation

With parameter labelSet.

14.7.3.1 Static Semantics: Early Errors

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

14.7.3.2 Runtime Semantics: WhileLoopEvaluation

With parameter labelSet.

14.7.4.1 Static Semantics: Early Errors

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

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

14.7.4.2 Runtime Semantics: ForLoopEvaluation

With parameter labelSet.

14.7.4.3 ForBodyEvaluation ( test, increment, stmt, perIterationBindings, labelSet )

The abstract operation ForBodyEvaluation takes arguments test, increment, stmt, perIterationBindings, and labelSet. It performs the following steps when called:

14.7.4.4 CreatePerIterationEnvironment ( perIterationBindings )

The abstract operation CreatePerIterationEnvironment takes argument perIterationBindings. It performs the following steps when called:

14.7.5.1 Static Semantics: Early Errors

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

If LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral, the following Early Error rules are applied:

• It is a Syntax Error if LeftHandSideExpression is not covering an AssignmentPattern.
• All Early Error rules for AssignmentPattern and its derived productions also apply to the AssignmentPattern that is covered by LeftHandSideExpression.

If LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral, the following Early Error rule is applied:

• It is a Syntax Error if AssignmentTargetType of LeftHandSideExpression is not simple.

• 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.

14.7.5.2 Static Semantics: IsDestructuring

14.7.5.3 Runtime Semantics: ForDeclarationBindingInitialization

With parameters value and environment.

14.7.5.4 Runtime Semantics: ForDeclarationBindingInstantiation

With parameter environment.

14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation

With parameter labelSet.

14.7.5.6 ForIn/OfHeadEvaluation ( uninitializedBoundNames, expr, iterationKind )

The abstract operation ForIn/OfHeadEvaluation takes arguments uninitializedBoundNames, expr, and iterationKind (either enumerate, iterate, or async-iterate). It performs the following steps when called:

14.7.5.7 ForIn/OfBodyEvaluation ( lhs, stmt, iteratorRecord, iterationKind, lhsKind, labelSet [ , iteratorKind ] )

The abstract operation ForIn/OfBodyEvaluation takes arguments lhs, stmt, iteratorRecord, iterationKind, lhsKind (either assignment, varBinding or lexicalBinding), and labelSet and optional argument iteratorKind (either sync or async). It performs the following steps when called:

14.7.5.8 Runtime Semantics: Evaluation

14.7.5.9 EnumerateObjectProperties ( O )

The abstract operation EnumerateObjectProperties takes argument O. It performs the following steps when called:

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.

In addition, if neither O nor any object in its prototype chain is a Proxy exotic object, Integer-Indexed exotic object, module namespace exotic object, or implementation provided exotic object, then the iterator must behave as would the iterator given by CreateForInIterator(O) until one of the following occurs:

• the value of the [[Prototype]] internal slot of O or an object in its prototype chain changes,
• a property is removed from O or an object in its prototype chain,
• a property is added to an object in O's prototype chain, or
• the value of the [[Enumerable]] attribute of a property of O or an object in its prototype chain changes.

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.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;
  }
}

14.7.5.10 For-In Iterator Objects

A For-In Iterator is an object that represents a specific iteration over some specific object. For-In Iterator objects are never directly accessible to ECMAScript code; they exist solely to illustrate the behaviour of EnumerateObjectProperties.