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LibJS: Implicitly break for..in loop if the RHS result is nullish

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This implements the missing step 6a of 14.7.5.6 ForIn/OfHeadEvaluation:

    a. If exprValue is undefined or null, then
        i. Return Completion { [[Type]]: break, [[Value]]: empty, [[Target]]: empty }.

In other words, this should just do nothing instead of throwing during
the undefined to object coercion:

    for (const x in undefined);
This commit is contained in:
Linus Groh 2021-04-10 18:47:18 +02:00 • committed by Andreas Kling
parent 9cd010167a
commit 2172e51246
2 changed files with 8 additions and 0 deletions
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2
Userland/Libraries/LibJS/AST.cpp
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@ -477,6 +477,8 @@ Value ForInStatement::execute(Interpreter& interpreter, GlobalObject& global_obj
auto rhs_result = m_rhs->execute(interpreter, global_object);
if (interpreter.exception())
return {};
if (rhs_result.is_nullish())
return {};
auto* object = rhs_result.to_object(global_object);
while (object) {
auto property_names = object->get_enumerable_own_property_names(Object::PropertyKind::Key);