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LibJS: Add short circuit logical evaluation

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When evaluating logical binop expressions, the rhs must not be
evaluated if the lhs leads to the whole expression not being
truthy.
This commit is contained in:
Stephan Unverwerth 2020-04-03 19:11:31 +02:00 • committed by Andreas Kling
commit 520311eb8b
Notes: sideshowbarker 2024-07-19 07:58:32 +09:00
2 changed files with 28 additions and 4 deletions
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17
Libraries/LibJS/AST.cpp
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@ -282,17 +282,26 @@ Value LogicalExpression::execute(Interpreter& interpreter) const
auto lhs_result = m_lhs->execute(interpreter);
if (interpreter.exception())
return {};
auto rhs_result = m_rhs->execute(interpreter);
if (interpreter.exception())
return {};
switch (m_op) {
case LogicalOp::And:
if (lhs_result.to_boolean())
if (lhs_result.to_boolean()) {
auto rhs_result = m_rhs->execute(interpreter);
if (interpreter.exception())
return {};
return Value(rhs_result);
}
return Value(lhs_result);
case LogicalOp::Or:
if (lhs_result.to_boolean())
return Value(lhs_result);
auto rhs_result = m_rhs->execute(interpreter);
if (interpreter.exception())
return {};
return Value(rhs_result);
}

15
Libraries/LibJS/Tests/logical-expressions-short-circuit.js Normal file
View file

@ -0,0 +1,15 @@
function assert(x) { if (!x) throw 1; }
try {
let foo = 1;
false && (foo = 2);
assert(foo === 1);
foo = 1;
true || (foo = 2);
assert(foo === 1);
console.log("PASS");
} catch (e) {
console.log("FAIL: " + e);
}