LibJS: Throw in strict mode when assigning property to primitive value

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/8ff4587f653
Pull-request: https://github.com/SerenityOS/serenity/pull/2429

Libraries/LibJS/AST.cpp

@@ -559,15 +559,12 @@ Reference Identifier::to_reference(Interpreter& interpreter) const
 Reference MemberExpression::to_reference(Interpreter& interpreter) const
 {
     auto object_value = m_object->execute(interpreter);
-    if (object_value.is_empty())
-        return {};
-    auto* object = object_value.to_object(interpreter);
-    if (!object)
+    if (interpreter.exception())
         return {};
     auto property_name = computed_property_name(interpreter);
     if (!property_name.is_valid())
         return {};
-    return { object, property_name };
+    return { object_value, property_name };
 }
 
 Value UnaryExpression::execute(Interpreter& interpreter) const

Libraries/LibJS/Runtime/Reference.cpp

@@ -50,6 +50,11 @@ void Reference::put(Interpreter& interpreter, Value value)
         return;
     }
 
+    if (!base().is_object() && interpreter.in_strict_mode()) {
+        interpreter.throw_exception<TypeError>(String::format("Can't assign property %s to primitive value", m_name.to_string().characters()));
+        return;
+    }
+
     auto* object = base().to_object(interpreter);
     if (!object)
         return;

Libraries/LibJS/Tests/strict-mode-errors.js

@@ -0,0 +1,18 @@
+"use strict";
+
+load("test-common.js")
+
+try {
+    [true, false, "foo", 123].forEach(primitive => {
+        assertThrowsError(() => {
+            primitive.foo = "bar";
+        }, {
+            error: TypeError,
+            message: "Can't assign property foo to primitive value"
+        });
+    });
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}