LibJS: Throw a TypeError when an arrow function is used as a constructor

Author: https://github.com/jack-karamanian
Commit: https://github.com/SerenityOS/serenity/commit/3ffb0a4e873
Pull-request: https://github.com/SerenityOS/serenity/pull/2454

Libraries/LibJS/Runtime/ScriptFunction.cpp

@@ -125,6 +125,8 @@ Value ScriptFunction::call(Interpreter& interpreter)
 
 Value ScriptFunction::construct(Interpreter& interpreter)
 {
+    if (m_is_arrow_function)
+        return interpreter.throw_exception<TypeError>(String::format("%s is not a constructor", m_name.characters()));
     return call(interpreter);
 }
 

Libraries/LibJS/Tests/arrow-functions.js

@@ -81,6 +81,13 @@ try {
 
     assert(Baz.prototype === undefined);
 
+    assertThrowsError(() => {
+        new Baz();
+    }, {
+        error: TypeError,
+        message: "Baz is not a constructor"
+    });
+
     (() => {
         "use strict";
         assert(isStrictMode());