Bugs in negated `instanceof` expressions
gorosgobe opened this issue · comments
in and instanceof expressions in JS
a in obj;
a instanceof C;can be negated by grouping them and applying the ! operator, i.e.
!(a in obj);
!(a instanceof C);Applying the ! operator incorrectly (on the LHS operand) leads to bugs:
!a in obj; // will evaluate to false, unless obj has a "true" or "false" key
!a instanceof C; // will evaluate to false, unless C overrides instanceof with a @@hasInstance methodFor more information, please see these MDN docs and the no-unsafe-negation recommended Eslint rule.
I have found a potentially problematic instance of the above bugs in your codebase:
Line 2263 in 9d5df48