guard-for-in

Require for-in loops to include an if statement.

Looping over objects with a for-in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

Invalid:

for (const key in obj) { foo(obj, key); } 

Valid:

for (const key in obj) { if (Object.hasOwn(obj, key)) { foo(obj, key); } } 

for (const key in obj) { if (!Object.hasOwn(obj, key)) { continue; } foo(obj, key); }