I tend to think you should simply coerce to boolean here: `if (!this._exited)`
Comparing explicitly to true / false (even ===) is not generally necessary IMHO.
Moreover, here, as you are testing against false first, that means that if for some reason `this._existed` would be either `null` or `undefined` (think later refactoring), then it would evaluate as true in your code - which is likely not what you want - what you want here is `_existed` to be either "truthy" or "falsy", which is what you get with a simple implicit coerce.
Hope that helps.