# Avoid `takeUntil` subscription leaks (`no-unsafe-takeuntil`)

This rule effects failures whenever `takeUntil` is used in observable compositions that can leak subscriptions.

Although it's recommended that `takeUntil` be placed last - to ensure unsubscription from any inner observables - there are a number of operators that might _need_ to be placed after it - like `toArray` or any other operator that depends upon a `complete` notification. The rule is aware of these operators (see the rule's options, below) and will not effect failures if they are placed after `takeUntil`.

## Rule details

Examples of **incorrect** code for this rule:

```ts
const combined = source
    .pipe(takeUntil(notifier), combineLatest(b))
    .subscribe((value) => console.log(value));
```

Examples of **correct** code for this rule:

```ts
const combined = source
    .pipe(combineLatest(b), takeUntil(notifier))
    .subscribe((value) => console.log(value));
```

## Options

This rule accepts a single option which is an object with `alias` and `allow` properties. The `alias` property is an array of names of operators that should be treated similarly to `takeUntil` and the `allow` property is an array of names of operators that are safe to use after `takeUntil`.

By default, the `allow` property contains all of the built-in operators that are safe to use after `takeUntil`.

```json
{
    "rxjs/no-unsafe-takeuntil": [
        "error",
        {
            "alias": ["untilDestroyed"]
        }
    ]
}
```

The properties in the options object are themselves optional; they do not all have to be specified.

## Further reading

-   [Avoiding takeUntil leaks](https://ncjamieson.com/avoiding-takeuntil-leaks/)