I am looking to enhance the capabilities of the rxjs5 Observable class by adding a static function. While this can be easily accomplished in plain JavaScript:
var myStaticFn = function() { /* ... */ };
Observable.myStaticFn = myStaticFn;
this approach works, but it becomes a bit trickier in TypeScript as I cannot directly access Observable.myStaticFn since the property myStaticFn is not recognized on the Observable class.
How can I declare/extend the rxjs5 Module Observable class so that I can use my added function in a safe and typed manner?
Note: As an example, below is a demonstration of extending a non-static function to the Observable (for instance, creating a custom rxjs Operator), which functions perfectly, though it's not what I intend to achieve!
function myOperator(this: Observable<any>): Observable<any> = function(){ /*...*/ };
Observable.prototype.myOperator = myOperator;
declare module "rxjs/Observable" {
interface Observable<T> {
myOperator: typeof myOperator;
}
}
The provided solution works due to TypeScript's ability to treat the Observable as an interface using the `declare` syntax, allowing for augmentation/merging of interfaces. However, there isn't a direct way in TypeScript to define a static function within an interface.
Furthermore, it is impractical to inherit from the Observable class, such as creating a new class like ExtendedObservable, as every user would then have to utilize this new type throughout the project instead of the standard Observable type. This concept also falls short when attempting to include different static methods on the Observable based on imported modules.