Not able to understand debounce parameters in rxjs

Question

I wanted to understand the intellisense displayed in the visual code which got me more confused

debounce(
durationSelector: (value: {}) => SubscribableOrPromise<any>
): MonoTypeOperatorFunction<{}>

from the above example, I think I understood the following:

1. debounce is the name of the function

2. durationSelector is a function which that a single parameter:

   a. value which takes Object as parameter

   b. SubscribableOrPromise<any> is the type that the function is going to return

3. MonoTypeOperatorFunction<{}>, not able to understand how a function can return MonoTypeOperatorFunction<{}> when it already returns SubscribableOrPromise<any>, this is where I am confused and not able to understand

Answer 1

not able to understand how a function can return MonoTypeOperatorFunction<{}> when it already returns SubscribableOrPromise<any>

That's not what is being described here, you don't have one function that returns MonoTypeOperatorFunction and also SubscribableOrPromise. You have two functions:

1. debounce; and
2. the durationSelector argument to debounce (which may be anonymous in your code).

debounce returns MonoTypeOperatorFunction<{}>, so the result can be passed to pipe (which takes OperatorFunctions, of which that's a subtype).

debounce requires the function as you're passing as an argument to it to return SubscribableOrPromise<any>, the line:

(value: {}) => SubscribableOrPromise<any>

is the declaration of the argument, durationSelector; it's a function type.

I'd recommend reading up on "higher-order functions", as that's a really important concept to understand if you're going to use RxJS.