Analyzing different kinds of inputs received by a function

Let's say we have the following abstractions for fetching data from an API:

  • Data storage class

    class DataItem<T> {
    data?: T | null
}

  • Query function

    function queryData (
    fn: () => Promise<any>
    item: DataItem<any>
    transformResponse?: (value: any) => any // value - result from fn
)

We intend to use these as shown below:

const item = new DataItem<ItemDto>()

async function request (): Promise<ItemDto> { ... }

queryData(
    () => request()
    item
)

Is there a way to achieve the following without using generic queryData function:

  1. Validate that the output of function fn aligns with the type stored in item?
  2. If we provide a function transformResponse, can its return value be checked against the type of item?
  3. If we pass a function transformResponse, is it possible to ensure that its parameter value matches the type returned by function fn?
typescript

Answer №1

Yes, using a generic type variable is the perfect solution for achieving this. You can make use of the following code snippet to fulfill your requirements:

function fetchData<T>(
  fetchFunc: () => Promise<T>,
  item: DataItem<T>,
  processResponse: (response: Promise<T>) => DataItem<T>
)

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