Typescript - 使用字符串获取名称的属性，作为泛型类型

Question

I butchered the title, not sure the technical term for what I want to do. Type constraints are a bit mind boggling to me at the moment as I learn them in both F# and Typescript simultaneously.

I have a variable of interface state that holds lists of every type of data needed on the page

interface state{
    clients: clients[]
    appointments: appointments[]
    ...
}

const ApplicationState : state = {...}

I want a generic function that can be used to get a specific client, appointment, whatever by id.

So something that looks like

getData('clients', 2)

I have started by defining a type of allowed properties (if this can be done a better way let me know).

type entity = "clients" | "appointments"

But would I then be able to get the property of ApplicationState ?

So the getData function could look something like this?

const getData = (foo: entity, id: number) => {
    ApplicationState.magicallyGetPropertyByName.filter(entity => entity.id = foo.id)
}

Is this possible while keeping type inference?

Thank you

Answer 1

The main problem here, is that you are not allowed to call filter on a union like this:

type Clients = {
  tag: 'Clients'
  id: number
}

type Appointments = {
  tag: 'Appointments'
  id: number
}

declare const test: Clients[] | Appointments[]

test.filter(elem => elem)

Please see issues/7294 and issues/13097

However, there is a workaround:

type Clients = {
  tag: 'Clients'
  id: number
}

type Appointments = {
  tag: 'Appointments'
  id: number
}

type State = {
  clients: Clients[]
  appointments: Appointments[]
}

type Entity = keyof State;

declare const ApplicationState: State

const withState = <
  S extends Record<string, { id: number }[]>
>(state: S) =>
  <E extends keyof S>(prop: E, id: number) =>
    state[prop].filter(entity => entity.id === id)

const getData = withState(ApplicationState);

getData('clients', 2)

Playground As you might have noticed, I have declared State as a type instead of interface . This is because interfaces are not indexed by the default. If you change it back to interface , withState will cause an error.

In fact, you don't need to know exact types of clients and appointments , you just have to make sure that all of these types have common property id .