What is the syntax for defining a generic type in TypeScript when using the property name "type"?

Is there a way to declare a generic type GetAppActions where if T is equal to trigger, only the trigger data property is displayed, and vice versa?

type GetAppActionType = 'trigger' | 'action'
interface AppActionInputField {}

type GetAppActions<T = GetAppActionType> = {
    data: {
        action: { inputFields: AppActionInputField[] }
        trigger: { inputFields: AppActionInputField[] }
    }
    type: T
}

Answer №1

You have the option to implement a mapped type

interface AppActionInputField {}

type GetAppActions<T extends "trigger"|"action"> = {
    data: {
        [K in T]: { inputFields: AppActionInputField[] }
    },
    type: T
}

const sample: GetAppActions<"trigger"> = {
    data: {
        trigger: { inputFields: [{}] }
    },
    type: "trigger"
}

Link to Playground

Answer №2

If you want to restrict the data property based on the type, you can utilize discriminating union. It essentially acts like a switch statement for your types.


interface AppActionInputField { }

type AppActions = {
  type: "trigger"
  data: {
    trigger: { inputFields: AppActionInputField[] }
  }
} | {
  type: "action",
  data: {
    action: { inputFields: AppActionInputField[] }
  }
}

type ActionType = AppActions["type"];
// "actions" | "trigger"

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