Question

打字稿：2.4.1

我试图创建一个辅助函数来生成redux动作创建器。

我得到了什么：

interface IAction<T extends string, P = undefined> {
    type: T;
    payload: P;
}

function createAction<T extends string>(type: T): () => IAction<T, undefined>;
function createAction<T extends string = '', U = undefined, V = {}>(type: T, actionCreator: (payload: U) => V): (payload: U) => IAction<T, V>;
function createAction<T extends string>(type: T, actionCreator?: (payload?: any) => any) {
    return (payload: any) => ({
        payload,
        type,
    });
}

enum ActionType {
    INCREMENT = 'COUNTER/INCREMENT',
    DECREMENT = 'COUNTER/DECREMENT',
    ASYNC_INCREMENT = 'COUNTER/ASYNC_INCREMENT',
}

const increment = createAction(ActionType.INCREMENT, () => ({ amount: 1 }));
const incrementBy = createAction(ActionType.INCREMENT, (amount: number) => amount);

在这个例子中，我希望increment是一个带0个参数的函数，而incrementBy则取1（a number）。

incrementBy按预期工作，但在调用increment()（没有参数）时，Typescript会抛出此错误：

[ts] Expected 1 arguments, but got 0;

尝试以与我致电incrementBy相同的方式拨打电话，例如increment(42)，我收到此错误：

[ts] Argument of type '42' is not assignable to parameter of type 'undefined';

这有效：increment(undefined)。

有没有办法解决这个问题？

Answer 1

你应该简单地创建另一个重载，它表示它将返回一个没有参数的函数，而不是一个以undefined为唯一参数的函数。

function createAction<T extends string>(type: T): () => IAction<T, undefined>;
function createAction<T extends string, V>(type: T, actionCreator: () => V): () => IAction<T, V>;
function createAction<T extends string, U, V>(type: T, actionCreator: (payload: U) => V): (payload: U) => IAction<T, V>;
function createAction<T extends string, U, V>(type: T, actionCreator?: (payload: U) => V): (payload: U) => IAction<T, V> {
    return (payload: any) => ({
        payload,
        type,
    });
}

但是，您的实现似乎对传递的函数没有任何作用。你可能想这样做：

function createAction<T extends string>(type: T): () => IAction<T, undefined>;
function createAction<T extends string, V>(type: T, actionCreator: () => V): () => IAction<T, V>;
function createAction<T extends string, U, V>(type: T, actionCreator: (payload: U) => V): (payload: U) => IAction<T, V>;
function createAction<T extends string, U, V>(type: T, actionCreator?: (payload: U) => V): (payload: U) => IAction<T, V> {
    if (actionCreator) {
        return (payload: U) => ({
            payload: actionCreator(payload),
            type,
        });
    } else {
        return () => ({
            payload: undefined,
            type
        });
    }
}

Typescript期望undefined作为参数

1 个答案: