typescript-fsa + payload mapper

fsa.ts

export interface AnyAction {
    type: any
}

export interface Action<P = any> extends AnyAction {
    type: string
    payload: P
    [key: string]: any
}

export interface ActionCreator<P = any, I = P> {
    (input: I, extra?: object): Action<P>
    type: string
    match: (action: any) => action is Action<P>
    withMapper: <R>(mapper: (input: P) => R) => ActionCreator<R, P>
}

export function createActionFactory(prefix = '') {
    return function actionFactory<P>(type: string) {
        type = prefix + type
        const createAction: any = (input: P, extra?: any): Action => {
            return { type, payload: input, ...extra }
        }

        createAction.type = type
        createAction.match = (action: any) => action != null && action.type === type
        createAction.withMapper = withMapper.bind(null, createAction)
        return createAction as ActionCreator<P>
    }
}

export function withMapper<T, R>(creator: ActionCreator<T>, fn: (input: T) => R) {
    const createAction = (input: T, extra?: any) => {
        const action = creator(input, extra)
        return { ...action, payload: fn(action.payload) }
    }
    return Object.assign(createAction, creator)
}


const createAction = createActionFactory('foo/')

const addTodo = createAction<string>('ADD_TODO')
    .withMapper(content => ({ id: Date.now(), content }))

console.log(addTodo('hello'))