javascript - TS 自动推导的问题?

Question

在 hook 里我想根据是否存入 transformData 函数，自动推导出返回的 tableData 的类型，现在的问题是，当我传入 transformData 时，tableData 的类型是 (T | R)[] , 如果我不传 transformData, tableData 的类型是 (T|(R 的默认值))[] , 如何才能在传入transformData时 tableData 得到 R[], 不传时, tableData 得到 T[] ?

import { GetListFn, PaginationProps, Query } from '@/types/globe'import { sleep } from 'radash'type SetMode = 'reset' | 'append'export default function useTable<    T extends Record<string, any> = Record<string, any>,    Q extends Record<string, any> | undefined = undefined,    R extends Record<string, any> = Record<string, any>>(config: {    request: (params: Query<Q>) => Promise<CommonResponse<{ records: T[], total: number }>>    search?: Q    getListOnMounted?: boolean    setMode?: SetMode    transformData?: (data: T[]) => R[]}) {    type InferItem<T, F> = F extends undefined ? T : R    const { request, search = {}, getListOnMounted = true, setMode = 'reset', transformData } = config    ...    const tableData = ref([]) as Ref<InferItem<T, typeof transformData>[]>    const getList = async (config?: { mode: SetMode }) => {        ...        try {            loading.value = true            const { ok, data } = await request(query)            await sleep(100)            if (ok) {                const responseData = data.data.records || []                if (responseData.length) {                    const maybeTransformData = transformData?.(responseData) ?? responseData                    tableData.value =                        _mode === 'reset' ? maybeTransformData : [...tableData.value, ...maybeTransformData]                } else if (_mode === 'reset') {                    tableData.value = []                }                pagination.total = data.data.total ?? 0                noMoreData.value = !responseData.length || tableData.value.length === pagination.total            }        } finally {            loading.value = false        }    }        ...    return {        ...        tableData,        ...    }}

这是我的使用方式

const { tableData } = useTable({    request: (params) => receptionist.list(Number(route.params.id), params),    search: { keyword: '' },    transformData: (data) => data.map((v) => ({ label: v.receptName, value: v.id }))})

求助各位大佬

Answer 1

declare function f<T extends [] | [number]>(...args: T): T extends [] ? 1 : 2const a = f()  // 1const b = f(123)  // 2