typescript 如何把字面量数组转为联合类型声明?

Question

如果这个字面量数组没有指定类型的话是可以的：

const routes = [
  { path: '/test' }
] as const

type paths = typeof routes[number]['path']

但是如果routes指定了类型（为了书写的时候有语法提示），就不行，paths会推断成string类型：

const routes: RouteRecordRaw[] = [
  { path: '/test' }
] as const

type paths = typeof routes[number]['path']

有什么解决方法吗

解决方法

import type { RouteRecordRaw } from 'vue-router'

type Route<T> = Omit<RouteRecordRaw, 'path'> & { path: T }

function defineRoutes<T extends string>(routes: Route<T>[]) {
  return routes
}

const routes = defineRoutes([
  {
    path: '/contract/index'
  }
])

type paths = typeof routes[number]['path']

Answer 1

改成泛型，用个函数包一下

interface RouteRecordRaw<T extends string> {
  path: T
}

function defineRoutes<T extends string>(routes: RouteRecordRaw<T>[]) {
  return routes
}

const routes = defineRoutes([
  { path: '/test' },
  { path: '/foo' },
])

type paths = typeof routes[number]['path']

Answer 2

还有一个笨方法，就是用 satisfies 关键字，这个关键字的作用是判断是否符合一个类型并给出类型提示，但其原类型还是你定义的那个类型，可以和 as const 一起用。

Answer 3

interface RouteRecordRaw {
    path: string
}

const _routes = [
    { path: '/test' }
] as const

const routes: readonly RouteRecordRaw[] = _routes

type paths = typeof _routes[number]['path']