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TypeScript Satisfies Config Inference

Constrain config objects with the satisfies operator, keeping literal inference for keys while enforcing the target shape.

TypescriptConfig Management

Code

snippet
type RouteConfig = Record<string, {
  methods: readonly ('GET' | 'POST')[];
  rateLimit?: number;
}>;

const routes = {
  '/healthz': { methods: ['GET'] },
  '/orders': { methods: ['GET', 'POST'], rateLimit: 120 },
  '/admin/purge': { methods: ['POST'], rateLimit: 5 },
} satisfies RouteConfig;

// satisfies 保留字面量推断：键类型是三个具体路径而非 string
type RoutePath = keyof typeof routes;
const critical: RoutePath = '/admin/purge';

// 联合收窄到真实出现的值
type AllowedMethod = (typeof routes)['/orders']['methods'][number];
const m: AllowedMethod = 'POST';

function routeLimit(path: RoutePath): number {
  return routes[path].rateLimit ?? 60;
}

console.log(critical, m, routeLimit('/healthz'), routeLimit('/orders'));

// 对照：类型注解会拓宽字面量，键类型退化为 string
const widened: RouteConfig = {
  '/healthz': { methods: ['GET'] },
};
type WidenedKey = keyof typeof widened; // string
const anyPath: WidenedKey = '/anything-goes';

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