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type-guards

类型守卫与窄化​

ToC​

  • 内置守卫：typeof/instanceof/in
  • 自定义守卫与断言函数
  • satisfies 与 const 断言

内置守卫​

function f(x: unknown) {
  if (typeof x === 'string') { x.toUpperCase() }
  if (x instanceof Date) { x.getTime() }
  if ('id' in (x as any)) { /* ... */ }
}

自定义守卫与断言函数​

function isUser(x: any): x is { id: string } { return x && typeof x.id === 'string' }
function assertNonNull<T>(x: T): asserts x is NonNullable<T> { if (x == null) throw new Error('nullish') }

satisfies 与 const 断言（TS 4.9+）​

const cfg = { port: 8080 } as const satisfies { port: number };