Exclude 是 TypeScript 中内置的工具类型,它用于从一个联合类型中排除掉你不希望包含的类型,生成一个新的类型。这个工具类型在日常开发中非常有用,它能够帮助我们编写类型安全的代码和更好地实现代码复用。
/** * Exclude from T those types that are assignable to U. * typescript/lib/lib.es5.d.ts */ type Exclude<T, U> = T extends U ? never : T; type T0 = Exclude<"a" | "b" | "c", "a" | "b"> // type T0 = "c"
本文我将介绍 Exclude 工具类型的 8 个使用技巧,掌握这些技巧之后,在工作中你就能更好地利用 Exclude 工具类型来满足不同的使用场景。
1.排除指定的基本数据类型
type MyTypes = string | number | boolean; type StringOrNumber = Exclude<MyTypes, boolean>; let uid: StringOrNumber = "semlinker" // Ok uid = 2024 // Ok uid = false // Error // Type 'boolean' is not assignable to type 'StringOrNumber'.
2.排除 string 或 number 类型的子类型
type Status = "success" | "error" | 200 | 500; type StringStatus = Exclude<Status, number>; // type StringStatus = "success" | "error" type NumberStatus = Exclude<Status, string> // type NumberStatus = 200 | 500
3.排除两个联合类型的共有成员
type TaskStatus = "Todo" | "InProgress" | "Done" | "Archived"; type ModuleHandledStatus = "Todo" | "Done" | "OnHold"; type TaskOnlyStatus = Exclude<TaskStatus, ModuleHandledStatus>; // type TaskOnlyStatus = "InProgress" | "Archived"
4.排除含有特定属性的子类型
Animal 联合类型,包含了多种动物的描述对象,我们想从中排除含有 "legs" 属性的子类型。
type Animal = | { type: 'dog', legs: number } | { type: 'cat', legs: number } | { type: 'fish', fins: number }; type AnimalsWithFins = Exclude<Animal, { legs: number }>; const fish: AnimalsWithFins = { type: 'fish', fins: 6 }; // Ok const dog: AnimalsWithFins = { type: 'dog', legs: 4 }; // Error // Type '"dog"' is not assignable to type '"fish"'.
5.排除同个属性不同类型的子类型
除了可以使用 Exclude<Animal, { legs: number }> 来创建 AnimalsWithFins 类型,该类型还可以通过 Exclude<Animal, { type: 'dog' | 'cat' }> 这种方式来创建。
type Animal = | { type: 'dog', legs: number } | { type: 'cat', legs: number } | { type: 'fish', fins: number }; type AnimalsWithFins = Exclude<Animal, { type: 'dog' | 'cat' }>; const fish: AnimalsWithFins = { type: 'fish', fins: 6 }; // Ok const dog: AnimalsWithFins = { type: 'dog', legs: 4 }; // Error // Type '"dog"' is not assignable to type '"fish"'.
6.排除枚举类型的某些成员
利用 Exclude 工具类型可以排除枚举中的某些成员,从而得到一个新的类型。
enum Status { New, InProgress, Done, Cancelled } type ActiveStatus = Exclude<Status, Status.Done | Status.Cancelled>; // type ActiveStatus = Status.New | Status.InProgress
7.排除指定前缀的字符串字面量类型
利用 Exclude 工具类型和模板字面量类型,我们可以实现从字符串字面量联合类型中,排除指定前缀或后缀的字符串字面量。
type LogEvent = | "userLogin" | "userLogout" | "systemException" | "systemCrash" | "performanceLoadTime" | "performanceApiResponse"; type SystemAndPerformanceEvents = Exclude<LogEvent, `user${string}`>; // type SystemAndPerformanceEvents = "systemException" | "systemCrash" | "performanceLoadTime" | "performanceApiResponse"
8.排除不同格式的字符串字面量类型
type LogEvent = | "userLogin" | "userLogout" | "UserLogin" // New | "UserLogout" // New | "systemException" | "systemCrash" | "performanceLoadTime" | "performanceApiResponse"; type SystemAndPerformanceEvents = Exclude<LogEvent, `${"user" | "User"}${string}`>; // type SystemAndPerformanceEvents = "systemException" | "systemCrash" | "performanceLoadTime" | "performanceApiResponse"
原文地址:https://mp.weixin.qq.com/s/0Fq8a13Nq_0iRTNFyZfVRA