Typescript 工具类型

Typescript 工具类型

TypeScript 目前提供了 18 种工具类型以及 4 种内置字符串操作工具类型来促进常见的类型转换。这些工具在全局作用域内可用。在 node_modules/typescript/lib/lib.es5.d.ts 文件中。

Awaited<Type> 4.5

此类型旨在对 async 函数中的 await 或 Promise 中的 .then() 方法等操作进行建模 - 具体来说，他们递归地解开 Promise 并获取返回的类型。

示例

type A = Awaited<Promise<string>>; // type A = string
 
type B = Awaited<Promise<Promise<number>>>; // type B = number
 
type C = Awaited<boolean | Promise<number>>; // type C = number | boolean

Partial<Type> 2.1

Partial 部分的

构造一个将 Type 的所有属性设置为可选的类型。此工具将返回一个表示给定类型的所有子集可选的类型。

示例

interface Todo {
  title: string;
  description: string;
}
 
function updateTodo(todo: Todo, fieldsToUpdate: Partial<Todo>) {
  return { ...todo, ...fieldsToUpdate };
}
 
const todo1 = {
  title: "organize desk",
  description: "clear clutter",
};
 
const todo2 = updateTodo(todo1, {
  description: "throw out trash",
});

Required<Type> 2.8

构造一个由设置为 required 的 Type 的所有属性组成的类型。与 Partial 相反。

原理用的就是映射修饰符的前缀，通过添加前缀 - 或 + 来移除或添加这些修饰符。如果你不添加前缀，则假定为 +。

示例

interface Props {
  a?: number;
  b?: string;
}
 
const obj: Props = { a: 5 };
 
const obj2: Required<Props> = { a: 5 };
// Property 'b' is missing in type '{ a: number; }' but required in type 'Required<Props>'.

Record<Keys, Type> 2.1

Record 记录

构造一个对象类型，其属性键为 Keys，其属性值为 Type。此工具可用于将一种类型的属性映射到另一种类型。

interface CatInfo {
  age: number;
  breed: string;
}
 
type CatName = "miffy" | "boris" | "mordred";
 
const cats: Record<CatName, CatInfo> = {
  miffy: { age: 10, breed: "Persian" },
  boris: { age: 5, breed: "Maine Coon" },
  mordred: { age: 16, breed: "British Shorthair" },
};
 
cats.boris; // const cats: Record<CatName, CatInfo>

Pick<Type, Keys> 2.1

Pick 选择

通过从 Type 中选取一组属性 Keys（字符串字面或字符串字面的并集）来构造一个类型。

示例

interface Todo {
  title: string;
  description: string;
  completed: boolean;
}
 
type TodoPreview = Pick<Todo, "title" | "completed">;
 
const todo: TodoPreview = {
  title: "Clean room",
  completed: false,
};

Omit<Type, Keys> 3.5

Omit 省略

通过从 Type 中选择所有属性然后删除 Keys（字符串字面或字符串字面的并集）来构造一个类型。与 Pick 相反。

interface Todo {
  title: string;
  description: string;
  completed: boolean;
  createdAt: number;
}
 
type TodoPreview = Omit<Todo, "description">;
const todo: TodoPreview = {
  title: "Clean room",
  completed: false,
  createdAt: 1615544252770,
};
 
type TodoInfo = Omit<Todo, "completed" | "createdAt">;
const todoInfo: TodoInfo = {
  title: "Pick up kids",
  description: "Kindergarten closes at 5pm",
};
 

Exclude<UnionType, ExcludedMembers> 2.8

通过从 UnionType 联合类型中排除所有可分配给 ExcludedMembers 的联合成员来构造一个类型。

注意与 Omit<Type, Keys> 的区别，Omit 是对 Type 的剔除，Exclude 是对 UnionType 的剔除。

示例

type T0 = Exclude<"a" | "b" | "c", "a">;
     // type T0 = "b" | "c"
     
type T1 = Exclude<"a" | "b" | "c", "a" | "b">;
     // type T1 = "c"
     
type T2 = Exclude<string | number | (() => void), Function>;
     // type T2 = string | number
 
type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; x: number }
  | { kind: "triangle"; x: number; y: number };
type T3 = Exclude<Shape, { kind: "circle" }>
    // type T3 = {
	//     kind: "square";
	//     x: number;
	// } | {
	//     kind: "triangle";
	//     x: number;
	//     y: number;
	// }

Extract<Type, Union> 2.8

Extract 摘录

通过从 Type 中提取所有可分配给 Union 的联合成员来构造一个类型。

type T0 = Extract<"a" | "b" | "c", "a" | "f">;
     // type T0 = "a"
     
type T1 = Extract<string | number | (() => void), Function>;
     // type T1 = () => void
 
type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; x: number }
  | { kind: "triangle"; x: number; y: number };
type T2 = Extract<Shape, { kind: "circle" }>  
	// type T2 = {
	//     kind: "circle";
	//     radius: number;
	// }

NonNullable<Type> 2.8

通过从 Type 中排除 null 和 undefined 来构造一个类型。

type T0 = NonNullable<string | number | undefined>;
     // type T0 = string | number
type T1 = NonNullable<string[] | null | undefined>;
     // type T1 = string[]

Parameters<Type> 3.1

从函数类型 Type 的参数中使用的类型构造元组类型。（如果 Type 不是函数，则生成类型 never）。

declare function f1(arg: { a: number; b: string }): void;
 
type T0 = Parameters<() => string>;
     // type T0 = []
     
type T1 = Parameters<(s: string) => void>;
     // type T1 = [s: string]
     
type T2 = Parameters<<T>(arg: T) => T>;
     // type T2 = [arg: unknown]
     
type T3 = Parameters<typeof f1>;
	// type T3 = [arg: {
	//     a: number;
	//     b: string;
	// }]
	
type T4 = Parameters<any>;
     // type T4 = unknown[]
     
type T5 = Parameters<never>;
     // type T5 = never
     
type T6 = Parameters<string>;
	// Type 'string' does not satisfy the constraint '(...args: any) => any'.
     // type T6 = never
     
type T7 = Parameters<Function>;
	// Type 'Function' does not satisfy the constraint '(...args: any) => any'.
    // Type 'Function' provides no match for the signature '(...args: any): any'.
    // type T7 = never

ConstructorParameters<Type> 3.1

从构造函数类型的类型构造元组或数组类型。它生成一个包含所有参数类型的元组类型（如果 Type 不是函数，则生成类型 never）。

type T0 = ConstructorParameters<ErrorConstructor>;
     // type T0 = [message?: string]
     
type T1 = ConstructorParameters<FunctionConstructor>;
     // type T1 = string[]
     
type T2 = ConstructorParameters<RegExpConstructor>;
     // type T2 = [pattern: string | RegExp, flags?: string]

class C {
  constructor(a: number, b: string) {}
}
type T3 = ConstructorParameters<typeof C>;
     // type T3 = [a: number, b: string]
     
type T4 = ConstructorParameters<any>;
     // type T4 = unknown[]
 
type T5 = ConstructorParameters<Function>;
	// Type 'Function' does not satisfy the constraint 'abstract new (...args: any) => any'.
  // Type 'Function' provides no match for the signature 'new (...args: any): any'.
  // type T5 = never

ReturnType<Type> 2.8

ReturnType 接受一个函数类型 Type 并产生它的返回类型。

❗❗❗注意接收参数应为函数类型❗❗❗是函数类型。返回的是函数类型的返回类型。

对于重载函数，这将是最后一个签名的返回类型；见【在条件类型中推断】。

示例

declare function f1(): { a: number; b: string };
 
type T0 = ReturnType<() => string>; // type T0 = string

type T1 = ReturnType<(s: string) => void>; // type T1 = void

type T2 = ReturnType<<T>() => T>; // type T2 = unknown

type T3 = ReturnType<<T extends U, U extends number[]>() => T>; // type T3 = number[]

type T4 = ReturnType<typeof f1>;  
// type T4 = {
//    a: number;
//    b: string;
// }

type T5 = ReturnType<any>; // type T5 = any

type T6 = ReturnType<never>; // type T6 = never

type T7 = ReturnType<string>; // type T7 = any
// Type 'string' does not satisfy the constraint '(...args: any) => any'.
// string 不符合 ReturnType 参数的约束，应该为一个有返回类型的函数 (...args: any) => any
     

type T8 = ReturnType<Function>; // type T8 = any
// Type 'Function' does not satisfy the constraint '(...args: any) => any'.
// Type 'Function' provides no match for the signature '(...args: any): any'.

InstanceType<Type> 2.8

构造一个由 Type 中的构造函数的实例类型组成的类型。

class C {
  x = 0;
  y = 0;
}
type T0 = InstanceType<typeof C>;
     // type T0 = C
     
type T1 = InstanceType<any>;
     // type T1 = any
     
type T2 = InstanceType<never>;
     // type T2 = never
     
type T3 = InstanceType<string>;
	 // Type 'string' does not satisfy the constraint 'abstract new (...args: any) => any'.
     // type T3 = any
     
type T4 = InstanceType<Function>;
	 // Type 'Function' does not satisfy the constraint 'abstract new (...args: any) => any'.
  	 // Type 'Function' provides no match for the signature 'new (...args: any): any'.
     // type T4 = any

NoInfer<Type> 5.4

阻止对所包含类型的推断。除了阻止推断之外，NoInfer 与 Type 相同。

function createStreetLight<C extends string>(
  colors: C[],
  defaultColor?: NoInfer<C>,
) {
  // ...
}
createStreetLight(["red", "yellow", "green"], "red");  // OK
createStreetLight(["red", "yellow", "green"], "blue");  // Error

ThisParameterType<Type> 3.3

提取函数类型的 this 参数的类型，如果函数类型没有 this 参数，则提取 unknown。

function toHex(this: Number) {
  return this.toString(16);
}
 
function numberToString(n: ThisParameterType<typeof toHex>) {
  return toHex.apply(n);
}

OmitThisParameter<Type> 3.3

从 Type 中删除 this 参数。如果 Type 没有显式声明的 this 参数，则结果只是 Type。否则，将从 Type 创建一个没有 this 参数的新函数类型。泛型被删除，只有最后一个重载签名被传播到新的函数类型中。

function toHex(this: Number) {
  return this.toString(16);
}
 
const fiveToHex: OmitThisParameter<typeof toHex> = toHex.bind(5);
 
console.log(fiveToHex());

ThisType<Type> 2.3

此工具不返回转换后的类型。相反，它用作上下文 this 类型的标记。请注意，必须启用 noImplicitThis 标志才能使用此工具。

type ObjectDescriptor<D, M> = {
  data?: D;
  methods?: M & ThisType<D & M>; // Type of 'this' in methods is D & M
};
 
function makeObject<D, M>(desc: ObjectDescriptor<D, M>): D & M {
  let data: object = desc.data || {};
  let methods: object = desc.methods || {};
  return { ...data, ...methods } as D & M;
}
 
let obj = makeObject({
  data: { x: 0, y: 0 },
  methods: {
    moveBy(dx: number, dy: number) {
      this.x += dx; // Strongly typed this
      this.y += dy; // Strongly typed this
    },
  },
});
 
obj.x = 10;
obj.y = 20;
obj.moveBy(5, 5);

内在字符串操作类型

Uppercase

将字符串中的每个字符转换为大写版本。

示例

type Greeting = "Hello, world"
type ShoutyGreeting = Uppercase<Greeting>
           // type ShoutyGreeting = "HELLO, WORLD"
 
type ASCIICacheKey<Str extends string> = `ID-${Uppercase<Str>}`
type MainID = ASCIICacheKey<"my_app">
       // type MainID = "ID-MY_APP"

Lowercase

将字符串中的每个字符转换为等效的小写字母。

type Greeting = "Hello, world"
type QuietGreeting = Lowercase<Greeting>
          
type QuietGreeting = "hello, world"
 
type ASCIICacheKey<Str extends string> = `id-${Lowercase<Str>}`
type MainID = ASCIICacheKey<"MY_APP">
       
type MainID = "id-my_app"

Capitalize

将字符串中的第一个字符转换为等效的大写字母。

type LowercaseGreeting = "hello, world";
type Greeting = Capitalize<LowercaseGreeting>;
        
type Greeting = "Hello, world"

Uncapitalize

将字符串中的第一个字符转换为等效的小写字母。

type UppercaseGreeting = "HELLO WORLD";
type UncomfortableGreeting = Uncapitalize<UppercaseGreeting>;
              
type UncomfortableGreeting = "hELLO WORLD"