实用类型

TypeScript 提供了一些实用类型来简化常见的类型转换。这些实用类型在全局范围内可用。

Awaited<Type>

发布: 4.5

此类型旨在模拟 async 函数中的 await 或 Promise 上的 .then() 方法的操作 - 特别是它们递归解开 Promise 的方式。

示例
ts
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
Try

Partial<Type>

已发布
2.1

构造一个类型，其中 Type 的所有属性都设置为可选。此实用程序将返回一个表示给定类型所有子集的类型。

示例
ts
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",
});
Try

Required<Type>

已发布
2.8

构造一个类型，其中 Type 的所有属性都设置为必需。与 Partial 相反。

示例
ts
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>'.2741Property 'b' is missing in type '{ a: number; }' but required in type 'Required<Props>'.Try

Readonly<Type>

已发布
2.1

构造一个类型，其中 Type 的所有属性都设置为 readonly，这意味着构造类型的属性不能重新赋值。

示例
ts
interface Todo {
  title: string;
}
 
const todo: Readonly<Todo> = {
  title: "Delete inactive users",
};
 
todo.title = "Hello";
Cannot assign to 'title' because it is a read-only property.2540Cannot assign to 'title' because it is a read-only property.Try

此实用程序对于表示在运行时将失败的赋值表达式很有用（即当尝试重新分配 冻结对象 的属性时）。

Object.freeze
ts
function freeze<Type>(obj: Type): Readonly<Type>;

Record<Keys, Type>

已发布
2.1

构建一个对象类型，其属性键为 Keys，属性值为 Type。此实用程序可用于将类型的属性映射到另一个类型。

示例
ts
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>
Try

Pick<Type, Keys>

已发布
2.1

通过从 Type 中选取属性集 Keys（字符串字面量或字符串字面量的联合）来构建类型。

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

Omit<Type, Keys>

已发布
3.5

通过从Type中选取所有属性，然后移除Keys（字符串字面量或字符串字面量联合）来构建一个类型。与Pick相反。

示例
ts
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,
};
 
todo;
 
const todo: TodoPreview
 
type TodoInfo = Omit<Todo, "completed" | "createdAt">;
 
const todoInfo: TodoInfo = {
  title: "Pick up kids",
  description: "Kindergarten closes at 5pm",
};
 
todoInfo;
   
const todoInfo: TodoInfo
Try

Exclude<UnionType, ExcludedMembers>

已发布
2.8

通过从UnionType中排除所有可分配给ExcludedMembers的联合成员来构建一个类型。

示例
ts
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;
}
Try

Extract<Type, Union>

已发布
2.8

通过从Type中提取所有可分配给Union的联合成员来构建一个类型。

示例
ts
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;
}
Try

NonNullable<Type>

已发布
2.8

从 Type 中排除 null 和 undefined，构造一个类型。

示例
ts
type T0 = NonNullable<string | number | undefined>;
     
type T0 = string | number
type T1 = NonNullable<string[] | null | undefined>;
     
type T1 = string[]
Try

Parameters<Type>

已发布
3.1

从函数类型 Type 的参数中使用的类型构造一个元组类型。

对于重载函数，这将是最后一个签名的参数；请参阅 条件类型中的推断。

示例
ts
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'.2344Type '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'.2344Type 'Function' does not satisfy the constraint '(...args: any) => any'.
  Type 'Function' provides no match for the signature '(...args: any): any'.
     
type T7 = never
Try

ConstructorParameters<Type>

已发布
3.1

从构造函数类型中类型的类型构造一个元组或数组类型。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，则为 never 类型）。

示例
ts
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'.2344Type '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
Try

ReturnType<Type>

已发布
2.8

构造一个由函数 Type 的返回类型组成的类型。

对于重载函数，这将是最后一个签名的返回类型；请参阅 条件类型中的推断。

示例
ts
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 'string' does not satisfy the constraint '(...args: any) => any'.2344Type 'string' does not satisfy the constraint '(...args: any) => any'.
     
type T7 = any
type T8 = ReturnType<Function>;
Type 'Function' does not satisfy the constraint '(...args: any) => any'.
  Type 'Function' provides no match for the signature '(...args: any): any'.2344Type 'Function' does not satisfy the constraint '(...args: any) => any'.
  Type 'Function' provides no match for the signature '(...args: any): any'.
     
type T8 = any
Try

InstanceType<Type>

已发布
2.8

构造一个由 Type 中的构造函数的实例类型组成的类型。

示例
ts
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'.2344Type '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'.2344Type '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
Try

ThisParameterType<Type>

已发布
3.3

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

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

OmitThisParameter<Type>

已发布
3.3

从 Type 中移除 this 参数。如果 Type 没有显式声明 this 参数，则结果就是 Type 本身。否则，将从 Type 创建一个没有 this 参数的新函数类型。泛型会被擦除，只有最后一个重载签名会被传播到新的函数类型中。

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

ThisType<Type>

已发布
2.3

此实用程序不会返回转换后的类型。相反，它充当上下文 this 类型的标记。请注意，必须启用 noImplicitThis 标志才能使用此实用程序。

示例
ts
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);
Try

在上面的示例中，makeObject 参数中的 methods 对象具有包含 ThisType<D & M> 的上下文类型，因此 methods 对象中方法内的 this 的类型为 { x: number, y: number } & { moveBy(dx: number, dy: number): void }。请注意，methods 属性的类型同时是推断目标和方法中 this 类型的来源。

ThisType<T> 标记接口只是一个在 lib.d.ts 中声明的空接口。除了在对象字面量的上下文类型中被识别之外，该接口的行为与任何空接口一样。

内在字符串操作类型

Uppercase<StringType>

Lowercase<StringType>

Capitalize<StringType>

Uncapitalize<StringType>

为了帮助处理模板字符串字面量周围的字符串操作，TypeScript 包含了一组类型，这些类型可以在类型系统中用于字符串操作。您可以在 模板字面量类型 文档中找到它们。

TypeScript 文档是一个开源项目。您可以通过 发送 Pull Request ❤ 来帮助我们改进这些页面。

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最后更新时间：2024 年 3 月 21 日