typescript提供一些工具类型来进行类型转换。这些工具类型都是全局的。
1、Partial<T>
将构造类型T的所有属性设置为可选。
//内部实现原理
type Partial<T> = {
[K in keyof T]?: T[K]
}
interface Todo {
id: string;
title: string;
description?: number;
}
type TodoParial = Partial<Todo>;
//等价于
type PersonParial = {
id?: string;
title?: string;
description?: number;
}
//使用场景
function updateTodo(todo: Todo, fieldsToUpdate: Partial<Todo>){
return {...todo, ...fieldsToUpdate};
}
const todo1 = {
title: 'test',
description: 'test xxxx',
};
const todo2 = updateTodo(todo1, {
description: 'test yyy',
});
2、Require<T>
将类型T所有属性设为require
type Require<T> = {
[P in keyof T]-?: T[P];
}
interface Todo {
id: string;
title: string;
description?: number;
}
type TodoRequire = Require<Todo>;
//等价于
type TodoRequire = {
id: string;
title: string;
description: number;
}
3、 Record<K, T>
构造一个类型,其属性名为K,属性值为T
//内部实现原理
type Record<K extends keyof any, T> = {
[P in K]: T;
}
interface PageInfo {
title: string;
}
type Page = 'home' | 'about' | 'contact';
type PageRecord = Record<Page, PageInfo>;
//等价于
type PageRecord = {
home: {
title: string;
};
about: {
title: string;
}
contact: {
title: string;
};
}
//使用场景
const page:Record<Page, PageInfo> = {
home: {title: '首页'},
about: {title: '关于'},
contact: {title: '联系我们'},
}
4、Pick<T, K>
从类型T中挑选部分属性K来构造新的类型
//内部实现原理
type Pick<T, K extends keyof T> = {
[P in K]: T[P];
}
interface Todo {
title: string;
description?: string;
completed: boolean;
}
type TodoPreview = Pick<Todo, 'title' | 'completed'>;
//等价于
type TodoPreview = {
title: string;
completed: boolean;
}
//使用场景
const todoPreview: TodoPreview = {
title: 'test',
completed: false,
}
5、Exclude<T, U>
从类型T中,剔除所有能赋值给U的属性
//内部实现原理
type Exclude<T, U> = T extends U ? never : T;
type T1 = Exclude< 'a' | 'b' | 'c', 'b'| 'c'>;
//等价于
type T1 = 'a'
type T2 = Exclude<number | string | (()=>void), Function>;
//等价于
type T2 = string | number;
6、Extract<T, U>
从类型T中提取所有可以赋值给U的类型
//实现原理
type Extract<T, U> = T extends U ? T : never;
type T1 = Extract< 'a' | 'b' | 'c', 'b'| 'c'>;
//等价于
type T1 = 'b' | 'c'
type T2 = Extract<number | string | (()=>void), 'b'| 'c'| Function>;
//等价于
type T2 = ()=> void;
7、Omit<T, K>
从类型T中剔除所有能赋值给K的属性
type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>
interface Todo {
title: string;
description?: string;
completed?: boolean;
}
type T1 = Omit<Todo, 'title'>
//等价于
type T1 = {
description?: string;
completed?: boolean;
}
8、NonNullable
从T中剔除null和undefined
type NonNullable<T> = T extends undefined | null ? never : T;
type T1 = NonNullable<string[] | undefined | null>;
//等价于
type T1 = string[];
9、ReturnType<T>
由函数类型T的返回值类型构造一个类型
//实现原理
type ReturnType<T extends (...arg: any) => any> = T extends (...arg:any) => infer R ? R : any;
infer R 表示待推断的函数返回值。如果T能够赋值给(...arg:any) => infer R
则结果是R,否则是any
type T1 = ReturnType<()=> string>;
//等价于
type T1 = string;
10、Readonly<T>
将T中所有属性设为只读
type Readonly<T> = {
readonly [K in keyof T]: T[K];
}
interface Todo {
title: string;
description?: string;
completed?: boolean;
}
type T1 = Readonly<Todo>;
//等价于
type T1 = {
readonly title: string;
readonly description?: string;
readonly completed?: boolean;
}
参考文章: TypeScript提供一些工具类型