TypeScript高級類型-內置實用工具類型
預備知識
Partial<T>
將泛型 T 中的所有屬性轉化爲可選屬性
/**
* Make all properties in T optional
*/
type Partial<T> = {
[P in keyof T]?: T[P];
};
interface IUser {
name: string;
age: number;
}
type t = Partial<IUser>;
/* type t = {
name?: string;
age?: number
} */
Required<T>
將泛型 T 中的所有屬性轉化爲必選屬性
/**
* Make all properties in T required
*/
type Required<T> = {
[P in keyof T]-?: T[P];
};
interface IUser {
name?: string;
age?: number;
}
type t = Required<IUser>;
/* type t = {
name: string;
age: number
} */
Readonly<T>
將泛型 T 中的所有屬性轉化爲只讀屬性
/**
* Make all properties in T readonly
*/
type Readonly<T> = {
readonly [P in keyof T]: T[P];
};
interface IUser {
name: string;
age: number;
}
type t = Readonly<IUser>;
/* type t = {
readonly name: string;
readonly age: number
} */
Pick<T, K extends keyof T>
從泛型 T 中檢出指定的屬性並組成一個新的對象類型
/**
* From T, pick a set of properties whose keys are in the union K
*/
type Pick<T, K extends keyof T> = {
[P in K]: T[P];
};
interface IUser {
name: string;
age: number;
address: string;
}
type t = Pick<IUser, 'name' | 'age'>;
/* type t = {
name: string;
age: number
} */
Record<K extends keyof any, T>
Record 允許從 Union 類型中創建新類型，Union 類型中的值用作新類型的屬性。
經常用於接口 response 類型聲明
/**
* Construct a type with a set of properties K of type T
*/
type Record<K extends keyof any, T> = {
[P in K]: T;
};
type Car = 'Audi' | 'BMW' | 'MercedesBenz'
type CarList = Record<Car, {age: number}>
const cars: CarList = {
Audi: { age: 119 },
BMW: { age: 113 },
MercedesBenz: { age: 133 },
}
Exclude<T, U>
從泛型 T 中排除可以賦值給泛型 U 的類型
/**
* Exclude from T those types that are assignable to U
*/
type Exclude<T, U> = T extends U ? never : T;
type a = 1 | 2 | 3;
type t = Exclude<a, 1 | 2>;
/* type t = 3 */
Extract<T, U>
從泛型 T 中提取可以賦值給泛型 U 的類型
/**
* Extract from T those types that are assignable to U
*/
type Extract<T, U> = T extends U ? T : never;
type a = 1 | 2 | 3;
type t = Extract<a, 1 | 2>;
/* type t = 1 | 2 */
Omit<T, K extends keyof any>
從泛型 T 中提取出不在泛型 K 中的屬性類型，並組成一個新的對象類型
/**
* Construct a type with the properties of T except for those in type K.
*/
type Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;
interface IUser {
name: string;
age: number;
address: string;
}
type t = Omit<IUser, 'name' | 'age'>;
/* type t = {
address: string;
} */
NonNullable<T>
從泛型 T 中排除掉 null 和 undefined
/**
* Exclude null and undefined from T
*/
type NonNullable<T> = T extends null | undefined ? never : T;
type t = NonNullable<'name' | undefined | null>;
/* type t = 'name' */
Parameters<T extends (...args: any) => any>
以元組的方式獲得函數的入參類型
/**
* Obtain the parameters of a function type in a tuple
*/
type Parameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? P : never;
type t = Parameters<(name: string) => any>; // type t = [string]
type t2 = Parameters<((name: string) => any) | ((age: number) => any)>; // type t2 = [string] | [number]
ConstructorParameters<T extends new (...args: any) => any>
以元組的方式獲得構造函數的入參類型
/**
* Obtain the parameters of a constructor function type in a tuple
*/
type ConstructorParameters<T extends new (...args: any) => any> = T extends new (...args: infer P) => any ? P : never;
type t = ConstructorParameters<(new (name: string) => any) | (new (age: number) => any)>;
// type t = [string] | [number]
ReturnType<T extends (...args: any) => any>
獲得函數返回值的類型
/**
* Obtain the return type of a function type
*/
type ReturnType<T extends (...args: any) => any> = T extends (...args: any) => infer R ? R : any;
type t = ReturnType<(name: string) => string | number>
// type t = string | number
InstanceType<T extends new (...args: any) => any>
獲得構造函數返回值的類型
/**
* Obtain the return type of a constructor function type
*/
type InstanceType<T extends new (...args: any) => any> = T extends new (...args: any) => infer R ? R : any;
type t = InstanceType<new (name: string) => {name: string, age: number}>
/*
type h = {
name: string;
age: number;
}
*/
總結
- 重點理解這些內置的工具類型的定義
- 能夠以此爲”引“寫一些工具類型並運用到項目中去