Partial<Type>
构造一个 Type 的所有属性都设置为 optional 的类型。 此实用程序将返回表示给定类型的所有子集的类型。
例子：
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",
});
测试结果：第一个输入参数的 description 字段被第二个参数的同名字段覆盖了。
如果把两个操作数前的 ... 都去掉，则失去了两个对象做交集的效果，变成了求并集。
Required 的效果和 Optional 正好相反：
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>'.
Readonly<Type>
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.
Record<Keys,Type>
构造一个对象类型，其属性键为 Keys，属性值为 Type。 此实用程序可用于将一种类型的属性映射到另一种类型。
例子：
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>
通过从 Type 中选取一组属性键（字符串文字或字符串文字的并集）来构造一个类型。
例子：
interface Todo {
title: string;
description: string;
completed: boolean;
}
type TodoPreview = Pick<Todo, "title" | "completed">;
const todo: TodoPreview = {
title: "Clean room",
completed: false,
};
todo;
新的类型，是从 Todo 类型中把 title 和 completed 属性摘出来。
Omit<Type, Keys>
通过从 Type 中选取所有属性然后删除键（字符串文字或字符串文字的并集）来构造一个类型。
同 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,
};
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
Exclude<Type, ExcludedUnion>
通过从 Type 中排除所有可分配给 ExcludedUnion 的联合成员来构造一个类型。
例子：
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
Extract<Type, Union>
通过从 Type 中提取可分配给 Union 的所有联合成员来构造一个类型。取交集。
type T0 = Extract<"a" | "b" | "c", "a" | "f">;
type T0 = "a"
type T1 = Extract<string | number | (() => void), Function>;
type T1 = () => void
NonNullable<Type>
通过从中排除 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>
根据函数类型 Type 的参数中使用的类型构造元组类型。
例子：
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>
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（或者如果 Type 不是函数，则类型 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]
type T3 = ConstructorParameters<any>;
type T3 = unknown[]
type T4 = 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 T4 = never
ReturnType<Type>
构造一个由函数 Type 的返回类型组成的类型。
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'.
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'.
type T8 = any
InstanceType<Type>
构造一个由 Type 中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
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