ts 定义类型

1. Parameters 类型工具用于提取函数的参数类型，并将其转换为一个元组类型

function add(a: number, b: number): number {
return a + b;
}
type AddParameters = Parameters<typeof add>;

// 定义一个变量，其类型为 AddParameters
const params: AddParameters = [1, 2];

// 使用提取的参数类型调用函数
const result = add(...params); // 3
console.log(result); // 输出: 3

2.枚举类型

enum Color { Red, Green, Blue }
let c: Color = Color.Green;
console.log(c); // 输出: 1

3.Unknown 类型，必须先检查

let value: unknown;
value = 42;
value = "Hello";

if (typeof value === "string") {
console.log(value.toUpperCase()); // 安全地调用字符串方法
}

4.类型别名

type Point = {
x: number;
y: number;
};

let point: Point = { x: 1, y: 2 };

5.泛型

function identity<T>(arg: T): T {
return arg;
}

let output = identity<string>("myString");
console.log(output); // 输出: "myString"

6.联合类型

let value: string | number;
value = "hello";
value = 10;

7.交叉类型

type Person = {
name: string;
};

type Loggable = {
log: () => void;
};

type PersonWithLogging = Person & Loggable;

let person: PersonWithLogging = {
name: "Alice",
log() {
console.log(`Name: ${this.name}`);
},
};

8.类型断言

let someValue: any = "this is a string";

let strLength: number = (someValue as string).length;

9.条件类型

type IsNumber<T> = T extends number ? "Yes" : "No";

type IsNumberResult1 = IsNumber<42>; // "Yes"
type IsNumberResult2 = IsNumber<string>; // "No"

8.Partial 类型，可选
type PartialPerson = Partial<Person>;

10.只读类型  

interface Person {
name: string;
age: number;
address: string;
}

type ReadonlyPerson = Readonly<Person>;
// { readonly name: string; readonly age: number; readonly address: string; }

11.排除 Omit<T, K>

interface Person {
name: string;
age: number;
address: string;
}

type PersonWithoutAge = Omit<Person, 'age'>;
// { name: string; address: string; }

12.选择类型，返回新类型 Pick<T, K>

interface Person {
name: string;
age: number;
address: string;
}

type PersonNameAndAge = Pick<Person, 'name' | 'age'>;
// { name: string; age: number; }