TypeScript由浅到深(上篇)

在TypeScript中，类型系统允许我们以一种安全的方式操作数据。我们可以在编译时而不是运行时发现错误。这是通过在代码中添加类型注解来实现的。

在TypeScript中，有两种主要的类型：基本类型和复合类型。

1. 基本类型：

let isDone: boolean = false;
let count: number = 10;
let name: string = "Hello, World";

2. 复合类型：

let list: number[] = [1, 2, 3];
let dict: { [key: string]: any } = {
    name: "Hello, World",
    age: 25
};

3. 函数类型：

let add = (x: number, y: number): number => {
    return x + y;
};

4. 类类型：

class Person {
    name: string;
    age: number;
 
    constructor(name: string, age: number) {
        this.name = name;
        this.age = age;
    }
 
    greet() {
        return `Hello, my name is ${this.name}`;
    }
}
 
let person: Person = new Person("Hello, World", 25);

5. 接口类型：

interface Person {
    name: string;
    age: number;
}
 
let person: Person = {
    name: "Hello, World",
    age: 25
};

6. 泛型类型：

let identity = <T>(arg: T): T => {
    return arg;
};
 
let result = identity<string>("Hello, World");

7. 类型别名：

type Person = {
    name: string;
    age: number;
};
 
let person: Person = {
    name: "Hello, World",
    age: 25
};

8. 类型断言：

let someValue: any = "Hello, World";
let strLength: number = (<string>someValue).length;
 
let anotherValue: any = "Hello, World";
let strLength: number = (someValue as string).length;

9. 类型保护：

function isNumber(x: any): x is number {
    return typeof x === "number";
}
 
let myValue: number | string = "Hello, World";
 
if (isNumber(myValue)) {
    // 在这个块内, myValue 类型变成了 number
    let numberValue: number = myValue;
}

10. 类型运算符：

type A = "Hello, World";
type B = "Hello, World";
 
type AorB = A | B;  // "Hello, World" | "Hello, World" 类型等同于 "Hello, W