ts小记（一）

[coolpail]

any

any是最高也是最低

1. any可以分配给任何类型

let a: any;
let b: number = a;

2. 任何类型可以分配any

let a: any = 123

unknow

任何类型可以分配给unknow；当有类型防护时，能缩小类型范围
[..] unknown是任何类型安全的对应物。任何事物都可以分配给未知对象，但是未知事物不能分配给任何事物，只有它本身以及没有类型声明或基于控制流的缩小。同样，在未先声明或缩小为更具体的类型之前，不允许对未知数执行任何操作。

let a: unknown = 123;
declare const maybe: unknown;
if (maybe === true) {
  // TypeScript knows that maybe is a boolean now
  const aBoolean: boolean = maybe;
  // So, it cannot be a string
  const aString: string = maybe;
}

readonly number[]

1. number[] 可以分配给 readonly number[]；反过来就不行

解决多余属性检查

1. 创建新变量作为函数入参，但需要有共同的某一个或多个属性
2. 类型断言as
3. 修改interface定义，增加[propName: string]: unknown

用接口来描述函数

1. 只需要函数的入参类型和返回值类型一致就行，不需要参数一样

interface fn {
    (s: string, b: string): boolean
}
const f: fn = (a, b) => true

类实现接口

1. 必须实现接口的方法和属性

interface ClockInterface {
  currentTime: Date;
  setTime(d: Date): void;
}

class Clock implements ClockInterface {
  currentTime: Date = new Date();
  setTime(d: Date) {
    this.currentTime = d;
  }
  constructor(h: number, m: number) {} //这个构造函数没有强制绑定类型
}

类实现接口只实现实例属性，不是实现静态属性，所以下面例子报错

interface ClockConstructor {
  new (hour: number, minute: number): void;
}

class Clock implements ClockConstructor {
//Class 'Clock' incorrectly implements interface 'ClockConstructor'.
  //Type 'Clock' provides no match for the signature 'new (hour: number, minute: number): any'.
  currentTime: Date;
  constructor(h: number, m: number) {}
}

定义构造函数以及类的实现

interface ClockConstructor {
  new (hour: number, minute: number): ClockInterface;
}

interface ClockInterface {
  tick(): void;
}

const Clock: ClockConstructor = class Clock implements ClockInterface {
  constructor(h: number, m: number) {}
  tick() {
    console.log("beep beep");
  }
};

扩展接口(接口实现接口)

interface Shape {
  color: string;
}

interface PenStroke {
  penWidth: number;
}

interface Square extends Shape, PenStroke {
  sideLength: number;
}

let square = {} as Square;
square.color = "blue";
square.sideLength = 10;
square.penWidth = 5.0;

接口扩展类

class Control {
  private state: any;
}
// 接口实现了继承了类，并拥有了私有属性state
interface SelectableControl extends Control {
  select(): void;
}
// 因为Button继承了Control,也就继承了私有属性state，所以可以实现SelectableControl
class Button extends Control implements SelectableControl {
  select() {}
}

class TextBox extends Control {
  select() {}
}
//因为Button不拥有私有属性state，所以不可以实现SelectableControl
class ImageControl implements SelectableControl {
// Class 'ImageControl' incorrectly implements interface 'SelectableControl'.
  // Types have separate declarations of a private property 'state'.
  private state: any;
  select() {}
}