TypeScript 类的自身类型

需要定义一个 class 类型的非实例变量时，可以用以下格式:

• 变量名 : typeof 类名; class 定义了有参数的构造函数时，不可用
• 变量名 : new() => 类名;
• 变量名 : { new(): 类名 };
  当 class 定义了有参数的构造函数时，也需要对应：
• 变量名 : new(name:string) => 类名;
• 变量名 : { new(name:string): 类名 };

export class Animal { }

export class Dog extends Animal { }

export class Fox extends Animal {

    public constructor(name: string) {
        super();
    }

}

export class Test {

    private _animalType1: { new(): Animal };
    private _animalType2: new () => Animal;
    private _animalType3: typeof Animal;
    private _animalType4: new (name: string) => Animal;
    private _foxType: typeof Fox;

    public constructor() {
        this._animalType1 = Animal;
        this._animalType1 = Dog;
        //this._animalType1 = Fox; // 编译错误：Type 'typeof Fox' is not assignable to type 'new () => Animal'

        this._animalType2 = Animal;
        this._animalType2 = Dog;
        //this._animalType2 = Fox; // 编译错误：Type 'typeof Fox' is not assignable to type 'new () => Animal'

        this._animalType3 = Animal;
        this._animalType3 = Dog;
        //this._animalType3 = Fox; // 编译错误：Type 'typeof Fox' is not assignable to type 'new () => Animal'

        this._animalType4 = Animal;
        this._animalType4 = Dog;
        this._animalType4 = Fox; // 编译通过

        this._foxType = Fox;

        //this.getName1(Fox); // 编译错误：Argument of type 'typeof Fox' is not assignable to parameter of type 'typeof Animal'
        //this.getName2(Fox); // 编译错误：Argument of type 'typeof Fox' is not assignable to parameter of type 'typeof Animal'
        //this.getName3(Fox); // 编译错误：Argument of type 'typeof Fox' is not assignable to parameter of type 'typeof Animal'
        this.getName4(Fox); // 编译通过
        this.getName5(Fox); // 编译通过
        //this.getName6(Fox); // 编译错误：Argument of type 'typeof Fox' is not assignable to parameter of type 'new () => Fox'.
        //this.getName7(Fox); // 编译错误：Argument of type 'typeof Fox' is not assignable to parameter of type 'new () => Fox'
        this.getName8(Fox); // 编译通过
        this.getName9(Fox); // 编译通过
    }

    public getName1(type: { new(): Animal }): string {
        return type.prototype.constructor.name;
    }

    public getName2(type: new () => Animal): string {
        return type.prototype.constructor.name;
    }

    public getName3(type: typeof Animal): string {
        return type.prototype.constructor.name;
    }

    public getName4(type: new (name: string) => Animal): string {
        return type.prototype.constructor.name;
    }

    public getName5(type: { new(name: string): Animal }): string {
        return type.prototype.constructor.name;
    }

    public getName6<T extends Animal>(type: new () => T): string {
        return type.prototype.constructor.name;
    }

    public getName7<T extends Animal>(type: { new(): T }): string {
        return type.prototype.constructor.name;
    }

    public getName8<T extends Animal>(type: new (name: string) => T): string {
        return type.prototype.constructor.name;
    }

    public getName9<T extends Animal>(type: { new(name: string): T }): string {
        return type.prototype.constructor.name;
    }

    // 此方法不可用
    // 编译错误：T' only refers to a type, but is being used as a value here.
    //public getName10<T extends Animal>(type: typeof T): string {
    //    return type.prototype.constructor.name;
    //}

}

参考：
https://typescript.p6p.net/typescript-tutorial/class.html