typescript类型深入

ts类型深入

new(…args: any[]) => T

import "reflect-metadata";

const Service = (): ClassDecorator => {
    return target => {
        // [ [Function: Bar], [Function: String] ]
        console.log(Reflect.getMetadata('design:paramtypes', target));
    };
};

class Bar { }

@Service()
class Foo {
    constructor(bar: Bar, baz: string) { }
}

// 相当于创建一个匿名类，然后new出一个对象a。
let a = new class {
    hello() {
        console.log('ddd');
    }
}

a.hello();

tsc 编译后。

var Bar = /** @class */ (function () {
    function Bar() {
    }
    return Bar;
}());
var Foo = /** @class */ (function () {
    function Foo(bar, baz) {
    }
    Foo = __decorate([
        Service(),
        __metadata("design:paramtypes", [Bar, String])
    ], Foo);
    return Foo;
}());
var a = new /** @class */ (function () {
    function class_1() {
    }
    class_1.prototype.hello = function () {
        console.log('ddd');
    };
    return class_1;
}());
a.hello();

类的类型。

this is a class named class

class Person {}

let p = new Peson()

p的类型是Person

Person的类型是 new(…args: any[]) => Person

class Person {
    walk() {
        console.log('walk');
    }
}

// 定义一个类型。
interface Type<T> {
    new(...args: any[]): T;
}

let b = new class {
    hello<T>(target: Type<any>): T {
        console.log(target); // [Function: Person]
        return new target();
    }
}
let c = b.hello<Person>(Person);
c.walk();

let d: Type<Person> = Person;
console.log(d) // [Function: Person]
console.log(Person) // [Function: Person]
console.log(new Person()) // Person {}



// 定义一个类型
export type GenericClassDecorator<T> = (target: T) => void;

const Service1 = (): GenericClassDecorator<Type<any>> => {
    return (target: Type<any>) => {
        // do something with `target`, e.g. some kind of validation or passing it to the Injector and store them
    };
};