Typescript的装饰器

装饰器（Decorator）模式 的定义：指在不改变现有对象结构的情况下，动态地给该对象增加一些职责（即增加其额外功能）的模式，它属于对象结构型模式。

函数装饰器

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function sayGood(sayThing: ()=> void): (msg: string)=>void{
  return function (msg: string){
    console.log('say good' + msg);
    sayThing();
  }
}

sayGood(()=>{console.log('hello boy')})('candy');

类装饰器

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function age(target: Function) {
  target.prototype.sayName = function() {
    console.log("hello jonny");
  };
}

@age
class Login {
  public username: string = "";
  public password: string = "";
}

const login: any = new Login();
login.sayName(); //"hello jonny"
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function setAge(param: string) {
  return function(target: any) {
    target.prototype.sayName = function() {
      console.log(param);
    };
  };
}

@setAge("Hello Candy!")
class Login {
  public username: string = "";
  public password: string = "";
}

const login: any = new Login();
login.sayName();  //'hello candy'

属性装饰器

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function hName(param: string) {
  return function(target: any, propertyName: string) {
    target[propertyName] = param;
  };
}

class Hello {
  @hName("Jonny")
  name: string;
}

console.log(new Hello().name); // 输出: Jonny

方法装饰器

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function GET(url: string) {
  return function(target, methodName: string, descriptor: PropertyDescriptor) {
    target.run = function() {
      console.log("ok");
      descriptor.value();
    };
  };
}

class HelloService {
  constructor() {}
  @GET("xx")
  getUser() {
    console.log("no");
  }
}

const instance: any = new HelloService();

instance.run();  //ok,no

参数装饰器

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function PathParam(paramName: string) {
  return function(target, methodName: string, paramIndex: number) {
    !target.$Meta && (target.$Meta = {});
    target.$Meta[paramIndex] = paramName;
  };
}

class HelloService {
  constructor() {}
  getUser(@PathParam("userId") userId: string) {}
}

console.log((<any>HelloService).prototype.$Meta); // {'0':'userId'}