TypeScript装饰器与反射元数据实例详解

function Sealed(constructor: Function) {
    Object.seal(constructor);
    Object.seal(constructor.prototype);
}
@Sealed
class Greeter {
    constructor(public greeting: string) {}
    greet() {
        return "Hello, " + this.greeting;
    }
}

function Log(target: Object, propertyKey: string, descriptor: TypedPropertyDescriptor<any>) {
    let originalMethod = descriptor.value; // 保存原始函数
    descriptor.value = function (...args: any[]) {
        console.log("Arguments: ", JSON.stringify(args));
        let result = originalMethod.apply(this, args);
 console.log("Result: ", result);
        return result;
    }
}
class Calculator {
    @Log
    add(x: number, y: number): number {
        return x + y;
    }
}

function ReadOnly(target: any, key: string, descriptor: PropertyDescriptor) {
    descriptor.writable = false;
    return descriptor;
}
class Circle {
    private _radius: number;
    constructor(radius: number) {
        this._radius = radius;
    }
    @ReadOnly
    get radius() {
        return this._radius;
    }
}

npm install reflect-metadata --save

import "reflect-metadata";

{
  "compilerOptions": {
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "target": "ES5",
    "module": "commonjs"
  }
}

function logType(target : any, key : string) {
  var t = Reflect.getMetadata("design:type", target, key);
  console.log(`${key} type: ${t.name}`);
}
class Demo{ 
  @logType
  public attr1 : string;
}