Question

当我们想要替换构造函数时，我试图理解类装饰器如何在Typescript中工作。我见过这个演示：

const log = <T>(originalConstructor: new(...args: any[]) => T) => {
    function newConstructor(... args) {
        console.log("Arguments: ", args.join(", "));
        new originalConstructor(args);
    }
    newConstructor.prototype = originalConstructor.prototype;
    return newConstructor;
}

@log
class Pet {
    constructor(name: string, age: number) {}
}

new Pet("Azor", 12);
//Arguments: Azor, 12

一切都被理解，但这一行：

newConstructor.prototype = originalConstructor.prototype;

为什么我们这样做？

Answer 1

类如：

class Pet {
    constructor(name: string, age: number) {}
    dosomething() {
        console.log("Something...");
    }
}

在定位ES5时编译成函数：

var Pet = (function () {
    function Pet(name, age) {
    }
    Pet.prototype.dosomething = function () {
        console.log("Something...");
    };
    return Pet;
}());

当我们使用函数来定义类时，你会发现。这些方法被添加到函数的原型中。

这意味着如果要创建新的构造函数（新函数），则需要从旧对象复制所有方法（原型）：

function logClass(target: any) {

  // save a reference to the original constructor
  const original = target;

  // a utility function to generate instances of a class
  function construct(constructor: any, args: any[]) {
    const c: any = function () {
      return constructor.apply(this, args);
    };
    c.prototype = constructor.prototype;
    return new c();
  }

  // the new constructor behaviour
  const newConstructor: any = function (...args: any[]) {
    console.log("New: " + original.name);
    return construct(original, args);
  };

  // copy prototype so intanceof operator still works
  newConstructor.prototype = original.prototype;

  // return new constructor (will override original)
  return newConstructor;
}

您可以在"Decorators & metadata reflection in TypeScript: From Novice to Expert (Part I)"

了解详情

更新

请参阅https://github.com/remojansen/LearningTypeScript/tree/master/chapters/chapter_08了解更新版本。

Typescript中的类装饰器

1 个答案:

更新