如何在可构造的JavaScript对象上为属性创建陷阱

问题描述

代理具有trap for new operator，从理论上讲，该代理应允许我们创建将构造函数自变量传递到目标对象的代理。其工作方式示例如下：

function monster1(disposition) {
  this.disposition = disposition;
}

const handler1 = {
  construct(target,args) {
    console.log('monster1 constructor called');
    // expected output: "monster1 constructor called"

    return new target(...args);
  },get(...args) {
    console.info('get trap triggered!')
  }
};

const proxy1 = new Proxy(monster1,handler1);

const instance = new proxy1('fierce')

console.log(instance.disposition);
// expected output: "fierce"

console.log(instance.unkNownProp);
// expected output: "get trap triggered!" <-- doesn't happen

这很好用。除了instance.unkNownProp现在不再触发get陷阱之外。我现在如何拦截属性？

解决方法

在Construct内，您有return new target(...args);。这样会创建一个没有设置代理的新JS对象。

您应该在新创建的对象上设置一个附加代理，以拦截在那里的属性访问。

赞：

function monster1(disposition) {
  this.disposition = disposition;
}

const handler1 = {
  construct(target,args) {
    console.log('monster1 constructor called');
    // expected output: "monster1 constructor called"

    const obj = new target(...args);

    // Return a Proxy instead of object. 
    // We may use the same handler1 here,or we can
    // create another handler with `get`. Both work,.
    return new Proxy(obj,handler1);
  },get(...args) {
    console.log('get trap triggered!')
    return Reflect.get(...args);
  }
};

const proxy1 = new Proxy(monster1,handler1);

const instance = new proxy1('fierce')

console.log(instance.disposition);
// expected output: "get trap triggered!"
// expected output: "fierce"

console.log(instance.unknownProp);
// expected output: "get trap triggered!"

我还没有尝试过，但是我认为super是您的答案。 https://www.w3schools.com/jsref/jsref_class_super.asp

javascript javascript-proxy