如何在可构造的JavaScript对象上为属性创建陷阱

Question

Proxy有一个new运算符的陷阱，理论上它应该允许我们创建将构造函数参数传递到目标对象的Proxy。它的工作原理示例如下：

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

这非常有效。除了CCD_ 2现在不再触发CCD_ 3陷阱。现在如何拦截属性？

Answer 1

在Construct内部有return new target(...args);。这创建了一个新的JS对象，没有设置任何代理。

您应该在新创建的对象上设置一个额外的代理，以拦截对该对象的属性访问。

像这样：

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!"

Answer 2

我还没有试过，但我认为super是你的答案。https://www.w3schools.com/jsref/jsref_class_super.asp