Proxy与Reflect

Proxy概述

var obj = new Proxy({}, {
	get: function(target, key, receiver){
		console.log(`getting ${key}!`);
		return Reflect.get(target, key , receiver);
	},
	set: function(target, key, value, receiver) {
		console.log(`setting ${key} : ${value}`);
		return Reflect.set(target, key, value + 1, receiver);
	}
});

obj.count = 1;

console.info(obj.count);

// setting count : 1
// getting count!
// 2

• Proxy原意代理
• 可以用来修改某些操作的默认行为，等同于在语言层面作出修改，属于一种元编程

语法

var proxyobj = new Proxy( target, handler );

 通过Proxy构造函数来生成代理对象
 target是代码的原始对象
 handler是代理处理代码, 用来定制拦截行为；也是对象

支持的拦截操作一览

• get(target, propKey, receiver)
• set(target, propKey, propValue, receiver)
• has(target, propKey)
• deleteProperty(target, propKey)
• enumerate(target)
• ownKeys(target)
• getOwnPropertyDescriptor(target, propKey)
• defineProperty(target, propKey, propDesc)
• preventExtensions(target)
• getPrototypeOf(target)
• isExtensible(target)
• setPrototypeOf(target, proto)
• apply(target, object, args)
• construct(target, args, proxy)

Proxy.revocable()

• Proxy.revocable方法可返回一个可取消的Proxy实例

let target = {};
let  handler = {};

let {proxy, revoke} = Proxy.revocable( target, handler );
proxy.foo = 123;
proxy.foo // 123

revoke(); //取消proxy实例
proxy.foo // TypeError：Revoked

Reflect概述

• 将某些明显属于语言内部的方法，放到Reflect对象上；比如：Object.defineProperty
• 修改某些Object方法的返回结果，让其变得更合理。比如

try{
	Object.defineProperty(target, property, atributes);
}catch(err){}

if(Reflect.defineProperty(target,property, attributes) ) {
	
}

• 放Object操作行为变为函数行为 delete in
• Reflect对象的方法与Proxy对象的方法一一对应

Reflect对象的方法

• Reflect.apply(target,thisArg,args)
• Reflect.construct(target,args)
• Reflect.get(target,name,receiver)
• Reflect.set(target,name,value,receiver)
• Reflect.defineProperty(target,name,desc)
• Reflect.deleteProperty(target,name)
• Reflect.has(target,name)
• Reflect.ownKeys(target)
• Reflect.enumerate(target)
• Reflect.isExtensible(target)
• Reflect.preventExtensions(target)
• Reflect.getOwnPropertyDescriptor(target, name)
• Reflect.getPrototypeOf(target)
• Reflect.setPrototypeOf(target, prototype)