Understanding Proxy in es6 (with examples)

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Test question analysis: The understanding of proxy may extend to the two-way binding of vue

Proxy (proxy) definition

can be understood as The target object has a layer of interception, and external access to the object must pass through this layer of interception

Simple example:

 const obj = new Proxy({}, {
     get: (target, key, receiver) => {
         return 'JS'
         console.log(`get ${key}`)
     },
     set: (target, key, value, receiver) => {
         console.log(`set ${key}`)
     },
 })
 
 obj.name = 'JS 每日一题' 
 // set name
 // JS 每日一题
 
 obj.name 
 // 这里进入get的回调函数，所有直接返回 JS

As can be seen from the above example, there is a mechanism for Proxy , you can rewrite external read and write operations

Proxy instance method

In addition to proxying get and set operations, proxy can also proxy other operations, as follows

handler.getPrototypeOf()

// 在读取代理对象的原型时触发该操作，比如在执行 Object.getPrototypeOf(proxy) 时。

handler.setPrototypeOf()

// 在设置代理对象的原型时触发该操作，比如在执行 Object.setPrototypeOf(proxy, null) 时。

handler.isExtensible()

// 在判断一个代理对象是否是可扩展时触发该操作，比如在执行 Object.isExtensible(proxy) 时。

handler.preventExtensions()

// 在让一个代理对象不可扩展时触发该操作，比如在执行 Object.preventExtensions(proxy) 时。

handler.getOwnPropertyDescriptor()

// 在获取代理对象某个属性的属性描述时触发该操作，比如在执行 Object.getOwnPropertyDescriptor(proxy, "foo") 时。

handler.defineProperty()

// 在定义代理对象某个属性时的属性描述时触发该操作，比如在执行 Object.defineProperty(proxy, "foo", {}) 时。

handler.has()

// 在判断代理对象是否拥有某个属性时触发该操作，比如在执行 "foo" in proxy 时。

handler.get()

// 在读取代理对象的某个属性时触发该操作，比如在执行 proxy.foo 时。

handler.set()

// 在给代理对象的某个属性赋值时触发该操作，比如在执行 proxy.foo = 1 时。

handler.deleteProperty()

// 在删除代理对象的某个属性时触发该操作，比如在执行 delete proxy.foo 时。

handler.ownKeys()

// 在获取代理对象的所有属性键时触发该操作，比如在执行 Object.getOwnPropertyNames(proxy) 时。

handler.apply()

// 在调用一个目标对象为函数的代理对象时触发该操作，比如在执行 proxy() 时。

handler.construct()

// 在给一个目标对象为构造函数的代理对象构造实例时触发该操作，比如在执行new proxy() 时。

Why do you want to Use Proxy

• Intercept and monitor external access to objects

• Reduce the complexity of functions or classes

• Verify operations or manage required resources before complex operations

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