創(chuàng)建一個簡單的Proxy

let target = {} let proxy = new Proxy(target, {})  proxy.name = 'proxy'  console.log(proxy.name) // proxy console.log(target.name) // proxy  target.name = 'target'  console.log(proxy.name) // target console.log(target.name) // target

這個實例將"proxy"賦值給proxy.name屬性時會在目標(biāo)上創(chuàng)建name,代理只是簡單的將操作轉(zhuǎn)發(fā)給目標(biāo)，他不會儲存這個屬性。相當(dāng)于proxy.name和target.name引用的都是target.name的值。

使用set陷阱驗證屬性

set陷阱接收四個參數(shù)：

1.trapTarget：用于接收屬性（代理的目標(biāo)）的對象

2.key：要寫入的屬性鍵（字符串或者symbol）

3.value：被寫入的屬性值

4.receiver：操作發(fā)生的對象（通常是代理）

let target = {     name: "target" }  let proxy = new Proxy(target, {     set(trapTarget, key, value, receiver) {         if (!trapTarget.hasOwnProperty(key)) {             if (isNaN(value)) {                 throw new TypeError("屬性必須時數(shù)字")             }         }          return Reflect.set(trapTarget, key, value, receiver)     } })  proxy.count = 1 console.log(proxy.count) //1 console.log(target.count) //1  proxy.name = "proxy"  console.log(proxy.name) //proxy console.log(target.name) //proxy  proxy.other = "other" // 這里會報錯因為不數(shù)字

這個實例每次在外面改變proxy的值時就會出發(fā)set函數(shù)。

用get陷阱驗證對象結(jié)構(gòu)

get接收3個參數(shù)

1.trapTarget：用于接收屬性（代理的目標(biāo)）的對象

2.key：要寫入的屬性鍵（字符串或者symbol）

3.receiver：操作發(fā)生的對象（通常是代理）

let proxy = new Proxy({}, {     get(trapTarget, key, receiver) {         if (!(key in receiver)) {             throw new TypeError("屬性" + key + "不存在")         }          return Reflect.get(trapTarget, key, receiver)     } })  proxy.name = "proxy"  console.log(proxy.name) //proxy  console.log(proxy.age) // 屬性不存在會拋出錯誤

當(dāng)我們訪問proxy創(chuàng)建的對象屬性時就會觸發(fā)get方法

使用has陷阱因此已有屬性

has接收2個參數(shù)：

1.trapTarget：用于接收屬性（代理的目標(biāo)）的對象

2.key：要寫入的屬性鍵（字符串或者symbol）

let target = {     name: "target",     value: 42 }  let proxy = new Proxy(target, {     has(trapTarget, key) {         if (key === 'value') {             return false         } else {             return Reflect.has(trapTarget, key)         }     } })   console.log("value" in proxy) // false console.log("name" in proxy) // true console.log("toString" in proxy) // true

用deleteProperty陷阱防止刪除屬性

deleteProperty接收2個參數(shù)：

1.trapTarget：用于接收屬性（代理的目標(biāo)）的對象

2.key：要寫入的屬性鍵（字符串或者symbol）

let target = {     name: "target",     value: 42 }  let proxy = new Proxy(traget, {     deleteProperty(trapTarget, key) {         if (key === "value") {             return false         } else {             return Reflect.deleteProperty(trapTarget, key)         }     } })   console.log("value" in proxy) // true  let result1 = delete proxy.value  console.log(result1) // false console.log("value" in proxy) // true  console.log("name" in proxy) // true  let result2 = delete proxy.name console.log(result2) // true console.log("name" in proxy) // false

當(dāng)外部要刪除proxy的屬性就會觸發(fā)deleteProperty函數(shù)

原型代理陷阱(setProptotypeOf,getPrototypeOf)

setProptotypeOf接收2個參數(shù)

1.trapTarget：用于接收屬性（代理的目標(biāo)）的對象

2.proto：作為原型使用的對象

let target = {}  let proxy = new Proxy(target, {      // 訪問時調(diào)用     getPrototypeOf(trapTarget) {         return null     },     // 改變時調(diào)用     setPrototypeOf(trapTarget, proto) {         return false     }  })  let targetProto = Object.getPrototypeOf(target) let proxyProto = Object.getPrototypeOf(proxy)  console.log(targetProto === Object.prototype) //true console.log(proxyProto === Object.prototype) // false console.log(proxyProto) // null  Object.setPrototypeOf(target, {}) // 成功  Object.setPrototypeOf(proxy, {}) // 拋出錯誤

如果正常實現(xiàn)

let target = {}  let proxy = new Proxy(target, {      // 訪問時調(diào)用     getPrototypeOf(trapTarget) {         return Reflect.getPrototypeOf(trapTarget)     },     // 改變時調(diào)用     setPrototypeOf(trapTarget, proto) {         return Reflect.setPrototypeOf(trapTarget, proto)     }  })  let targetProto = Object.getPrototypeOf(target) let proxyProto = Object.getPrototypeOf(proxy)  console.log(targetProto === Object.prototype) //true console.log(proxyProto === Object.prototype) // true  Object.setPrototypeOf(target, {}) // 成功  Object.setPrototypeOf(proxy, {}) // 成功

屬性描述符陷阱

defineProperty接收三個參數(shù)：

1.trapTarget：用于接收屬性（代理的目標(biāo)）的對象

2.key：要寫入的屬性鍵（字符串或者symbol）

3.descriptor：屬性的描述對象

let proxy = new Proxy({}, {     defineProperty(trapTarget, key, descriptor) { // descriptor 只能接收enumerable, configurable, value, writeable, get, set          if (typeof key === "symbol") {             return false         }         return Reflect.defineProperty(trapTarget, key, descriptor)     },     getOwnPropertyDescriptor(trapTarget, key) {         return Reflect.getOwnPropertyDescriptor(trapTarget, key)     } })  Object.defineProperty(proxy, "name", {     value: "proxy" })  console.log(proxy.name) //proxy  let nameSymbol = Symbol("name")  Object.defineProperty(proxy, nameSymbol, {     value: "proxy" })

在外部調(diào)用defineProperty | getOwnPropertyDescriptor時會觸發(fā)內(nèi)部definenProperty | getOwnPropertyDescriptor方法。

ownKeys陷阱

ownKeys陷阱會攔截外部的Object.keys()，Object.getOwnPropertyName(),Object.getOwnPropertySymbols()和Object.assign()四個方法

let proxy = new Proxy({}, {     ownKeys(trapTarget) {         return Reflect.ownKeys(trapTarget).filter(key => {             return typeof key !== "string" || key[0] !== '_'         })     } })  let nameSymbol = Symbol("name")  proxy.name = "proxy"  proxy._name = "private"  proxy[nameSymbol] = "symbol"  let names = Object.getOwnPropertyNames(proxy),     keys = Object.keys(proxy),     symbols = Object.getOwnPropertySymbols(proxy)  console.log(names.length) // 1 console.log(names) // name  console.log(keys.length) //1 console.log(keys[0]) // name  console.log(symbols.length) //1 console.log(symbols[0]) // symbol(name)