理解JavaScript中的Proxy 与 Reflection API

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

let target = {
 name: "target"
}

let proxy = new Proxy(target, {
 set(trapTarget, key, value, receiver) {
  if (!trapTarget.hasOwnProperty(key)) {
   if (isNaN(value)) {
    throw new TypeError("New property must be a number.")
   }
  }
  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.anotherName = "proxy"
// TypeError: New property must be a number.

let target = {}
console.log(target.name) // undefined

let proxy = new Proxy({}, {
 get(trapTarget, key, receiver) {
  if (!(key in receiver)) {
   throw new TypeError("Property " + key + " doesn't exist.")
  }
  return Reflect.get(trapTarget, key, receiver)
 }
})

proxy.name = "proxy"
console.log(proxy.name) // proxy

console.log(proxy.nme)
// TypeError: Property nme doesn't exist.

let target = {
 name: "target",
 value: 42
}

Object.defineProperty(target, "name", { configurable: false })
console.log("value" in target)  // true

let result1 = delete target.value
console.log(result1)       // true
console.log("value" in target)  // false

let result2 = delete target.name
console.log(result2)       // false
console.log("name" in target)   // true

let target = {
 name: "target",
 value: 42
}

let proxy = new Proxy(target, {
 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

let result2 = delete proxy.name
console.log(result2)       // true
console.log("name" in proxy)   // false

function makeLoggable(target) {
 return new Proxy(target, {
  get: (target, property) => {
   console.log("Reading " + property)
   return target[property]
  },

  set: (target, property, value) => {
   console.log("Writing value " + value + " to " + property)
   target[property] = value
  }
 })
}

let ninja = { name: "Yoshi" }
ninja = makeLoggable(ninja)

console.log(ninja.name)
ninja.weapon = "sword"
// Reading name
// Yoshi
// Writing value sword to weapon

function isPrime(number) {
 if (number < 2) { return false }

 for (let i = 2; i < number; i++) {
  if (number % i === 0) { return false }
 }
 return true
}

isPrime = new Proxy(isPrime, {
 apply: (target, thisArg, args) => {
  console.time("isPrime")
  const result = target.apply(thisArg, args)
  console.timeEnd("isPrime")
  return result
 }
})

console.log(isPrime(1358765377))
// isPrime: 6815.107ms
// true

function Folder() {
 return new Proxy({}, {
  get: (target, property) => {
   console.log("Reading " + property)

   if(!(property in target)) {
    target[property] = new Folder()
   }
   return target[property]
  }
 })
}

const rootFolder = new Folder()
rootFolder.ninjasDir.firstNinjaDir.ninjaFile = "yoshi.txt"
// Reading ninjasDir
// Reading firstNinjaDir
console.log(rootFolder.ninjasDir.firstNinjaDir.ninjaFile)
// Reading ninjasDir
// Reading firstNinjaDir
// Reading ninjaFile
// yoshi.txt