JS Proxy对象使用的两个案例：校验器和属性私有化

校验器

const target = {
  _id: '1024',
  name: 'vuejs',
}
 
// 校验器
const validators = {
   name(val) {
     return Object.prototype.toString.call(val) === 'string';
   },
   _id(val) {
     return Object.prototype.toString.call(val) === 'number';
   }
}
 
const createValidator = (target, validators) => {
  return new Proxy(target, {
    _validator: validators,
    set(target, propKey, value, proxy) {
      let validator = this._validator[propKey](value)
      if(validator) {
        return Reflect.set(target, propKey, value, proxy)
      } else {
        throw Error(`无法设置属性为${propKey}的值为${value}，类型不匹配`)
      }
    }
  })
}
 
const targetProxy = createValidator(target, validators)
 
// targetProxy.name = 1234 // Error: 无法设置属性为name的值为1234，类型不匹配
// targetProxy._id = '1234' // Error: 无法设置属性为_id的值为1234，类型不匹配

属性私有化

const target = {
  _id: '1024',
  name: 'vuejs',
}
 
 
 
const createProxy = (target) => {
  return new Proxy(target, {
    get: function(target, propKey, proxy) {
      if(propKey[0] === '_') {
        throw Error(`${propKey} is privated`)
      }
      return Reflect.get(target, propKey, proxy)
    },
    set: function(target, propKey, value, proxy) {
      if(propKey[0] === '_') {
        throw Error(`${propKey} is privated, can not set ${value}`)
      }
      return Reflect.set(target, propKey, value, proxy)
    }
  })
}
 
const targetProxy = createProxy(target)
 
// targetProxy._id = 123 // Error: _id is privated, can not set 123
// console.log(targetProxy._id) // Error: _id is privated