const person = {
  name: 'yk',
  age: 18
}

const personProxy = new Proxy(person, {
  get(target, property) {
    return property in target ? target[property] : 'default'
  },
  set(target, property, value) {
    if (property === 'age') {
      if (!Number.isInterage(value))
        throw new TypeError(`${value} is not an int`)

    }
    target[property] = value
  }
})