gistfile1.txt

const obj = {
  name: 'yamada',
  age: 17
};

const handler = {
  set: function(target, prop, value) {
    console.log(value)
    target[prop] = value.toUpperCase()
  },
  get: (target, prop)=> {
    console.log(target[prop])
    return target[prop].toUpperCase()
  }
}

const proxy = new Proxy(obj, handler)

proxy.name = 'takahashi' // ここでsetが実行される
console.log(proxy.name) // ここでgetが実行される