var el = document.getElementById('demo')
Object.defineProperties(el,
{
  innerHTML:{
      set:function(value){
        console.log('You change the property into ' + value)
        return value
      },
      get:function(){
        console.log('You got property value')
        return this.innerHTML
      }
	}
})

el.innerHTML='6666'
console.log(el.innerHTML)