const data = {
text:'',
_text: ''
}
var textDom = document.querySelector('#text')
var inputDom = document.querySelector('#input')
Object.defineProperty(data, 'text', {
get(){
return this._text
},
set(val){
this._text = val
textDom.innerText = this._text
inputDom.value = this._text
}
})
document.querySelector('#input').addEventListener('keyup', function(e){
data.text = e.target.value
textDom.innerText = data._text
})
<input type="text" id="input" />
<p id="text"></p>