how to detect input value change by javascript observe

1function changeValue (event, target) {
2    document.querySelector("#" + target).value = new Date().getTime();
3}
4 
5function changeContentValue () {
6    document.querySelector("#content").value = new Date().getTime();
7}
8 
9Object.defineProperty(document.querySelector("#content"), "value", {
10    set:  function (t) {
11        alert('#changed content value');
12        var caller = arguments.callee
13            ? (arguments.callee.caller ? arguments.callee.caller : arguments.callee)
14            : ''
15 
16        console.log('this =>', this);
17        console.log('event => ', event || window.event);
18        console.log('caller => ', caller);
19        return this.textContent = t;
20    }
21});