<div id="panel"><div/>

document.getElementById("panel").innerHTML = "sdfsd";

function Element(value, domEL){
this.domEl = domEL;            
this.domEl.getValue = function() { return value; };
this.domEl.setValue = function(newValue){ 
    var isChange = false || value!=newValue; 
    value = newValue; 
    if(isChange && this.onValueChange) this.onValueChange();  
};
this.domEl.buttonObj = this;    
this.domEl.onValueChange=this.valueChangeHandler;
}

Element.prototype.valueChangeHandler=function(){
var buttonObj = this.buttonObj;
alert('value is changed to '+ buttonObj.domEl.getValue());
}

var b = new Element(1, document.getElementById("panel")); 

    var Element = function(obj){
        this.element = obj;
        return this;
    }
    Element.prototype.innerHTML = function(txt, callBack) {
        var _arg = [];
        var _len = arguments.length;
        for(var i = 0; i < _len; i++) {
            _arg[i] = arguments[i];
        }
        var _oldTxt = this.element.innerHTML;
        this.element.innerHTML = _arg.shift();
        _arg.shift();
        callBack.apply(window, [_oldTxt, txt].concat(_arg));
    }
    var $Element = function(id) {
        var _obj = (typeof(id) == 'string')? document.getElementById(id) : id;
        return new Element(_obj);
    }

    function alertIt(oldTxt, newTxt, str) {
        alert(str);
    }
    $Element('box').innerHTML('ddd', alertIt, '内容改变了！');

------解决方案--------------------

目前DOM的标准没有暴露出这样一个接口，个人感觉，楼上的重载innerHTML的方式，要比setInterval好，最好还是修改下设计或者算法，这个需求还是有点怪。