测试是否支持DOMAttrModified

如果不支持propertychange事件,就使用这个,或者更高端的MutationObserver.

var root = document.documentElement 
 
 supportDOMAttrModified = root.addEventListener ?
  (function() {
    var fn,  f = false, id = root.id;
    fn = function() {
      root.removeEventListener('DOMAttrModified', fn, false);
      supportDOMAttrModified = true;
      root.id = id;//还原它
    };
    root.addEventListener('DOMAttrModified', fn, false);
    root.id = 'mass';//更新属性
    f = root.id != 'mass';
    root.id = id;//无论如何也还原它
    return f;
  })() :
  false

if(mutationObserver){//FF14+ (MutationObserver,无需前缀), Chrome18+(需Webkit前缀), 目前只有这两款浏览器有实现.
                   /*
                       参考 :
                       1.  http://www.w3.org/TR/dom/#mutation-observers
                       2.  https://hacks.mozilla.org/2012/05/dom-mutationobserver-reacting-to-dom-changes-without-killing-browser-performance/
                   */
                   observer = new mutationObserver(
                       function(mutations){
                           
                           //mutations[mutations.length].oldValue //老的值
                           onchange();
                       }
                   );
                   observer.observe(
                       el,
                       {
                           //attributeOldValue : true, //mutation record 记录前一个值.
                           attributes : true,
                           attributeFilter : 'value' //只关注value 的变化.
                       }
                   );
                   //observer.disconnect();
                   
               }else if(el.addEventListener && !window.XDomainRequest){//FF2+, Opera9.2+, IE9+
                   el.addEventListener('DOMAttrModified', function (e) {
                       /*
                           注意,这货只对js修改敏感.
                           所以,需要结合你关注属性的其他DOM事件
                           比如input 的 oninput,onchange 什么的.
                       */
                       alert(e.attrName)
                       if(e.attrName === 'value'){
                           onchange();
                       }
                   }, false);
               }else if(el.attachEvent){
                   el.attachEvent('onpropertychange', function (e) {
                       if(e.propertyName === 'value'){
                           onchange();
                       }
                      
                   });
               }
 
document.onclick = function () {
               el.value = Math.random();
               //el.setAttribute('value', Math.random());
               el.name = 123; //opera10+,FF2+,IE9+ (有趣的是, DOMAttrModified的 e.attrName ,IE9下,对于name 居然叫做 propdescname ..)
               el.setAttribute('name', 1234); //opera9.2+, FF2+,IE9+
               
               /*
                   建议为了只使用el.value 方式修改value的值. 这样做,虽然会损失opera9.6-. 但却可以解决一个致命问题.
                   即,非IE9一旦某处,使用过el.value = xxx的方式后 el.setAttribute('value', xxx); 就失效了...即不改变value，也不会触发 DOMAttrModified 以及 observer的回调.
                   IE9 则很变态,el.value= xxx方式只能触发 onpropertychange, setAttribute方式,则只能触发DOMAttrModified.
                   (IE6-8没这个问题,因为IE6-8不区分attribute和property.所以无论咋折腾它都触发onpropertychange)
                   所以综合考虑下,IE9+也同样使用onpropertychange, 且保证修改value,一概使用el.value = xxx方式.
                   
               */