input和propertychange方法

绑定
```
 * @param {Object} obj
 * @param {String} eventType
 * @param {Function} fn
 */
function addEvent(obj, eventType, fn) {
    if (obj.addEventListener) {
        obj.addEventListener(eventType, fn, false);
    } else if (obj.attachEvent) {
        obj.attachEvent('on' + eventType, fn);
    } else {
        obj['on' + eventType] = fn;
    }
}

/**
 * 请根据提示，完成兼容IE低版本input的oninput和propertychange方法绑定
 * @param {Object} obj
 * @param {String} eventType
 * @param {Function} fn
 */
function addEvent(obj, eventType, fn) {
    if (obj.addEventListener) {
        obj.addEventListener(eventType, fn, false);
    } else if (obj.attachEvent) {
        // 兼容IE8及以下
        obj.attachEvent('on' + eventType, function() {
            if (eventType === 'input') {
                fn();
            }
        });
        obj.attachEvent('onpropertychange', function() {
            if (event.propertyName === 'value') {
                fn();
            }
        });
    } else {
        obj['on' + eventType] = fn;
    }
}
```