/**
 * @name placeholder
 * @class 跨浏览器placeholder,对于不支持原生placeholder的浏览器，通过value或插入span元素两种方案模拟
 * @param {object} obj 要应用placeholder的表单元素对象
 * @param {boolean} span 是否采用悬浮的span元素方式来模拟placeholder，默认值false,默认使用value方式模拟
 */
function placeholder(obj, span) {
	if("string" == typeof(obj)){obj=document.getelementbyid(obj);if(obj == null){return;}}
    if (!obj.getattribute('placeholder')) return;
    var imitatemode = span===true?true:false;
    var supportplaceholder = 'placeholder' in document.createelement('input');
    if (!supportplaceholder) {
        var defaultvalue = obj.getattribute('placeholder');
        if (!imitatemode) {
            obj.onfocus = function () {
                (obj.value == defaultvalue) && (obj.value = '');
                obj.style.color = '';
            };
            obj.onblur = function () {
                if (obj.value == defaultvalue) {
                    obj.style.color = '';
                } else if (obj.value == '') {
                    obj.value = defaultvalue;
                    obj.style.color = '#aca899';
                }
            };
            obj.onblur();
        } else {
            var placeholdercont = document.createtextnode(defaultvalue);
            var owrapper = document.createelement('span');
            owrapper.style.csstext = 'position:absolute; color:#aca899; display:inline-block; overflow:hidden;';
            owrapper.classname = 'wrap-placeholder';
            owrapper.style.fontfamily = getstyle(obj, 'fontfamily');
            owrapper.style.fontsize = getstyle(obj, 'fontsize');
            owrapper.style.marginleft = parseint(getstyle(obj, 'marginleft')) ? parseint(getstyle(obj, 'marginleft')) + 3 + 'px' : 3 + 'px';
            owrapper.style.margintop = parseint(getstyle(obj, 'margintop')) ? getstyle(obj, 'margintop'): 1 + 'px';
            owrapper.style.paddingleft = getstyle(obj, 'paddingleft');
            owrapper.style.width = obj.offsetwidth - parseint(getstyle(obj, 'marginleft')) + 'px';
            owrapper.style.height = obj.offsetheight + 'px';
            owrapper.style.lineheight = obj.nodename.tolowercase()=='textarea'? '':obj.offsetheight + 'px';
            owrapper.appendchild(placeholdercont);
            obj.parentnode.insertbefore(owrapper, obj);
            owrapper.onclick = function () {
                obj.focus();
            };
			//绑定input或onpropertychange事件
            if (typeof(obj.oninput)=='object') {
                obj.addeventlistener("input", changehandler, false);
            } else {
                obj.onpropertychange = changehandler;
            }
            function changehandler() {
                owrapper.style.display = obj.value != '' ? 'none' : 'inline-block';
            }
            /**
             * @name getstyle
             * @class 获取样式
             * @param {object} obj 要获取样式的对象
             * @param {string} stylename 要获取的样式名
             */
            function getstyle(obj, stylename) {
                var ostyle = null;
                if (obj.currentstyle)
                    ostyle = obj.currentstyle[stylename];
                else if (window.getcomputedstyle)
                    ostyle = window.getcomputedstyle(obj, null)[stylename];
                return ostyle;
            }
        }
    }
}