var doc = window.document, input = doc.createElement('input');
if( typeof input['placeholder'] == 'undefined' ) // 如果不支持placeholder属性
{
$('input').each(function( ele )
{
var me = $(this);
var ph = me.attr('placeholder');
if( ph && !me.val() )
{
me.val(ph).css('color', '#aaa').css('line-height', me.css('height'));
}
me.on('focus', function()
{
if( me.val() === ph)
{
me.val(null).css('color', '');
}
}).on('blur', function()
{
if( !me.val() )
{
me.val(ph).css('color', '#aaa').css('line-height', me.css('height'));
}
});
});
}