原地址：http://www.cnblogs.com/larennani/p/6839139.html

<script type="text/javascript">
    $(function(){
        if(!placeholderSupport()){   // 判斷瀏覽器是否支援 placeholder
            $('[placeholder]').focus(function() {
                var input = $(this);
                if (input.val() == input.attr('placeholder')) {
 

                    input.val('');
                    input.removeClass('placeholder');
                }
            }).blur(function() {
                var input = $(this);
                if (input.val() == '' || input.val() == input.attr('placeholder')) {
                    input.addClass('placeholder');
 

                    input.val(input.attr('placeholder'));
                }
            }).blur();
        };
    })
    function placeholderSupport() {
        return 'placeholder' in document.createElement('input');
    }
</script>