$(function(){if(!placeholderSupport()){   // 判断浏览器是否支持 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‘);}