$(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‘);}原文：http://www.cnblogs.com/frxing/p/5070550.html