js实现页面的秒数倒计时

<button name="vcode_mail" class="btn btn-default" type="button" id="vcode_mail-btn" onclick="vcode_mail_post(this)">免费获取验证码</button>

 ???//发送验证码 ???function vcode_mail_post(obj){ ???????var seconds =121; ???????//获取邮箱 ???????var email = $("input[name=‘email‘]").val(); ???????//异步变同步 ???????/*$.ajaxSettings.async = false;*/ ???????//发送请求 ???????$.post("{:url(‘index/user/vcode_mail_post‘)}",{email:email,type:1},function(data){ ???????????var message = data.message; ???????????if(data.ok == ‘1‘){ ???????????????alert(message); ???????????????//倒计时 ???????????????daojishi(seconds,obj); ???????????????}else{ ???????????????alert(message); ???????????} ???????},‘json‘); ???????/*$.ajaxSettings.async = true;*/ ???} ???//倒计时 ???function daojishi(seconds,obj){ ???????if (seconds > 1){ ???????????????seconds--; ???????????????$(obj).text(seconds+"秒后可重新获取 ").attr("disabled", true);//禁用按钮 ???????????????// 定时1秒调用一次 ???????????????setTimeout(function(){ ???????????????????daojishi(seconds,obj); ???????????????},1000); ???????????}else{ ???????????????$(obj).text("重新获取验证码").attr("disabled", false);//启用按钮 ???????????} ???????????}