ajax防止表单自动提交

重写表单的checkForm方法，并用if和else解决异步判断的问题。

function checkForm(){
 1 var flag = false;    
 2 
 3 $.ajaxSetup({async : false});
 4 
 5 $.post(,'captcha='+document.getElementById("captcha").value,function(msg){if(!parseInt(msg)){layer.alert('验证码错误！',{time:1000});return flag;}else{
 6 
 7 $.post(,'username='+document.getElementById("username").value+'&'+'password='+document.getElementById("password").value,function(msg){if(!parseInt(msg)){layer.alert('用户名或密码错误！',{time:1000});return flag;}else{
 8 
 9 flag = true;return flag;}});}});
10 
11 return flag;
}