如何在发送回应后停止nodejs ajax请求代码

Question

我正在Nodejs中实现一个简单的用户注册表单。我正在使用Express框架，Mongodb和Monk。我成功地实现了正常的数据库插入。但现在，当我添加代码来首先检查输入的电子邮件或用户名是否存在时，它已经不存在了。问题是，当发现有相同电子邮件或用户名的条目时，我使用res.end发送错误响应，但代码不会停在那里并继续执行其他条件，并最终插入文档而不考虑条件，有时会给出错误can't set headers after they are sent。下面是我对ajaxsignup航线代码

router.post('/ajaxsignup', function(req, res){ 
var db = req.db; 
var formdata = req.body; 

var collection = db.get('userscollection'); 

res.setHeader('Content-Type', 'application/json'); 

var emailExists = collection.findOne({"email": formdata.email}, function(err, doc){ 
    if(err) 
    { 
     response = {'status': 0, 'err_code': err.code, 'err_msg': err.err}; 
     res.end(JSON.stringify(response)); 
    } 
    else 
    { 
     if(doc) 
     { 
      response = {'status': 0, 'err_code': 0, 'err_msg': 'This email id is already registered. Please use a different one.'};    
      res.end(JSON.stringify(response)); 
     } 
    } 
});//emailExists 

var usernameExists = collection.findOne({"username": formdata.username}, function(err, doc){ 
    if(err) 
    { 
     response = {'status': 0, 'err_code': err.code, 'err_msg': err.err}; 
     res.end(JSON.stringify(response)); 
    } 
    else 
    { 
     if(doc) 
     { 
      response = {'status': 0, 'err_code': 0, 'err_msg': 'This username is already in use. Please use a different one.'};    
      res.end(JSON.stringify(response)); 
     } 
    } 
});//usernameExists 



formdata.created = new Date(); 
formdata.last_updated = formdata.created; 

collection.insert(formdata, function(err, doc){ 
    if(err) 
    { 
     response = {'status': 0, 'err_code': err.code, 'err_msg': err.err}; 
    } 
    else 
    { 
     response = {'status': 1, 'msg': 'Thank you. You can proceed to login now.'}; 
    } 

    res.end(JSON.stringify(response)); 
});//insert 
});//ajaxsignup 

Answer 1

不能设置头，他们被送到这个错误之后，因为你写res.end三个时间 有几种方法可以做到这一点

1）使蒙戈电子邮件和用户名和独特当您尝试插入一个已经存在则返回错误的电子邮件或用户名

new Schema{ 
    email:{type:String,index: { unique: true },required:true} 
    username:{type:String,index: { unique: true },required:true} 
} 






collection.insert(formdata,function(err,data){ 
     if(err){ 
     res.json({success:false,text:"User with this email or username already exists!"}); 
     } 
     else{ 
     res.json({success:true,text:"Your registration was successfull"}); 
     } 
    }) 

2）第二个是你的方式

var emailExists=false,usernameExists=false; 
collection.findOne({"$or":[{"email": formdata.email},{"username":formdata.username}], function(err, doc){ 
    if(err) 
    { 
     response = {'status': 0, 'err_code': err.code, 'err_msg': err.err}; 
     res.end(JSON.stringify(response)); 
    } 
    else 
    { 
     if(!doc) 
     { 
     collection.insert(formdata, function(err, doc){ 
    if(err) 
    { 
     response = {'status': 0, 'err_code': err.code, 'err_msg': err.err}; 
    } 
    else 
    { 
     response = {'status': 1, 'msg': 'Thank you. You can proceed to login now.'}; 
    } 

    res.end(JSON.stringify(response)); 
});//insert 
}); 
     }else{ 
      response = {'status': 0, 'err_code': 0, 'err_msg': 'This email id is already registered. Please use a different one.'};    
      res.end(JSON.stringify(response)); 
     } 
    } 
});