猫鼬：为什么我没有收到错误响应

Question

每次我输入错误的用户时我都写了这条路线来查找用户我没有得到 res.json() msg​​

app.post('/authenticate', function(req, res){

    user.findOne({email : req.body.username}, function(err, user){
          if(err){
            res.json('user not found');  //not getting this 
          }else{  
            console.log(user);  //probably this ran, cuz getting null at cmd
          }
    })
})

Answer 1

当用户名与任何文档不匹配时，它返回空用户json。错误 err object is null so res.json is unreachable ，所以你必须通过

app.post('/authenticate', function(req, res){

        user.findOne({email : req.body.username}, function(err, user){
              if(err){
                throw err;
              }else{ 
                if(user){
                  console.log(user);  //probably this ran, cuz getting null at cmd
                }else{
                  console.log("User Not Found");
                }

              }
        })
    })