Handling 503 Error in Express/Node.js especially in TryCatch case

Question

I have a special case for which I want to clear the possible reason for 503 Error. The following code snippet has a catch statement which runs when system is not able to find any results

app.post('/api/fetch/user', function(req, res){
   var email = req.body.emailTxt;
   db.one('SELECT * FROM users WHERE email=$1', [email])
       .then(function(data){
           console.log('DATA:', data);

           var userCard = { id: data.user_id, name: data.user_name, 
                            email: data.email, regDate: data.date_created };

           res.status(200).json({ 'valid': true, '_payload': userCard });
       })
       .catch(function(error){
           if(error.search(/No data returned from the query/im) > 0)    // regex case insensitive search and search multiline as source string is multiline
              res.status(500).send('Invalid Request Match');
           else 
              res.status(500).send('ERROR: '+error);
       })

});

When my API call is made to this API end point and when no result found the control moves in catch() which is fine but quite strangely it returns 503 - Request timeout error. I have tried to to remove conditions in if() in order to debug but seems like no matter what but the if-else does not seem working in ExpressJs.

Note: Everything works well and also when control stays in .then(). If I remove if,else and keep simple error display/response return then everything works ok. There is nothing special included in my API; it is only one single page script I prepared to test API.

iKoala · Accepted Answer · 2016-11-25T11:54:26.490

I think you got error in the .catch block.

Try to modify the code and see if this helps:

app.post('/api/fetch/user', function(req, res){
     var email = req.body.emailTxt;
     db.one('SELECT * FROM users WHERE email=$1', [email])
         .then(function(data){
             console.log('DATA:', data);

             var userCard = { id: data.user_id, name: data.user_name, 
                              email: data.email, regDate: data.date_created };

             res.status(200).json({ 'valid': true, '_payload': userCard });
         })
         .catch(function(error){
           console.error(error); //never ignore errors!
           try {
             //i think error is an Error Object here, so it doesn't have .search function
             if(error.search(/No data returned from the query/im) > 0)    // regex case insensitive search and search multiline as source string is multiline
                res.status(500).send('Invalid Request Match');
             else 
                res.status(500).send('ERROR: '+error);
           } catch (err) {
             console.error(err);
              res.status(500).send('some unknown error');
           };
         });
      });

Edit: Sorry, removed .finally because you may send response twice.
Edit, better approach to handle error in .catch block.

//make catch block error safe to make sure no error occurs
if (error && error.message == 'No data returned from the query.') {
  res.status(500).send('Invalid Request Match');
} else {
  res.status(500).send('ERROR: '+error);
}

One typo though, the `catch` you mentioned does not take function and only allows to pass a parameter. Yes, you have pointed to the right direction that the `error` does not have `.search()`. What should I do in this case if I want to parse the error message string? The error appears in following way on console (in multiline): `ERROR: QueryResultError { code: queryResultErrorCode.noData message: "No data returned from the query." received: 0 query: "SELECT * FROM users WHERE email='hannan@designsoftstudios.com' AND password='1234'" }` — Nah, Nov 25 '16 at 11:29
Hurrey!! solved the issue as per your directions. Have parse the `error` object to string using `error.toString();` as the `.toString()` is a global method and it worked for me. — Nah, Nov 25 '16 at 11:43
Since your database return proper `QueryResultError`, I think you can make it error safe in the `catch` block. Edited the answer with better approach to handle errors. — iKoala, Nov 25 '16 at 11:55

Nah · Answer 2 · 2016-11-25T11:41:34.950

We use response codes in ExpressJs quite intensively when creating an API service. So it seems a right way that we make use of them directly instead of doing if-else in catch().

Hence, the right way would be:

.catch(function(error){
        console.log('ERROR:', error);
        res.status(204).send('No Content; Invalid Request Match');
    })

However, If you want to display/return detailed message you can do that as well. You can check: http://expressjs.com/en/api.html#res for details on ways you can response back. You can render an HTML template, or return JSON response or even multiline text.

I don't know why if-else creates problem but you can go other way around.

In your specific case the error does not have .search() method attached to it. So better to parse it to string first using .toString();.

Handling 503 Error in Express/Node.js especially in TryCatch case

2 Answers2