Node JS + Express应用程序中的错误处理

Question

I am writing a small web-app using Node JS (version 8.4.0), Express (version 4.15.3) and using Passport (version 0.3.2) for authentication.

I am using PostgreSQL 9.6 for database.

I am not able to understand how to handle errors using Promises in my application.

I have divided my app into routes (has information related to which routes to handle via http requests), views (handlebars templates to render pages) and model (functions related to database queries).

Here is an example code from a model:

var helpers = require('./helpers'); //Has a function to perform db queries

exports.getCustomerDetails = (cust_id,cb)=>{

    var qs = 'select * FROM customers WHERE cust_id=($1)';
    var params = [cust_id];

    helpers.dbquery(qs,params,(error,results)=>{

        if(error){
            return cb(error);
        }

        return cb(null,results);

    });

}

At present, what I am doing in the corresponding route handler is to send HTTP 500 as response.

//Get Customer details based on cust_code as input

router.get('/getCustomerDetails',(req,res,next)=> {
    if (req.user) {

      var cust_code = req.query.value;

      db.getCustomerDetails(cust_code, (error, result) => {

        if (error) {
          res.sendStatus(500);
        }
        res.status(200).send(result);
      });
    } else {
      res.sendStatus(401);
    }
})

I want to understand what is the best way to handle errors at both levels, ie route and database.

I read a few articles on error handling and searched Stackoverflow, but I am not able to wrap my head around it being a beginner in any sort of development.

Please suggest how to handle errors in my web-app and any references which could help me understand error handling in web-apps.

Answer 1

The following could do what you ask for. Create a promise, catch the reject of that promise and return the promise you created but not with the catch so the caller can catch the reject again.

var helpers = require('./helpers'); //Has a function to perform db queries

exports.getCustomerDetails = (cust_id, cb) => {
  var qs = 'select * FROM customers WHERE cust_id=($1)';
  var params = [cust_id];
  //create a promise
  const p = new Promise(
    (resolve,reject) =>
      helpers.dbquery(qs, params, (error, results) =>
        (error)
          ? reject(error)
          : resolve(results)
      )
  );
  //catch the reject
  p.catch(
    error => {
      //... do something with the error on the db level
    }
  );
  //return the promise that DID NOT have the error caught
  return p;
};


router.get('/getCustomerDetails',(req,res,next)=> {
  if (req.user) {
    var cust_code = req.query.value;
    //getCustomerDetails returns a promise
    db.getCustomerDetails(cust_code)
    .then(
      result =>
        res.status(200).send(result)
    )
    .catch(
      error =>
      res.sendStatus(500)
    )
  } else {
    res.sendStatus(401);
  }
});

Answer 2

From my point of view the best way is to handle all errors in routes layer, in order to format them properly according to the interface. Imagine in the future you change your REST API layer by a GraphQL layer, with this approach you just have to modify this layer, and not the rest. The way to throw all errors from other layers: I usually create an Error object and add several custom properties, for example:

var error = Error();
error.code = 401;
error.log = true;
error. translate = true;
error.message = "Unauthorized";
....
throw error;

And in the routes layer, you can catch the error and create the custom response with all the data. It is flexible and powerful.

Hope it helps.