new to express & js and trying to understand next

Question

This is new to me and Im trying to learn so my terminology and code may be not be the best :).

I have code like below. createCustomer adds row to a table. My intention is if missing data then dont call the db function.

    try {
      if (!username || 
        !password || 
        !email || 
        !firstname || 
        !lastname || 
        !phone_number||
        !role) {
        next({
          name: "MissingCustomerDataError",
          message: "Required Field - username, password, email, firstname, lastname, phone_number"
        });
        // throw new RouteError({
        //     name: "MissingCustomerDataError",
        //     message: "Required Field - username, password, email, firstname, lastname, phone_number"
        //   });
      }
   ...(some more code)
      const cust = await createCustomer({ 
        username, 
        password, 
        email, 
        firstname, 
        lastname, 
        phone_number, 
        role, 
        address });

I would expect next(...) to "next" out of this logic and onto my error handler which I have attached after this route, but it still calls the db function. If I use throw it does seem to get out of this logic and into the catch block. Shouldnt next also leave this try block and move on? I think Im missing something conceptually. Thanks

Answer 1

Your expectation is wrong. A call of next starts the next middleware/request handler. It doesn't stop the current function. You can stop and leave a function with a return statement, e.g.:

if (!username || 
    !password || 
    !email || 
    !firstname || 
    !lastname || 
    !phone_number||
    !role) {
    return next({
      name: "MissingCustomerDataError",
      message: "Required Field - username, password, email, firstname, lastname, phone_number"
    });

or handle the error using a throw statement.