How do I throw errors from an action in Seneca?

Question

I'm working on a simple task manager in SenecaJS, and I'm trying to understand the correct way to throw errors from an action. Say I've got an action which loads a task from a datastore, and the task doesn't exist...

Below is the method from my plugin:

/**
 * Retrieves a task based on a task ID.
 *
 * @param  {number} args.taskID The UUID of the task to be retrieved.
 * @param  {function} done A callback function which is called upon retrieval. The
 * first argument is an error response; the second is the task.
 * @returns {Task|undefined} A task if one exists; otherwise undefined.
 */
this.get = function(args, reply) {
  var task = this.make('task')
    task.load$( args.taskID, function(err, task) 
      if(!task || err) {
      reply( {code:404, message:`Task ${args.taskID} not found.`} );
    } else {
      reply( task );
    }
  });
};

And this is the unit test:

test('Returns "undefined" for non-existant tasks', (fin) => {
  var seneca = testSeneca(fin);
  var id = "I-don't-exist";
  seneca
    .act(
      { domain: 'task', action: 'get', taskID: id },
      function(err, result) {
        expect(result).not.toBeNull();
        expect(result.code).toBe(404);
        fin();
      }
    );
});

The code below works, but as you can see I am really ignoring the err callback and evaluating the result to see if it's an error or not. In the documentation, Seneca uses the following to throw an error:

reply( new Error(404) );

or

throw new Error(404);

But when I do that, it ends the process and the unit test fails. Furthermore, the err callback always seems to be null, even if I reply with two objects.

Is there a more correct way to return errors that utilizes the err callback?

score 0 · Answer 1 · answered Jul 25 '19 at 23:50

You may be using a plugin definition instance to call normal actions - errors in this case are always fatal as they mean initialization has failed.

Try

this.get = function(args, reply, meta) {
  console.log(meta)

to see if fatal === true.

Please also include code for your seneca.add call so we can see if this is the case.

How do I throw errors from an action in Seneca?

1 Answers1