Node.js with Express - throw Error vs next(error)

In general express follows the way of passing errors rather than throwing it, for any errors in the program you can pass the error object to 'next' , also an error handler need to be defined so that all the errors passed to next can be handled properly

http://expressjs.com/guide/error-handling.html

Errors that occur in synchronous code inside route handlers and middleware require no extra work. If synchronous code throws an error, then Express will catch and process it. For example:

app.get('/', function (req, res) {
  throw new Error('BROKEN') // Express will catch this on its own.
})

Throwing an error inside a callback doesn't work:

app.get('/', function (req, res) {
  fs.mkdir('.', (err) => {
    if (err) throw err;
  });
});

But calling next works:

app.get('/', function (req, res, next) {
  fs.mkdir('.', (err) => {
    if (err) next(err);
  });
});