Express js Route.get() requires a callback function but got a [object Undefined] - express

Question

Attempting to learn Expresss.js via this tutorial and I am at the point of adding routes. I believe I have followed the tutorial exactly, but I am getting this error:
[nodemon] starting `node ./bin/www`
/Users/dariusgoore/development/express-locallibrary-tutorial/node_modules/express/lib/router/route.js:202
throw new Error(msg);
^
Error: Route.get() requires a callback function but got a [object Undefined]
at Route.(anonymous function) [as get] (/Users/dariusgoore/development/express-locallibrary-tutorial/node_modules/express/lib/router/route.js:202:15)
at Function.proto.(anonymous function) [as get] (/Users/dariusgoore/development/express-locallibrary-tutorial/node_modules/express/lib/router/index.js:510:19)
at Object.<anonymous> (/Users/dariusgoore/development/express-locallibrary-tutorial/routes/catalog.js:86:8)
at Module._compile (internal/modules/cjs/loader.js:689:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
at Module.load (internal/modules/cjs/loader.js:599:32)
at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
at Function.Module._load (internal/modules/cjs/loader.js:530:3)
at Module.require (internal/modules/cjs/loader.js:637:17)
at require (internal/modules/cjs/helpers.js:22:18)
at Object.<anonymous> (/Users/dariusgoore/development/express-locallibrary-tutorial/app.js:9:21)
at Module._compile (internal/modules/cjs/loader.js:689:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
at Module.load (internal/modules/cjs/loader.js:599:32)
at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
at Function.Module._load (internal/modules/cjs/loader.js:530:3)
[nodemon] app crashed - waiting for file changes before starting...
Here are the relevant files:
routes/catalog.js
var express = require('express');
var router = express.Router();
// Require controller modules.
var book_controller = require('../controllers/bookController');
var author_controller = require('../controllers/authorController');
var genre_controller = require('../controllers/genreController');
var book_instance_controller = require('../controllers/bookinstanceController');
/// BOOK ROUTES ///
// GET catalog home page.
router.get('/', book_controller.index);
// GET request for creating a Book. NOTE This must come before routes that display Book (uses id).
router.get('/book/create', book_controller.book_create_get);
// POST request for creating Book.
router.post('/book/create', book_controller.book_create_post);
// GET request to delete Book.
router.get('/book/:id/delete', book_controller.book_delete_get);
// POST request to delete Book.
router.post('/book/:id/delete', book_controller.book_delete_post);
// GET request to update Book.
router.get('/book/:id/update', book_controller.book_update_get);
// POST request to update Book.
router.post('/book/:id/update', book_controller.book_update_post);
// GET request for one Book.
router.get('/book/:id', book_controller.book_detail);
// GET request for list of all Book items.
router.get('/books', book_controller.book_list);
/// AUTHOR ROUTES ///
// GET request for creating Author. NOTE This must come before route for id (i.e. display author).
router.get('/author/create', author_controller.author_create_get);
// POST request for creating Author.
router.post('/author/create', author_controller.author_create_post);
// GET request to delete Author.
router.get('/author/:id/delete', author_controller.author_delete_get);
// POST request to delete Author.
router.post('/author/:id/delete', author_controller.author_delete_post);
// GET request to update Author.
router.get('/author/:id/update', author_controller.author_update_get);
// POST request to update Author.
router.post('/author/:id/update', author_controller.author_update_post);
// GET request for one Author.
router.get('/author/:id', author_controller.author_detail);
// GET request for list of all Authors.
router.get('/authors', author_controller.author_list);
/// GENRE ROUTES ///
// GET request for creating a Genre. NOTE This must come before route that displays Genre (uses id).
router.get('/genre/create', genre_controller.genre_create_get);
//POST request for creating Genre.
router.post('/genre/create', genre_controller.genre_create_post);
// GET request to delete Genre.
router.get('/genre/:id/delete', genre_controller.genre_delete_get);
// POST request to delete Genre.
router.post('/genre/:id/delete', genre_controller.genre_delete_post);
// GET request to update Genre.
router.get('/genre/:id/update', genre_controller.genre_update_get);
// POST request to update Genre.
router.post('/genre/:id/update', genre_controller.genre_update_post);
// GET request for one Genre.
router.get('/genre/:id', genre_controller.genre_detail);
// GET request for list of all Genre.
router.get('/genres', genre_controller.genre_list);
/// BOOKINSTANCE ROUTES ///
// GET request for creating a BookInstance. NOTE This must come before route that displays BookInstance (uses id).
router.get('/bookinstance/create', book_instance_controller.bookinstance_create_get);
// POST request for creating BookInstance.
router.post('/bookinstance/create', book_instance_controller.bookinstance_create_post);
// GET request to delete BookInstance.
router.get('/bookinstance/:id/delete', book_instance_controller.bookinstance_delete_get);
// POST request to delete BookInstance.
router.post('/bookinstance/:id/delete', book_instance_controller.bookinstance_delete_post);
// GET request to update BookInstance.
router.get('/bookinstance/:id/update', book_instance_controller.bookinstance_update_get);
// POST request to update BookInstance.
router.post('/bookinstance/:id/update', book_instance_controller.bookinstance_update_post);
// GET request for one BookInstance.
router.get('/bookinstance/:id', book_instance_controller.bookinstance_detail);
// GET request for list of all BookInstance.
router.get('/bookinstances', book_instance_controller.bookinstance_list);
module.exports = router;
in app.js:
var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');
var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');
var catalogRouter = require('./routes/catalog'); //Import routes for "catalog" area of site
var app = express();
//Set up mongoose connection
var mongoose = require('mongoose');
var mongoDB = 'mongodb://dariusgoore:654321cg#ds145704.mlab.com:45704/local_library_dg';
mongoose.connect(mongoDB);
mongoose.Promise = global.Promise;
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'MongoDB connection error:'));
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'pug');
app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use('/', indexRouter);
app.use('/users', usersRouter);
app.use('/catalog', catalogRouter); // Add catalog routes to middleware chain.
// catch 404 and forward to error handler
app.use(function(req, res, next) {
next(createError(404));
});
// error handler
app.use(function(err, req, res, next) {
// set locals, only providing error in development
res.locals.message = err.message;
res.locals.error = req.app.get('env') === 'development' ? err : {};
// render the error page
res.status(err.status || 500);
res.render('error');
});
module.exports = app;
By process of elimination (and referenced in the error trace), the route that is causing the error is this one:
// GET request for one Genre.
router.get('/genre/:id', genre_controller.genre_detail);
Commenting out that route eliminates the error, but I can't tell why.

Answer 1

Figured this out. the controller spelled the action differently.
The router line above references genre_controller.genre_detail
whereas the controller exported genre_details
changing details to detail in the controller solves this issue.