Route.get() requires callback functions but got a "object Undefined"

Make sure that

yourFile.js:

exports.yourFunction = function(a,b){
  //your code
}

matches

app.js

var express = require('express');
var app = express();
var yourModule = require('yourFile');
app.get('/your_path', yourModule.yourFunction);

For me, I ran into this issue when copy pasting a module into another module for testing, needed to change the exports. xxxx at the top of the file

There are two routes for get:

app.get('/', main.index);
todoRouter.get('/',todo.all);

Error: Route.get() requires callback functions but got a [object Undefined] This exception is thrown when route.getdoes not get a callback function. As you have defined todo.all in todo.js file, but it is unable to find main.index. That's why it works once you define main.index file later on in the tutorial.

I got the same error. After debugging, I found that I misspelled the method name that I imported from the controller into the route file. Please check the method name.

In the tutorial the todo.all returns a callback object. This is required for the router.get syntax.

From the documentation:

router.METHOD(path, [callback, ...] callback)

The router.METHOD() methods provide the routing functionality in Express, where METHOD is one of the HTTP methods, such as GET, PUT, POST, and so on, in lowercase. Thus, the actual methods are router.get(), router.post(), router.put(), and so on.

You still need to define the array of callback objects in your todo files so you can access the proper callback object for your router.

You can see from your tutorial that todo.js contains the array of callback objects (this is what you are accessing when you write todo.all):

module.exports = {
    all: function(req, res){
        res.send('All todos')
    },
    viewOne: function(req, res){
        console.log('Viewing ' + req.params.id);
    },
    create: function(req, res){
        console.log('Todo created')
    },
    destroy: function(req, res){
        console.log('Todo deleted')
    },
    edit: function(req, res){
        console.log('Todo ' + req.params.id + ' updated')
    }
};