General `NodeJs/express` Error when declaring routes (TypeError: Cannot read property 'length' of undefined at pathtoRegexp)

Question

I'm new at node.js, and this error cost me many efforts of investigations so I'm sharing this.

I've only tried to declare the express and some basic routers in my index.js:

const express = require('express');
const app = express();

app.get('/api/courses', (req, res)=>{
    res.send(courses);
});

app.get('/api/courses:id', (req, res)=>{
    const course = courses.find(c => c.id === parseInt(req.params.id));
    if (!course) res.send('The given id was not found...');
    res.send(course);   
});

app.get();

The error details:

\node_modules\path-to-regexp\index.js:63 path = ('^' + path + (strict ? '' : path[path.length - 1] === '/' ? '?' : '/?')) ^

TypeError: Cannot read property 'length' of undefined at pathtoRegexp (C:\Users...\node_modules\path-to-regexp\index.js:63:49) at new Layer (C:\Users...\node_modules\express\lib\router\layer.js:45:17) at Function.route (C:\Users...\node_modules\express\lib\router\index.js:494:15) at Function.app.(anonymous function) [as get] (C:\Users...\node_modules\express\lib\application.js:481:30) at Object. (C:...\index.js:24:5) at Module._compile (module.js:652:30) at Object.Module._extensions..js (module.js:663:10) at Module.load (module.js:565:32) at tryModuleLoad (module.js:505:12) at Function.Module._load (module.js:497:3)

Answer 1

The reason behind that error is using the app.get() method without param, which expect the endpoint url and call back as parameters.

Answer 2

The app.get(); causes the error.

As the documentation says, the app.get(path, callback [, callback ...]) must have a path argument (also app.get(name) must have name argument).