Learnings.md

Learnings :

1. Might get the following errors in console :

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

To resolve it, look for multiple res.status() being sent from one request. Look for return statements carefully too and handle it appropriately. Or look for conditional logic like if..else blocks.

You can send a response to the client only once when you send more than one time that will generate the error 2. About ExpressJS' request object parts :

1. req.body - Generally used in POST/PUT requests when we need to send data to the server. Remember to use express.json() middleware to parse request body else you'll get an error
2. req.params - These are properties attached to the url i.e named route parameters. You prefix the parameter name with a colon ( : ) when writing your routes.

 app.get('/giraffe/:number', (req, res) => {
     console.log(req.params.number)
 })

 GET  http://localhost:3000/giraffe/1

3. req.query - Mostly used for searching,sorting, filtering, pagination, e.t.c. It written as key=value preceeded by ?. We can add multiple queries using & operator in the URL.

 GET  http://localhost:3000/animals?page=10
 GET  http://localhost:3000/animals?page=10&section=2

 app.get('/animals', ()=>{
     Animals.find(req.query)
     console.log(req.query.page) // 10
 })

3. For data hosted on MongoDB Atlas, MongoDB offers an improved full-text search solution, Atlas Search, which has its own $regex operator.
4. For sorting, using mongoose sort() ref here.
5. Promises .then .catch and aysnc/await are 2 different things for aynshronous behaviouors so one must use any one.
6. Signing JWT token and Verifying it must be done in same manner like the following :

// on login
console.log({ email }); // { email: 'meet@gmail.com' }
const token = jwt.sign({ email }, secret); 

// on verification
const verification = jwt.verify(req.headers.authorization, secret); 
console.log(verification); // { email: 'meet@gmail.com' }
return Developer.findOne({ email: verification.email })

OR the following... but this is avoided since we cant check the token type when using a combined authenticator like roleBasedAuthentication middleware.

console.log(email); // meet@gmail.com
const token = jwt.sign(email, secret); 

// on verification
const verification = jwt.verify(req.headers.authorization, secret); 
console.log(verification); // meet@gmail.com
return Developer.findOne({ email: verification })

API Testing :-

1. Installed packages for testing as dev dependencies.

npm i -D mocha chai supertest nyc

2. Created /test folder.
3. When creating /test folder, try to mimic the folder structure of the project in it.
4. Mocha is gonne look for test folder.
5. Enable mocha in the .eslintrc.js
6. Added test script in package.json and ran npm run test. 1. 2. Also added a script for coverage and can run it through npm run test:cov 3. Be careful in naming and avoid typos.
7. To create a test we use describe() which describes a "suite"(a group of related test cases) with the given 'title' and callback fn containing nested suites.
8. done() function is used to handle asynchronous operations in test cases such as making HTTP requests, interacting with databases, or using timers, it's important to notify the testing framework when the asynchronous operations have completed.
   1. This ensures that the test case doesn't complete prematurely or timeout before the asynchronous operations finish.
   2. It is typically passed as a parameter to the test case function, and it needs to be invoked to signal the completion of the test case.
   3. The testing framework waits for done() to be called before moving on to the next test case or completing the test suite.
   4. If done() is not called at the end of test suite then an error like following can occur.

Error: Timeout of 10000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves.

9. Ensure the URL paths of test cases are started with a slash like /developers otherwise the following error can come :

Error: ECONNREFUSED: Connection refused

10. .only used with decribe.only() will run only that test suite.
11. .skip used with describe.skip() will skip that specific test suite.