Full stack MERN contact manager with React hooks, context & JWT authentication. Part of my React course on Udemy.

At the time of the course hooks were very new and much of their implementation tried to substitute lifecycle methods with the closest hooks approximation which is understandable, many tutorials and courses early to adopt hooks took this approach. Hooks were very new at the time of recording, as more clearly defined patterns of use have emerged it's clear that hooks require a completely different approach and thought process to lifecycle methods. We need to think in terms of hooks and functions and not lifecycle.

If you are looking for the code you will see in the Udemy course then please check out the originalcoursecode branch of this repository.

If you're looking to fix your course code or wondering why in the course we had to use // eslint-disable-next-line or thought this doesn't feel right ignoring the linting rules, then I urge you to have a read of this post on overreacted by Dan Abramov. It covers a lot more than just useEffect There is also this great article from Kent C. Dodds. And this excellent full explanation of useEffect on the LogRocket blog.

To summarize the issues we faced in the course though, and why we had to use // eslint-disable-next-line at all is that all our data fetching methods are in our context states (AuthState.js and ContactState.js) and passed down to all our components via the context Provider. The problem with this is that every time we update our context state we create a new function. If we include these functions in our useEffect dependency array (as the linter suggests) then each time we fetch data and our reducer runs it updates the context which triggers a re-render (creating a whole set of new functions). The useEffect dependency sees it as a new function and triggers another render which again updates the state when we call the function in our useEffect, which triggers another re-render and so on.... infinite loop of re-rendering. Even though these functions are called the same and do the same thing, in memory they are different functions.

The solution is not to add an empty array and tell the linter to ignore it (trying to make a componentDidMount out of useEffect), but to think in terms of hooks and functions. We should keep our functions pure where possible and take all our data fetching methods out of context state. Take a look at ContactState.js as an example. You will see all of our action creators have been taken out of the context, this gurantees that the functions never change with a update to state and don't need to be added to the dependency array in useEffect. Each function now takes a dispatch argument as the first parameter which is passed in at the time of invocation. We can safely provide the dispatch via our context as react gurantees that a dispatch returned from useReducer is static and won't change. So the dispatch in our context state will not be a problem. Here is our new getContacts function:

export const getContacts = async (dispatch) => {
  try {
    const res = await axios.get('/api/contacts');

    dispatch({
      type: GET_CONTACTS,
      payload: res.data
    });
  } catch (err) {
    dispatch({
      type: CONTACT_ERROR,
      payload: err.response.msg
    });
  }
};

As you can see it takes disptach as the first argument and it is exported as a named export so we can use it.

We also make a new custom hook to easily consume our auth state and dispatch in our components..

export const useContacts = () => {
  const { state, dispatch } = useContext(ContactContext);
  return [state, dispatch];
};

We can then use our new hook like so (example taken from Contacts.js)

Import it along with our methods

import { useContacts, getContacts } from '../../context/contact/ContactState';

Use the hook to get our state and dispatch

const [contactState, contactDispatch] = useContacts();

const { contacts, filtered } = contactState;

And in our useEffect to fetch our users contacts

useEffect(() => {
  getContacts(contactDispatch);
}, [contactDispatch]);

You'll note that we did not need to include getContacts in our dependency array and we get no warnings now. We don't need to include getContacts as it doesn't change, it's the same function used every time.

Ultimately a good rule of thumb when using react context along with hooks would be to not provide functions in your context state, especially if those functions have side effects. The only exception being the dispatch returned from useReducer.

Test your routes in PostMan with the following...

1. Register a new user - POST http://localhost:5000/api/users

   Headers
   key	value
   Content-Type	application/json

Body

{
"name": "Sam Smith",
"email": "[email protected]",
"password": "123456"
}

2. Login a user - POST http://localhost:5000/api/auth

Body

{
"email": "[email protected]",
"password": "123456"
}

3. Get logged in user - GET http://localhost:5000/api/auth

1. Get a users contacts - GET

2. Add a new contact - POST http://localhost:5000/api/contacts

Body

{
"name": "William Williams",
"email": "[email protected]",
"phone": "77575894"
}

3. Update a contact - PUT http://localhost:5000/api/contacts/<CONTACT_ID>

Body

{
"phone": "555555"
}

4. Delete a contact - DELETE http://localhost:5000/api/contacts/<CONTACT_ID>

Install dependencies

npm install
cd client
npm install

Edit your /config/default.json file to include the correct MongoDB URI

npm run dev     # Express & React :3000 & :5000
npm run server  # Express API Only :5000
npm run client  # React Client Only :3000