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style: format lesson file for controllers
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@fcasibu
fcasibu committed Mar 27, 2024
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117 changes: 59 additions & 58 deletions nodeJS/express/controllers.md
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Original file line number Diff line number Diff line change
Expand Up @@ -87,10 +87,10 @@ Here is an example of a basic middleware:
```js
function myMiddleware(req, res, next) {
// Perform some operations
console.log('Middleware function called');
console.log("Middleware function called");

// Modify the request object
req.customProperty = 'Hello from myMiddleware';
req.customProperty = "Hello from myMiddleware";

// Call the next middleware/route handler
next();
Expand All @@ -113,16 +113,16 @@ The naming conventions for these controllers are usually based on the route hand
// user controller file/ controllers/userController.js

const getUserById = async (req, res) => {
const userId = req.params.id;
const userId = req.params.id;

const user = await someDBQueryToGetUser(userId);
const user = await someDBQueryToGetUser(userId);

if (!user) {
res.status(404).send('User not found');
return;
}
if (!user) {
res.status(404).send("User not found");
return;
}

res.status(200).send(`User found: ${user.name}`);
res.status(200).send(`User found: ${user.name}`);
};
```

Expand Down Expand Up @@ -153,14 +153,14 @@ const getUserById = async (req, res) => {
const user = await someDBQueryToGetUser(userId);

if (!user) {
res.status(404).send('User not found');
res.status(404).send("User not found");
return;
}

res.status(200).send(`User found: ${user.name}`);
} catch (error) {
console.error('Error retrieving user:', error);
res.status(500).send('Internal Server Error');
console.error("Error retrieving user:", error);
res.status(500).send("Internal Server Error");
// or we can call next(error) instead of sending a response here
// Using `next(error)` however will require you to add a global error middleware that will be demonstrated below
}
Expand All @@ -170,20 +170,20 @@ const getUserById = async (req, res) => {
However, this is not exactly a clean solution since eventually, we will have to add the same try/catch block to *all* controllers. There is a package called `express-async-handler` that you can install to hide this bit, it essentially just chains a `catch` to "catch" any errors in the function.

```js
const asyncHandler = require('express-async-handler');
const asyncHandler = require("express-async-handler");

// Any errors that is thrown in this function will automatically be caught and call the `next` function
const getUserById = asyncHandler(async (req, res) => {
const userId = req.params.id;
const userId = req.params.id;

const user = await someDBQueryToGetUser(userId);
const user = await someDBQueryToGetUser(userId);

if (!user) {
res.status(404).send('User not found');
return;
}
if (!user) {
res.status(404).send("User not found");
return;
}

res.status(200).send(`User found: ${user.name}`);
res.status(200).send(`User found: ${user.name}`);
});
```

Expand Down Expand Up @@ -215,12 +215,13 @@ So the way express distinguishes this middleware is again through adding *four p
```js
app.use((req, res, next) => {
throw new Error("OH NO!");
// or next(new Error("OH NO!"));
// or next(new Error("OH NO!"));
});

app.use((err, req, res, next) => {
console.error(err);
res.status(500).send(err.message); // You will see an OH NO! in the page, with a status code of 500 that can be seen in the network tab of the dev tools
console.error(err);
// You will see an OH NO! in the page, with a status code of 500 that can be seen in the network tab of the dev tools
res.status(500).send(err.message);
});
```

Expand All @@ -230,26 +231,26 @@ With the solutions above, the error middleware can only really respond with a `5

```js
class CustomNotFoundError extends Error {
constructor(message) {
super(message);
this.statusCode = 404;
}
constructor(message) {
super(message);
this.statusCode = 404;
}
}
```

We can then use this custom error class and refactor the earlier version of `getUserById` like so:

```js
const getUserById = asyncHandler(async (req, res) => {
const userId = req.params.id;
const userId = req.params.id;

const user = await someDBQueryToGetUser(userId);
const user = await someDBQueryToGetUser(userId);

if (!user) {
throw new CustomNotFoundError("User not found");
}
if (!user) {
throw new CustomNotFoundError("User not found");
}

res.status(200).send(`User found: ${user.name}`);
res.status(200).send(`User found: ${user.name}`);
});
```

Expand All @@ -259,9 +260,9 @@ It will eventually end up in the error middleware where we can also modify:

```js
app.use((err, req, res, next) => {
console.error(err);
// We can now specify the `err.statusCode` that exists in our custom error class and if it does not exist it's probably an internal server error
res.status(err.statusCode || 500).send(err.message);
console.error(err);
// We can now specify the `err.statusCode` that exists in our custom error class and if it does not exist it's probably an internal server error
res.status(err.statusCode || 500).send(err.message);
});
```

Expand All @@ -273,19 +274,19 @@ We've used the `next` function a few times now. But what exactly is it? Well, to

```js
const middleware1 = (req, res, next) => {
console.log('Middleware 1');
console.log("Middleware 1");
next(); // Pass control to the next middleware
};

const middleware2 = (req, res, next) => {
console.log('Middleware 2');
res.send('Response from Middleware 2');
console.log("Middleware 2");
res.send("Response from Middleware 2");
// request-response cycle ends here
};

const middleware3 = (req, res, next) => {
console.log('Middleware 3');
res.send('Response from Middleware 3');
console.log("Middleware 3");
res.send("Response from Middleware 3");
};

app.use(middleware1);
Expand Down Expand Up @@ -316,29 +317,29 @@ Creating a user controller file that contains well-defined responsibilities to h
```js
// user controller file - controllers/userController.js

const asyncHandler = require('express-async-handler');
const asyncHandler = require("express-async-handler");

const getUserById = asyncHandler(async (req, res) => {
const userId = req.params.id;
const userId = req.params.id;

const user = await someDBQueryToGetUser(userId);
const user = await someDBQueryToGetUser(userId);

if (!user) {
throw new CustomNotFoundError("User not found");
}
if (!user) {
throw new CustomNotFoundError("User not found");
}

res.status(200).send(`User found: ${user.name}`);
res.status(200).send(`User found: ${user.name}`);
});

const getUsers = asyncHandler(async (req, res) => {
// code
// code
});

const createUser = asyncHandler(async (req, res) => {
// code
// code
});

module.exports = { getUserById, getUsers }
module.exports = { getUserById, getUsers };
```

Route file for the "User"
Expand All @@ -357,13 +358,13 @@ const router = express.Router();
// will only execute on `/users/` not `/users/a/b/c` for example unless `router.use` is used
// connect your controllers with the route handlers
router.route('/')
.get(userController.getUsers)
.post(userController.createUser)
// You will likely place your validation/authentication middlewares here or perhaps in the controller file, e.g.
// .post(validationMiddleware, userController.createUser)
.get(userController.getUsers)
.post(userController.createUser);
// You will likely place your validation/authentication middlewares here or perhaps in the controller file, e.g.
// .post(validationMiddleware, userController.createUser)

router.route('/:id')
.get(userController.getUserById);
.get(userController.getUserById);

module.exports = router;
```
Expand Down Expand Up @@ -393,8 +394,8 @@ app.use(express.json());
app.use(express.urlencoded({ extended: false }));

app.use((req, res, next) => {
// You can of course also create your own for your own use-case!
next(); // Just make sure to call `next`
// You can of course also create your own for your own use-case!
next(); // Just make sure to call `next`
})

// base mount path is `/users` and will always execute on that specific mount path, and yes including `/users/a/b/c`
Expand Down

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