Basic Node and Express

This is the boilerplate code for the Basic Node and Express Challenges. Instructions for working on these challenges start at https://www.freecodecamp.org/learn/apis-and-microservices/basic-node-and-express/

Notes

Request and Response objects

Express has two main objects to work with: req and res.

Request (req)

The req object represents the HTTP request and has properties for the request query string, parameters, body, HTTP headers, and so on. The properties of the req object can be found here

Response (res)

The res object represents the HTTP response that an Express app sends when it gets an HTTP request. The properties of the res object can be found here

serving in Express

Express routes use the following template: app.METHOD(PATH, HANDLER) where:

METHOD is an HTTP method in lowercase
PATH is a relative path on the server (Can be string or regex).
HANDLER is the function Express calls when the route matches.
- HANDLER takes the form of function(req, res) {...}
  - example: app.get("/", (res, req) => {...}) for arrow functions
  - example: app.get("/", function(res, req)) for traditional functions
app.send() allows you to send a string
app.sendFile() allows you to send a file, the headers are automatically applied
app.static(path) where path is the absolute path of the folder containing the asset allows you to call static assets such as stylesheets, scripts and images. This is a middleware function, which are functions that intercept route handlers and add some kind of information. These functions must be mounted using app.use(path, middlewareFunction), the first path is optional. If it is not set, the middleware will be applied to all requests.
- use: app.use(express.static(__dirname + "/path")) and app.use("/path", express.static(__dirname + "/path")) to allow anything in the folder "path" be used when "/path" is mentioned

Serving JSON, REST API

REST stands for REpresentational State Transfer. A REST API allows for data exchange without clients needing to know details about the server itself. All the client will need is the url where the resource is and the action they want to perform on it (ie. GET from localhost:3000/test). (more verbs)

GET - fetch info without modifying anything
POST - submits an entity to the specific resource
PUT - replaces all current representations of the resource with the request payload
DELETE - deletes specific resource
HEAD - asks for a response identical to the GET but without the response body
CONNECT establishes a tunnel to the server identified by the target resource
OPTIONS describes the communication options for the target resource
TRACE performs a message loop-back test along the path to the target resource
PATCH applies partial modifications to a resource

middleware

Middleware functions take 3 arguments, the request object, the response object and the next function in the application's request-response cycle. Meaning the functions execute code that can have side effects on the app, like adding information to the request or response object. They can also end the cycle by sending a response when some condition is met. If they don't send the response when done, they start the execution of the next function in the stack, which is triggered by the 3rd argument next().

function(req, res, next) {
  console.log("I'm a middleware...");
  next();
}

the above middleware function will print the string I'm a middleware... and then executes the next function in the stack, when a request matches the route. You can specify when the middleware has to be used: app.use(middlewareFunction()) for execution at the root level, app.METHOD(middlewareFunction()) if the function should only be executed for a specific method (GET, POST, DELETE etc.).

NHariman / FreeCodeCamp-Node