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Author: Tianle Yuan

** Backend Routing**⚓︎

Definiton⚓︎

When? (background)

client requests to a particular endpoint [ <=> URI + HTTP request method (GET, POST, ...) ].

What? (import routing)

To handle the request, in backend routing, the server handles every request by responding to the client with a code 201(I got that thing you want!) or a 404(Nope, I don’t have that!).

Situation? (example)

Let’s say a user fills out a form with his name, address, favorite hobby and sends a POST request by submitting the form. That GET request url is sent to the server, and the server serves back the requested url to the client as a static file that is stored on the server.

If the server doesn’t have the requested file, then it returns a 404 response error.

Usage⚓︎

Code using
Express.js syntax

app.METHOD(PATH, HANDLER)

  • app: an instance of express.
  • METHOD: an HTTP request method, in lowercase.
  • PATH: a path on the server.
  • HANDLER: the function executed when the route is matched.
Example code 

//Respond with Hello World! on the homepage:
app.get('/', (req, res) => {
    res.send('Hello World!')
})


//Respond to POST request on the root route (/), the application’s home page:
app.post('/', (req, res) => {
    res.send('Got a POST request')
})


//Respond to a PUT request to the /user route:
app.put('/user', (req, res) => {
    res.send('Got a PUT request at /user')
})


//Respond to a DELETE request to the /user route:
app.delete('/user', (req, res) => {
    res.send('Got a DELETE request at /user')
})

Handlers for Routing⚓︎

Open the boxes below to see the examples 👇

Four classes of handler
1° A single callback function can handle a route 

const express = require('express')
const app = express()
const port = 3000
 
app.get('/', (req, res) => {
    res.send('Hello from A!')
})
 
app.listen(port, () => {
    console.log(`Example app listening on port ${port}`)
})

2° More than one callback function can handle a route (use next() to control the next callback.) 

const express = require('express')
const app = express() 
const port = 3000
 
app.get('/', (req, res, next) => {
    console.log('the response will be sent by the next function ...')
    next()
}, (req, res) => {
    res.send('Hello from B!')
})
 
app.listen(port, () => {
    console.log(`Example app listening on port ${port}`)
})

3° An array of callback functions can handle a route 

const express = require('express')
const app = express()
const port = 3000
 
const cb0 = function (req, res, next) {
    console.log('CB0')
    next()
}
 
const cb1 = function (req, res, next) {
    console.log('CB1')
    next()
}
 
const cb2 = function (req, res) {
    res.send('Hello from C!')
}
 
app.get('/', [cb0, cb1, cb2])
 
app.listen(port, () => {
    console.log(`Example app listening on port ${port}`)
})

4° A combination of independent functions and arrays of functions can handle a route 

const express = require('express')
const app = express()
const port = 3000
 
const cb0 = function (req, res, next) {
  console.log('CB0')
  next()
}
 
const cb1 = function (req, res, next) {
  console.log('CB1')
  next()
}
 
app.get('/', [cb0, cb1], (req, res, next) => {
  console.log('the response will be sent by the next function ...')
  next()
}, (req, res) => {
  res.send('Hello from D!')
})
 
app.listen(port, () => {
    console.log(`Example app listening on port ${port}`)
})

References:⚓︎

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