/
🟩

Introducing to Express

NodeJS
Table of contents

What is Express?

Express is a package for building API and a very popular package.

Install

Terminal
npm i express

Build First Web Server

JS
const express = require('express')
const app = express()
app.get('/', (req, res) => {
    res.send("hello")
});
app.get('/api/courses', (req, res) => {
    res.send([1, 2, 3])
})
app.listen(3000, () => console.log("Server is Running ..."))

Note

We can seprate routes in other file for example '/api/courses' is route and we can save all route about courses in course.js

Use nodemon

When we want to make change in code and don't restart server manually use nodemon package

Terminal
sudo npm i -g nodemon

For now on we use below command to run node application

Terminal
nodemon app.js

Route Parameters

When we want to work with specific data we use parameters in route for example get course with id equal 1, we should pass parameters in route.

JS
const express = require('express')
const app = express()
app.get('/api/courses/:id', (req, res) => {
    res.send(req.params.id)
});
const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Server is Running on ${port} ...`))

Or we can have multiple parameters in route

JS
const express = require('express')
const app = express()
app.get('/api/courses/:year/:month', (req, res) => {
    res.send(req.params)
});
const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Server is Running on ${port} ...`))

For request localhost:5000/api/courses/2020/3 we have below output

Output
{
    year:2020,
    month:3
}

Note

We can pass query string in route after '?'. For example localhost:5000/api/courses/2020/3?sortBy=name Pay attention it's not a new route it's a query string that append in the last of the URL We access query with req.query.

Handling Http GET Requests

JS
const express = require('express')
const app = express()
const courses = [
    { id: 1, course: "course1" },
    { id: 2, course: "course2" },
    { id: 3, course: "course3" },
]
app.get('/api/courses/:id', (req, res) => {
    const course = courses.find(item => item.id === parseInt(req.params.id))
    if (!course) return res.status(404).send("Course Not Found")
    res.send(course)
});
const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Server is Running on ${port} ...`))

Handling Http POST Requests

JS
const express = require('express')
const app = express()
app.use(express.json()) // add middelware
const courses = [
    { id: 1, course: "course1" },
    { id: 2, course: "course2" },
    { id: 3, course: "course3" },
]
app.post('/api/courses', (req, res) => {
    const couse = {
        id: courses.length + 1,
        name: req.body.name
    }
    courses.push(couse)
    res.send(couse)
})
const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Server is Running on ${port} ...`))

Input Validation With Joi

We want to validate data that recive from client and get back response. For validate input We use Joi package. First we create schema to Joi understand the data structure then we use validate function to validate input data

JS
const Joi = require('joi')
const express = require('express')
const app = express()
app.use(express.json())
const courses = [
    { id: 1, course: "course1" },
    { id: 2, course: "course2" },
    { id: 3, course: "course3" },
]
app.post('/api/courses', (req, res) => {
    const schema = Joi.object({
        name: Joi.string().min(3).required()
    })
    const result = schema.validate(req.body)
    if (result.error) { // at same time on of the error or value is null
        return res.status(400).send(result.error.details[0].message)
    }
    const couse = {
        id: courses.length + 1,
        name: req.body.name
    }
    courses.push(couse)
    res.send(couse)
})
const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Server is Running on ${port} ...`))

Handling Http PUT Requests

JS
const Joi = require('joi')
const express = require('express')
const app = express()
app.use(express.json())
const courses = [
    { id: 1, course: "course1" },
    { id: 2, course: "course2" },
    { id: 3, course: "course3" },
]
app.post('/api/courses', (req, res) => {
    const result = validateCourse(req.body)
    // const { error } = validateCourse(req.body) --> Destructuring Object
    if (result.error) return res.status(400).send(result.error.details[0].message)
    // if (error)  return res.status(400).send(result.error.details[0].message)
    if (result.error) return res.status(400).send(result.error.details[0].message)
    const couse = {
        id: courses.length + 1,
        course: req.body.course
    }
    courses.push(couse)
    res.send(couse)
})
app.put('/api/courses/:id', (req, res) => {
    const course = courses.find(item => item.id === parseInt(req.params.id))
    if (!course) return res.status(404).send("Course Not Found")
    const result = validateCourse(req.body)
    // const { error } = validateCourse(req.body) --> Destructuring Object
    if (result.error) return res.status(400).send(result.error.details[0].message)
    // if (error)  return res.status(400).send(result.error.details[0].message)
    course.course = req.body.course
    res.send(course)
})
function validateCourse(course) {
    const schema = Joi.object({
        course: Joi.string().min(3).required()
    })
    return schema.validate(course)
}
const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Server is Running on ${port} ...`))

Handling Http DELETE Requests

JS
const Joi = require('joi')
const express = require('express')
const app = express()
app.use(express.json())
const courses = [
    { id: 1, course: "course1" },
    { id: 2, course: "course2" },
    { id: 3, course: "course3" },
]
app.delete('/api/courses/:id', (req, res) => {
    const course = courses.find(item => item.id === parseInt(req.params.id))
    if (!course) return res.status(404).send("Course Not Found")
    const index = courses.indexOf(course)
    courses.splice(index, 1)
    res.send(course)
})
const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Server is Running on ${port} ...`))
Edit this page
logo
Hi Mohsen save your notes