what is express js

1basic server
2
3const express =require('express');
4const app = express();
5const PORT = 5000;
6
7
8app.get('/',(req,res)=>{
9   res.json({message: 'Welcome to the backend'})
10})
11
12
13app.listen(PORT ,()=>console.log(`Connected to ${PORT}`)
14           
15           

1
2const express = require('express')
3const app = express()
4const port = 3000
5
6app.get('/', (req, res) => {
7  res.send('Hello World!')
8})
9
10app.listen(port, () => {
11  console.log(`Example app listening at http://localhost:${port}`)
12})
13

1$ npm install express --no-save
2

1
2const express = require('express')
3const app = express()
4const port = 3000
5
6app.get('/', (req, res) => {
7  res.send('Hello World!')
8})
9
10app.listen(port, () => {
11  console.log(`Example app listening at http://localhost:${port}`)
12})
13
14

1// node js -> express -> basic example: static folder, 404 page
2
3const express = require('express');
4const path = require('path');
5const PORT = process.env.PORT || 5000;
6
7const app = express();
8
9function error404(req, res) {
10  res.status(404);
11
12  if (req.accepts('html')) {
13    res.sendFile(path.join(__dirname, 'public/errors/404.html'));
14    return;
15  }
16
17  if (req.accepts('json')) {
18    res.send({
19      status: 404,
20      error: 'Not found'
21    });
22    return;
23  }
24  
25  res.type('txt').send('404 - Not found');
26}
27
28app
29  .use(express.static(path.join(__dirname, 'public')))
30  .use(error404)
31  .listen(PORT, () => console.log(`Listening on ${ PORT }`));
32

1const express = require('express');
2const app = express();
3const port = 3000;
4
5app.get('/', (req, res) => {
6  res.send('Hello World!')
7});
8
9app.listen(port, () => {
10  console.log(`App listening at http://localhost:${port}`)
11});