Template engine?

before using template engine

const express = require('express');
const app = express()
const port = 3000

app.use(express.urlencoded({extended: false}));
app.use(express.json())

app.use(express.static('public'));  // to offer static files

app.use((req, res, next) => {  // middleware before going to router.
    // console.log(req);  // see all request
    next();  // finish middleware and go to next step.
});

// before using template engine
app.get('/', (req, res) => {
    res.send('<!DOCTYPE html>\\
    <html lang="en">\\
    <head>\\
        <meta charset="UTF-8">\\
        <meta http-equiv="X-UA-Compatible" content="IE=edge">\\
        <meta name="viewport" content="width=device-width, initial-scale=1.0">\\
        <title>Document</title>\\
    </head>\\
    <body>\\
        Hi. I am with html<br>\\
        <a href="/hi">Say Hi!</a>\\
    </body>\\
    </html>')
});

app.listen(port, () => {
    console.log(`Listening at <http://localhost>:${port}`);
})

HTML files will be so long and it's gonna be so messy

Template engine Advantage

Make it short (with simple syntax. simpler than HTML)
Re-using (same design, different data)
Maintenance

To use Template engine

ejs: Embedded JavaScript Templates

npm install ejs

index.js

// using ejs
app.set('views', __dirname + '/views');
app.set('view engine', 'ejs');

app.get('/test', (req, res) => {
    let name = req.query.name;  // ?name=garden

    res.render('test', {name});
})