How to use sweetalert in nodejs?

I have a nodejs code given with html code, I want to show a sweet alert on client side,after process a function in nodejs?.

var express = require('express');
var router = express.Router();
const Swal = require('sweetalert2');

router.post('/add', function(req, res, next) {

    Swal('Hello world!');

});

<!DOCTYPE html>
<html lang="pt_br">
<head>
</head>
<body>
    <h1 class="text-center title-1"> Cad </h1>
    <form action="/add" method="post">
        <input type="submit" value="Save"/>
    </form>
</body>
</html>

Solution

Here's the only way you can show a popup swal

var express = require('express');
var router = express.Router();

router.post('/add', function(req, res, next) {

   res.json("Hello world!")
});


<!DOCTYPE html>
<html lang="pt_br">
<head>
</head>
<body>
    <h1 class="text-center title-1"> Cad </h1>
    <form id="form" action="#" method="post">
        <input type="submit" value="Save"/>
    </form>
</body>
</html>
<script>

//import JQuery from script
//import swal script

$("#form").on("submit", function(e){
e.preventDefault();

$.ajax({
  url: "/add",
  method: "post"
}).done(d=>{
  swal(e.responseJSON);
});
})
</script>