Building a fullstack Svelt Application with MongoDB

December 30, 2021

Svelte is a new fronted JavaScript approach to building user interfaces. This introduces a new alternative that we can use besides React, Angular, Vue. However, Svelte is a compiler, whereas the other alternatives are frameworks/libraries.

When you build your apps with Svelte, you run the Svelte compiler that automatically goes over your code and files. This creates bundled JavaScript instructions that execute in the DOM at runtime. Instead of using techniques like virtual DOM diffing, Svelte writes code that surgically updates the DOM when the state of your app changes.

With such an amazing frontend technology, connecting to backend services and accessing data from a server will be essential. This guide teaches more about Svelte and how to create a Svelte application with MongoDB.


To follow along with this article, it is helpful to have the following;

  • Postman installed on your computer.
  • MongoDB server installed on your computer.
  • Node.js installed on your computer.
  • Basic knowledge using Postman, Node.js, MongoDB, and Svelte.

Setting up a Node.js backend API with MongoDB

Create a directory in your desired project folder and name it server. Navigate to the server directory using the command;

cd server

Initialize a Node.js application with default configurations;

npm init -y

Below are the packages we need to set up a Node.js MongoDB backend.

  • Express: Fast and easy to work with Node.js framework while creating minimalist servers.
  • Mongoose: Provide MongoDB Object modelling tool for Node.js.
  • Nodemon: A Node.js development library for automatically restarting when adding new code blocks to a Node.js development server.
  • Cors: For enabling cross-origin communication between Svelte client and the Node.js server

Use the following command to install the above-listed Node.js packages.

npm i express mongoose cors
npm i --save-dev nodemon

To use the Nodemon artifacts, we need to modify the package.json file. To do this, add the following script tag in the package.json scripts section,

"dev":"nodemon ./src/server.js"

We will use the command above to run and restart the Node.js server that we will build.

Setting up a primary express Todo server

Create an src directory within your server directory.

mkdir src

Here we will create and set up a Node.js Express server. Inside src, create a server.js file and;

  • Set up a basic Express application as follows;
const express = require('express');
const mongoose = require('mongoose');
const app = express();
const PORT = process.env.PORT || 4000;

// Middleware
app.use(express.urlencoded({ extended: true }));

//Initiate MongoDB and start server
app.listen(PORT, () => {
    mongoose.connect(process.env.MONGODB_URI || 'mongodb://localhost/your_preferred_db_name', { useNewUrlParser: true }).then((response) => {
        console.log(`Connected to MongoDB and server started on PORT ${PORT}`);
    }).catch((err) => {

This snippet will set up an Express application by Initializing Express middleware to parse incoming requests with JSON payloads; It will also initialize a MongoDB connection and start the server on a localhost port. Start your development server by running the command below;

npm run dev

This command will trigger the Nodemon script that we set in the package.json. Any code you add to your server code base will automatically restart without running the NPM server script.

  • Define the Todo schema;
const Schema = mongoose.Schema;
const todoSchema = new Schema({
    title: String,
    description: String,
const Todo = mongoose.model('Todo', todoSchema);
  • Setup a route for getting all todos;
app.get('/api/todos', async (req, res, next) => {
    const todos = await Todo.find();
    return res.json(todos);
  • Setup a route for adding a new todo;'/api/todos', async (req, res, next) => {
    const todo = new Todo(req.body);
    // save todo to database
    return res.json(todo);
  • Setup a route for deleting an existing todo;
// Delete a todo
app.delete('/api/todos', async (req, res, next) => {
    // find todo by id and delete
    await Todo.findByIdAndDelete(;                   

    return res.json({
        message: 'Todo deleted successfully',
        success: true,

Ensure that the development server is still running, then open Postman and send a POST request to http://localhost:4000/api/todos. Then, select Raw at the body’s tab, set JSON as the body format, add the following sample data, and hit Send.

"title":"Coding in JavaScript",
"description":"I am coding in JavaScript"

The response on the Postman Body section should be similar to;


You can also send a GET request to http://localhost:4000/api/todos to fetch the added data.


Setting up a Svelte application

To set up a Svelte application, we will use vite. So, in the project folder (outside the server folder), create a new directory, name it client.

We will create the Svelte backend within this client directory. Then, run the following command to initialize the Svelte application.

npm init vite@latest

This command creates an interactive command interface that will let you create a basic Svelte application. To do so;

  • Enter the project name as svelte-todos-app.
  • Select svelte as the base framework.
  • For the listed variant, select svelte.

This will create a Svelte application within a svelte-todos-app directory. Navigate to your project;

cd svelte-todos-app

Then install the project dependencies using this command;

npm install

Finally, start the Svelte development server by running the following command.

npm run dev

You can access your basic Svelte application on your browser using http://localhost:3000.


Creating Svelte components

We will be writing three Svelte components;

  • Todo: This will be the component that will render the data as passed as a prop from the Todos component.
  • Todos: This will be the component that will retrieve the list of components from the backend and render each through the Todo component.
  • AddTodo: This will be the component that will get the user data through a form and pass it to the backend API.

Go ahead and create Todo.svelte, Todos.svelte, and AddTodo.svelte files inside the lib directory and start setting up your component.

Setting up the Todo component

In the Todo.svelte file, start by creating a prop used to render data.

    export let todo;
    async function deleteTodo(todo) {
const response = await fetch('http://localhost:4000/api/todos/', {
        method: 'DELETE',
    headers: {
        'Content-Type': 'application/json'
    body: JSON.stringify({
        id: todo._id
    const data = await response.json();
        window.location.href = '/';

Then render the data the way we want to display it on a web page.

    <div class="todo-info">
    <div class="todo-actions">
        <button on:click={
            () => deleteTodo(todo)

Finally, add some little CSS styling to arrange the page components.

article {
    width: 100%;
    margin: 10px 5px;
    padding: 10px;
    box-shadow: 0 1px 3px 0 #d4d4d5, 0 0 0 1px #d4d4d5;
    display: flex;
    justify-content: space-between;

.todo-actions button {
    background: #f5f5f5;
    border: 1px solid #d4d4d5;
    border-radius: 3px;
    color: #333;
    cursor: pointer;
    font-size: 14px;
    font-weight: bold;
    padding: 5px 10px;
    text-transform: uppercase;

Setting up the Todos component

In the Todos.svelte file, begin by importing the onMount() method and the Todo component.

import {onMount} from "svelte";
import Todo from "Todo.svelte";
  • Define the variable to hold our todos.
let todos = [];
  • Define an async onMount() function to fetch the todos when the component is rendered.
onMount(async () => {
    await fetch(`http://localhost:4000/api/todos/`)
        .then(r => r.json())
        .then(data => {
            todos = data;

</script >
  • Iterate through each todo retrieved and pass them through as a prop to the Todo component.
{ #if todos }
{ #each todos as todo }
        <Todo {todo} />
{:else }
<p class="loading">loading...</p>
{ /if}

This will check whether the todos data is retrieved, if yes, then we can iterate them over, sending each as a prop to the Todo component. If the data has not been retrieved yet, we show a loading action.

  • Add the following styles.
<style>ul {
    width: 80%;
    margin: 10px auto;
    list-style-type: none;
    padding: 0px;

li {
    display: block

.loading {
    opacity: 0;
    animation: 0.5s 0.6s forwards fade-in;

@keyframes fade-in {
    from {
        opacity: 0;

    to {
        opacity: 1;


Setting up the AddTodo component

This component will provide a form where users will enter new todo details. In AddTodo.svelte file, add a function in the script section to handle onsubmit.

    async function onSubmit(e) {

    // Get the data from the form
    const formData = new FormData(
    const data = { };
    for (let field of formData) {
        const [key, value] = field;
    data[key] = value;    
    // Send data to the API
    await fetch('http://localhost:4000/api/todos/',{
    body: JSON.stringify(data),
        () => {
        // reload current page
        window.location.href = '/';

Then show this form to a web page.

<div class="form-container">
    <form on:submit|preventDefault={onSubmit}>
    <div class="form-group">
            placeholder="Title of todo."
    <div class="form-group">
            placeholder="Todo's description"
    <div class="form-group">
        <button type="submit">Submit</button>
</div >

Finally, add some CSS styling.

<style>.form-container {
    width: 80%;
    margin: 10px auto;

form {
    display: flex;
    justify-content: flex-start;
    width: 100%;

.form-group {
    margin: 10px;
    width: 30%;

.form-group input[type="text"] {
    padding: 10px;

.form-group textarea {
    padding: 10px;

button {
    background: #f5f5f5;
    border: 1px solid #d4d4d5;
    border-radius: 3px;
    color: #333;
    cursor: pointer;
    font-size: 14px;
    font-weight: bold;
    padding: 5px 10px;
    text-transform: uppercase;


Bundling up the components

We will render our application through the main component, App.svelte. Rewrite the App.svelte component as follows;

  import Todos from './lib/Todos.svelte';
  import AddTodo from './lib/AddTodo.svelte';

  <h1>Todo List</h1>
  <AddTodo />
  <Todos />

  main {
    padding: 1rem;
    width: 80%;
    margin: 0px auto;
  h1 {
    text-align: center;

Ensure your development server is up and running and go to http://localhost:3000 to test if the todos application is working.



Svelte is used to build frontend applications like React, Angular, and Vue. There might be a need to connect to a backend server that uses a database such as MongoDB.

This guide helped you build a complete full-stack reactive Svelte-inspired application. I hope that was of assistance to you.

Happy coding!

Peer Review Contributions by: Mercy Meave