Lesson 14 of 16
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Putting Everything Together to Build a Web App Using JavaScript

Now that you’ve learned the fundamentals of JavaScript, it’s time to put everything together and build a web app. In this final chapter of the “Learn JavaScript” course, you’ll learn how to use JavaScript to build interactive, dynamic web applications that can communicate with servers, access data, and perform complex tasks.

Setting up a Development Environment

Before you start building your web app, you’ll need to set up a development environment. This includes installing a code editor, setting up a local development server, and configuring your project structure.

There are many code editors to choose from, such as Sublime Text, Atom, and Visual Studio Code. These code editors provide features such as syntax highlighting, code completion, and debugging tools to make it easier to write and debug your code.

To set up a local development server, you can use tools such as XAMPP, WAMP, or MAMP. These tools allow you to run a web server on your local machine, which is useful for testing and debugging your web app before deploying it to a live server.

Once you have a code editor and development server set up, you’ll need to decide on a project structure for your web app. A common structure is to have a css directory for your stylesheets, a js directory for your JavaScript files, and an index.html file for your HTML. You may also want to include directories for images, fonts, and other assets.

Building the HTML Structure

The first step in building a web app is to create the HTML structure. This includes defining the layout of your app, adding elements such as headers, footers, and navigation, and marking up the content with HTML tags.

To create the layout of your app, you can use HTML5 structural tags such as header, footer, and main. You can also use CSS to style your app and define the layout using layout properties such as display, flexbox, and grid.

To add navigation to your app, you can use an unordered list with li elements and a nav element. You can also use a button element or a select element to create a dropdown menu.

To mark up your content, you can use a variety of HTML tags such as h1, p, a, and img. You can also use semantic HTML tags such as article, section, and aside to give meaning to your content and make it more accessible to screen readers and search engines.

Adding Interactivity with JavaScript

Once you have the HTML structure of your web app in place, you can start adding interactivity with JavaScript. This includes responding to user events such as clicks, hover, and form submissions, manipulating the DOM to change the content and layout of your app, and making AJAX requests to access data from external sources.

To respond to user events, you can use event listeners such as click, hover, and submit. You can also use the addEventListener method to attach event listeners to elements in your HTML.

To manipulate the DOM, you can use JavaScript methods such as getElementById, querySelector, and createElement to access and modify elements in your HTML. You can use properties such as innerHTML, style, and classList to change the content and appearance of elements, and you can use methods such as appendChild and removeChild to add and remove elements from the DOM.

To make AJAX requests, you can use the fetch function or the XMLHttpRequest object to send HTTP requests to external servers. You can use these requests to access data from APIs, load content from other pages, or submit form data to the server.

Putting it all Together

To build a complete web app, you’ll need to combine all of these elements and use them to create a cohesive, interactive user experience. This may involve using HTML and CSS to design a user interface, using JavaScript to add interactivity and functionality, and using AJAX to access data and communicate with servers.

To test and debug your web app, you can use the development tools in your code editor and browser to inspect the HTML, CSS, and JavaScript, and to identify and fix errors. You can also use console.log statements to output debug messages and test your code.


Building a web app requires a combination of HTML, CSS, and JavaScript skills. By following the steps outlined in this chapter, you should have a solid foundation for building your own web app using JavaScript. Whether you’re creating a simple to-do list app or a complex web application, the concepts and techniques covered in this course will serve as a useful starting point.

Example Project

For this sample project, we’ll build a simple to-do list app using HTML, CSS, and JavaScript. The app will allow users to add, remove, and mark tasks as complete.

To get started, we’ll set up the HTML structure of the app. We’ll create a div element with an id of “todo-list” to contain the list of tasks, and we’ll create a form element with an id of “add-task-form” to allow users to add new tasks. Inside the form, we’ll add a input element with a type of “text” to allow users to enter the task title, and a button element with a type of “submit” to submit the form.

<div id="todo-list">

<form id="add-task-form">
  <input type="text" id="task-title" placeholder="Enter task title">
  <button type="submit">Add Task</button>

Next, we’ll write the CSS to style the app. We’ll use a combination of layout properties such as display and flexbox to define the layout of the app, and we’ll use color and font properties to style the elements.

#todo-list {
  display: flex;
  flex-direction: column;
  width: 400px;
  margin: 0 auto;

#add-task-form {
  display: flex;
  align-items: center;
  margin-bottom: 20px;

#add-task-form input[type="text"] {
  flex-grow: 1;
  padding: 8px;
  font-size: 16px;
  border: none;
  border-radius: 4px;

#add-task-form button[type="submit"] {
  margin-left: 10px;
  padding: 8px;
  font-size: 16px;
  background-color: #00b8d4;
  color: white;
  border: none;
  border-radius: 4px;
  cursor: pointer;

#todo-list ul {
  list-style: none;
  margin: 0;
  padding: 0;

#todo-list li {
  display: flex;
  align-items: center;
  padding: 8px;
  border-radius: 4px;
  margin-bottom: 8px;
  background-color: #f1f1f1;

#todo-list li.completed {
  background-color: #ccc;
  text-decoration: line-through;

#todo-list li .task-title {
  flex-grow: 1;
  font-size: 16px;

#todo-list li .delete-button {
  margin-left: 10px;
  font-size: 16px;
  color: #ff6b6b;
  cursor: pointer;

Finally, we’ll write the JavaScript to add the interactivity to the app. We’ll use the `addEventListener` method to attach event listeners to the form and the delete buttons, and we’ll use DOM manipulation methods to add, remove, and modify elements in the HTML.

// Get references to the form and list elements
const form = document.querySelector("#add-task-form");
const taskList = document.querySelector("#todo-list ul");

// Add a submit event listener to the form
form.addEventListener("submit", e => {
  // Prevent the form from submitting

  // Get the task title from the input element
  const taskTitle = document.querySelector("#task-title").value;

  // Create a new list item element
  const taskItem = document.createElement("li");

  // Add a class of "completed" if the task is completed

  // Set the innerHTML of the task item to the task title
  taskItem.innerHTML = `
    <span class="task-title">${taskTitle}</span>
    <button class="delete-button">Delete</button>

  // Append the task item to the task list

  // Clear the task title input
  document.querySelector("#task-title").value = "";

// Add a click event listener to the task list
taskList.addEventListener("click", e => {
  // Get the target element that was clicked
  const target = e.target;

  // If the target is a delete button, delete the task
  if (target.classList.contains("delete-button")) {

  // If the target is the task title, toggle the completed class
  if (target.classList.contains("task-title")) {

With these HTML, CSS, and JavaScript pieces in place, we now have a functioning to-do list app that allows users to add, remove, and mark tasks as complete.