Topic 18730 min readStructured Tutorial

JavaScript Projects: Building an Expense Tracker

Quick Answer

An Expense Tracker is a JavaScript project that helps users record and manage their daily expenses. It typically includes features like adding, editing, and deleting expenses, and calculating totals. Building this project teaches fundamental JavaScript concepts such as DOM manipulation, event handling, and local storage.

Learning Objectives

Explain the purpose of Expense Tracker in a practical learning context.
Identify the main ideas, terms, and decisions involved in Expense Tracker.
Apply Expense Tracker in a simple real-world scenario or practice task.

Introduction to the Expense Tracker Project

Building projects is a great way to learn JavaScript by applying concepts in practical scenarios.

An Expense Tracker helps users monitor their spending by recording expenses and calculating totals.

This tutorial will guide you through creating a simple yet functional Expense Tracker using JavaScript.

Code is like humor. When you have to explain it, it’s bad.

Project Overview

The Expense Tracker project allows users to add expenses with descriptions and amounts, view a list of expenses, and see the total spending.

Key features include adding new expenses, deleting existing ones, and persisting data using the browser's local storage.

Add expense with description and amount
Display list of all expenses
Calculate and display total expenses
Delete expenses from the list
Save data in local storage for persistence

Setting Up the Project Structure

Create an HTML file to structure the user interface with input fields and buttons.

Use CSS for basic styling to make the app user-friendly.

Add a JavaScript file to handle the logic and interactivity.

HTML: Input fields for description and amount, add button, expense list container, total display
CSS: Simple layout and spacing
JavaScript: Event listeners, DOM manipulation, local storage handling

Core JavaScript Concepts Used

This project reinforces several important JavaScript concepts essential for web development.

DOM manipulation to update the expense list dynamically
Event handling for user interactions like clicking buttons
Using arrays and objects to store expense data
Local storage API to save and retrieve data persistently
Functions to organize reusable code

Step-by-Step Coding Guide

Let's break down the coding process into manageable steps.

1. Capture user input for description and amount.
2. Validate inputs to ensure description is not empty and amount is a positive number.
3. Create an expense object and add it to an array.
4. Update the expense list in the DOM to display all expenses.
5. Calculate the total expenses and display it.
6. Save the expense array to local storage.
7. Load expenses from local storage when the app starts.
8. Implement delete functionality to remove expenses.

Example: Adding an Expense

Here is a simple example of how to add an expense and update the list.

JavaScript Code Snippet

This code captures input values, creates an expense object, adds it to the array, updates the DOM, and saves to local storage.

Practical Example

This function validates inputs, creates an expense object with a unique id, adds it to the expenses array, saves the array to local storage, updates the UI, and clears input fields.

Examples

Add Expense Function Example

function addExpense(description, amount) {
  if(description === '' || amount <= 0) {
    alert('Please enter valid description and amount');
    return;
  }
  const expense = { id: Date.now(), description, amount: parseFloat(amount) };
  expenses.push(expense);
  saveExpenses();
  renderExpenses();
  clearInputs();
}

This function validates inputs, creates an expense object with a unique id, adds it to the expenses array, saves the array to local storage, updates the UI, and clears input fields.

Best Practices

Validate user inputs to prevent invalid data.
Use unique IDs for each expense to manage deletion easily.
Keep functions small and focused on a single task.
Persist data using local storage for better user experience.
Update the UI dynamically without page reloads.

Common Mistakes

Not validating inputs leading to empty or negative amounts.
Forgetting to update local storage after changes.
Manipulating the DOM inefficiently causing performance issues.
Using global variables unnecessarily.
Not handling edge cases like deleting the last expense.

Hands-on Exercise

Implement Expense Editing

Extend the Expense Tracker to allow editing existing expenses.

Expected output: Users can modify expense descriptions and amounts, and changes persist in local storage.

Hint: Add an edit button for each expense and update the expense object and UI accordingly.

Add Expense Categories

Add a category field to each expense and allow filtering expenses by category.

Expected output: Expenses can be categorized and filtered dynamically.

Hint: Use a dropdown for categories and filter the displayed list based on selection.

Interview Questions

How can you store data persistently in a JavaScript web app without a backend?

Interview

You can use the browser's local storage API to save data persistently on the client side. It allows storing key-value pairs that remain available even after the page is reloaded.

What is event delegation and how can it be useful in an Expense Tracker?

Interview

Event delegation is a technique where a single event listener is added to a parent element to handle events on its child elements. It is useful for dynamically added expense items to manage events like delete clicks efficiently.

What is Expense Tracker, and why is it useful?

Beginner

An Expense Tracker is a JavaScript project that helps users record and manage their daily expenses.