How to Build a Text Compare Tool with HTML, CSS, and JavaScript

Have you ever tried to spot the differences between two long paragraphs of text? Reading line-by-line to find a missing word or a new sentence is a massive headache.

In this tutorial, you’ll build your very own browser-based Text Compare Tool. It will take an original piece of text, compare it against a changed version, and instantly highlight exactly what was added or removed.

Building this project will help you level up your JavaScript skills. You’ll also create a tool that’s highly secure, because everything happens locally in the user’s browser. No sensitive data is ever sent to a server.

Let’s get started.

Prerequisites

To follow along easily, you should know:

• Basic HTML and CSS knowledge: How to structure a page and use Flexbox to put items side-by-side.

• Basic JavaScript knowledge: How to write functions, use arrays, and listen for button clicks.

• Your Setup: A code editor (like VS Code) and a web browser to view your work.

Table of Contents

Step 1: Set Up Your Project Files

First, you need a place to store your code. Create a new folder on your computer and name it text-compare-tool.

Inside that folder, create three empty files:

• index.html (This holds the structure of your app)

• style.css (This makes your app look good)

• script.js (This makes your app actually work)

Step 2: Build the HTML Structure

Open your index.html file. You need to create a simple layout with two large text boxes: one for the original text, and one for the updated text.

Copy and paste this code into your HTML file:

    
    
    
    



    
    

        Quickly find every addition and deletion between two versions of your text. Just paste them into our tool, and we’ll show you exactly what’s been changed.