Project tutorial
JavaScript Calculator
Build a browser calculator in four steps: HTML structure, CSS layout, math logic, then keyboard and accessibility polish.
How this project works
This project walks you through MiniCalc, a four-function calculator that runs entirely in the browser. You will not install Node, React, or any build tools. Each lesson adds one layer—structure, look, behavior, then polish—so you always know why a file exists.
You should already recognize basic HTML tags such as headings, paragraphs, and links. You do not need prior JavaScript experience beyond curiosity. When we introduce variables, events, and the DOM, we explain them in plain language before showing code.
Clone fcc-js-calculator. The repository has numbered folders. Each folder is a complete snapshot of the app at that stage. Open a folder with a local server, click around, then read the matching lesson to understand what changed.
By the end you will have digit entry, addition, subtraction, multiplication, division, clear, backspace, keyboard shortcuts, screen-reader labels, and a friendly message when someone divides by zero. Those pieces are the same ideas behind many interactive web pages.
Work in order from Part 1 through Part 4. Skip ahead only if a later snapshot already matches what you want to study. When something breaks, compare your files to the snapshot for that part rather than guessing.
Start with part 1 Open GitHub repo
Parts in order
Work through the parts in sequence. Each lesson explains the ideas in plain language, then points you to a complete runnable snapshot on GitHub for that stage.
- Part 1: HTML SkeletonMark up a calculator display and button grid with data attributes ready for later scripting.
- Part 2: StylesLink a stylesheet and layout the calculator as a centered grid with a clear display.
- Part 3: LogicWire click handlers so digits, operators, equals, clear, and backspace compute correctly.
- Part 4: PolishAdd keyboard support, ARIA labels, focus styles, and a clear message for divide-by-zero.