Money Engine: The Bug That Costs Millions
0.1 plus 0.2 is not 0.3, and that bug has cost real companies real money. Build a money library that does the math correctly, splits bills, and never lies.
What you'll be able to build
0.1 plus 0.2 is not 0.3, and that bug has cost real companies real money. Build a money library that does the math correctly, splits bills, and never lies. Along the way you pick up real, transferable JavaScript skills, not just this one project:
- why floating point breaks money (0.1+0.2)
- BigInt and integer-cents arithmetic
- Intl.NumberFormat for currency display
- remainder distribution algorithms
- guard clauses and input validation
- writing a small, well-tested value-object module
A course like this one
Yours is built from your own placement, so module count and depth will differ. This map shows what a intermediate-level JavaScript learner building Money Engine actually gets.
- Module 1: JavaScript Values and Product State5 lessons
Builds the component state for your money engine.
- Module 2: Arrays, Objects, and Client Data5 lessons
Builds the client data model workflow for your money engine.
- Module 3: Events, Branches, and UI Decisions5 lessons
Builds the event rule that powers your money engine.
- Module 4: Functions, Modules, and Tests5 lessons
Builds the reusable utility function for your money engine.
- Module 5: API Boundaries and Async Thinking5 lessons
Builds the API adapter for your money engine.
- Module 6: Frontend Launch Readiness3 lessons
Builds the release checklist for your money engine.
How the lessons actually work
Every lesson has you predict what a piece of JavaScript code will output before you run it, then run it for real in your browser and fix what you got wrong. Each module ends in a challenge gate with hidden tests, so you can't advance until your code actually works. The course closes with a capstone that assembles everything into Money Engine, and a runnable proof page tied to your own code.
Common questions
How long does the Money Engine: The Bug That Costs Millions course take?
about 7 hours, across 6 modules and 28 lessons, at roughly 15 minutes per lesson. Your own course may run shorter or longer, since it's sized to your placement result, not a fixed template.
Do I need experience?
Some. This is an intermediate-tier JavaScript project, so it assumes you're comfortable with JavaScript basics and pushes past them.
How much does it cost?
$15 one-time, no subscription. The first module is free, so you can see exactly how the course teaches before you pay for the rest.