Clean code & modules

Build a practical mental model for clean code & modules and use it in working JavaScript.

By the end, you will be able to…

Explain clean code & modules in your own words
Use clean code & modules in a small program
Recognize and debug a common failure mode

Build the mental model

Clean code favors small functions and modules with one clear responsibility, descriptive names over comments explaining unclear ones, and consistent structure across a codebase.

Syntax and working example

Read the code from inputs to output. Predict what it prints, then run it and change one value.

Working example

Console

Run your code · Ctrl/⌘ + Enter

Expected output: Smaller, independently readable and testable files

Why this matters

Code is read far more often than it's written; clarity now saves hours of confusion for you or a teammate later.

Real-world example

Code review comments like 'can you extract this into its own function?' are this principle being applied in a real team.

Common mistakes

Writing one giant function that does five unrelated things
Naming things generically (data, temp, handleStuff) instead of descriptively
Duplicating logic in multiple places instead of extracting one shared function

Try it yourself

Challenge

Split calculateOrder into two smaller, named functions: one for the subtotal, one for tax.

Practice

Console

Run your code · Ctrl/⌘ + Enter

Knowledge check

What is a strong signal a function should be split into smaller ones?

Summary

Keep functions and modules small and single-purpose, with descriptive names that reduce the need for comments.