Devlog 3 — Persistence and Control (File-based History + Clear Command)

What I learned:

Why CLI programs reset completely every time they are executed
How to use the fs module to write and read files in Node.js
How appendFileSync can be used to store data incrementally
How to read stored data using readFileSync
The difference between in-memory state and persistent state
How small bugs (like variable naming or extra trims) can break logic in subtle ways
Why validation, execution and side effects (like saving history) should stay separated

Biggest struggle:

This part was less chaotic than Day 2 but still frustrating in a different way.

The logic itself wasn’t the problem this time. It was understanding how programs behave over time. I had already built a history system before so seeing it disappear every run was confusing at first.

Then came the file system part. Writing to a file felt simple but reading it back properly and formatting it without breaking things took more effort than expected. Small mistakes like misnaming variables or structuring loops incorrectly kept causing issues.

It wasn’t overwhelming chaos but more like constant small friction that slowed everything down.

Current features:

Persistent history system using fs
Calculations are stored in history.txt across runs
history command displays formatted past calculations
clear command wipes stored history clean
Improved validation and error messages
Clean separation between parsing, validation and execution

Next steps:

Convert the calculator into an interactive CLI (REPL-style)
Reduce repeated validation logic into reusable helpers
Improve overall UX (cleaner outputs and command feedback)

Reflection:

The biggest realization was understanding that programs don’t remember anything unless you explicitly store it. That changed how I think about state completely.

Compared to earlier struggles, this one felt quieter but still tiring. Less confusion, more persistence. Fixing small issues, understanding behavior and slowly making things more stable.

It still isn’t perfect but it finally feels like the calculator has some sense of continuity instead of resetting every time.

Note: The screenshot does not show all features (full validation system).