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Offline-First Notes App ​

DifficultyIntermediate
Team SizeSolo
Time~25-30 hours
Demo-ready byStep 5
PrerequisitesHTML, CSS, JavaScript, browser storage concepts
Built byNotion, Obsidian, Apple Notes, Standard Notes

Skills you'll earn: Service Workers, IndexedDB, PWA architecture, rich text editing, offline-first sync, CRDTs

Start with a text input. End with a syncing, offline-capable notes app.

(Assumes starting from scratch with basic HTML/CSS/JS knowledge)

Step 1: Write and save a note (~1-2 hours) ​

You want to jot something down in the browser and not lose it.

  • One HTML page with a <textarea> and a "Save" button
  • Save the content to localStorage
  • Load it back when the page opens
  • Auto-save on every keystroke (debounced)

You now have: A persistent single note.

Step 2: Multiple notes (~2-3 hours) ​

You want more than one note.

  • Store an array of notes in localStorage, each with an ID, title, body, and timestamp
  • Build a sidebar listing all notes, sorted by last modified
  • Click a note to load it into the editor
  • Add "New Note" and "Delete Note" buttons

You now have: A multi-note editor.

Step 3: Make it a PWA (~2-3 hours) ​

You open the app on the bus. No internet. The page won't load.

  • Add a service worker that caches the app shell (HTML, CSS, JS)
  • Add a manifest.json with app name, icons, and theme color
  • The app now loads from cache when offline
  • Add an "install" prompt so users can add it to their home screen

You now have: An installable offline app.

Step 4: Rich text editing (~3-4 hours) ​

Plain text is limiting. You want headings, bold, lists.

  • Replace the textarea with a rich text editor (Tiptap, Quill, or ContentEditable with commands)
  • Support markdown shortcuts (type # to create a heading)
  • Store content as HTML or a structured document format
  • Keep it fast — no loading spinners for typing

You now have: A rich notes editor.

Step 5: IndexedDB storage (~2-3 hours) ​

localStorage has a 5-10MB limit. You have hundreds of notes with images.

  • Migrate storage to IndexedDB (use a wrapper like Dexie.js or idb)
  • Store notes as structured objects with indexes on title and updatedAt
  • Support storing binary data (images) alongside notes
  • Migration: move existing localStorage notes to IndexedDB on first load

You now have: Scalable local storage.

Step 6: Full-text search (~2-3 hours) ​

You have 200 notes. You can't find the one about "project deadlines."

  • Build a search index over note titles and bodies
  • Use a client-side search library (Lunr.js, MiniSearch, or FlexSearch)
  • Update the index when notes are created or modified
  • Show results ranked by relevance

You now have: Instant search, fully offline.

Step 7: Cloud sync (~4-5 hours) ​

You write on your laptop. You want to read on your phone.

  • Set up a simple sync server with Express and a database
  • Each note has a version or updatedAt timestamp
  • On sync: push local changes to server, pull remote changes
  • Handle conflicts: if both sides changed, keep both versions and let the user pick

You now have: Multi-device sync.

Step 8: Tags and organization (~2-3 hours) ​

  • Add tags to notes
  • Filter the sidebar by tag
  • Add folders or notebooks for hierarchical organization

Step 9: Collaboration (~4-5 hours) ​

  • Share a note via a link
  • Real-time collaborative editing using CRDTs (Yjs or Automerge)
  • Show collaborator cursors

Step 10: Deploy (~2 hours) ​

  • Deploy the PWA to a CDN
  • Deploy the sync server behind TLS
  • Add CI/CD

Useful Resources ​

Where to go from here ​

  • End-to-end encryption (encrypt notes before syncing)
  • Markdown export/import
  • Daily notes and journaling features
  • Web clipper (save content from other pages)
  • Kanban view for task-oriented notes