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Course 278 · Digital course 41

Make a Small Web App Work Offline

Build a localhost reference-card app with an explicit asset cache, offline fallback, visible cache version and a controlled update/cleanup test. Work from supplied original examples and check changed cases.

Before you start

Review Build your first website and the local API/HTTP basics.

Build Your First Website See everything you’ll need

Free download · Original practice data · No external account required. Download the starter pack

What you’ll leave with

A localhost reference-card app with an explicit asset cache, offline fallback, visible cache version and a controlled update/cleanup test.

Start course Start without an account. Sign in to save lesson progress across devices.

Your project

Start with the practice files. Build your project one lesson at a time.

Practice files are free without an account. Sign in to save your project record in My Proof: a description, checklist, and optional work link. Keep the original files in your own app or notebook; saving a project record does not upload them.

  1. Get your materialsDownload practice filesSupplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.
  2. Make your projectView the project checklist Work in your own notebook, document, or software. Use the supplied practice examples when you prefer.
  3. Keep a private recordSave a project record Sign in to save a description and checklist, then return to update them.
Course handbook

Know the route before you begin.

Here’s what you’ll need and what you’ll make. You can return to this guide during any lesson.

Who this is for

Learners ages 14+ and adults ready for the named prerequisite; no employment or private records required.

Prepare before lesson one
  • Review Build your first website and the local API/HTTP basics.
  • Use a current browser with service workers and developer tools, Python 3 for a loopback server, and optional Node.js for policy assertions. No paid tools or accounts required.
  • Use a dedicated fresh origin/folder. Register only the supplied practice worker and clean up only its prefixed caches.
Your final project

Finish with proof you can use.

A localhost reference-card app with an explicit asset cache, offline fallback, visible cache version and a controlled update/cleanup test.

Save a project record in My Proof
See project checklist and review criteria

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • Create an exact cache inventory and a visible list of excluded offline behavior.
  • Record the local secure context and separate worker registration, installation, and page control.
  • Produce cache-entry evidence and a controlled required-asset failure/repair record.
  • Record actual cached reload and failed-network navigation fallback behavior separately.
  • Produce a controlled update/activation record proving the new version and bounded cache cleanup.
  • Deliver source, policy assertions, version evidence, performed browser tests, and scoped cleanup/limits.

Review and revise

Use these criteria to check your work and choose what to improve.

  • The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
  • Normal, boundary and rejected cases are recorded with expected versus observed results.
  • The changed case has a correct explanation and does not rely on hidden state.
  • The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Three ideas to help you along the way
Three useful ideas

The rules behind the steps.

01

State the contract

Name inputs, permitted states and observable outputs before editing the implementation.

02

Preserve the evidence

Keep the actual source, changed input and expected/observed record so someone can repeat the work.

03

Test the boundary

Check a rejection or changed case and distinguish local practice from real service or native-tool behavior.

What do these words mean?
Key words

Key terms worth knowing.

service worker
A worker that can control requests for a scoped origin/path.
cache
Stored request/response entries managed by the browser.
secure context
A context permitted to use powerful browser APIs.
controller
The active worker controlling a document.
fallback
An explicitly selected response when the intended fetch fails.
Your route

6 lessons.
One useful project.

Work in order the first time. Each lesson makes something the next lesson can use.

  1. 1
    Up next

    Choose a bounded offline asset set

    Create an exact cache inventory and a visible list of excluded offline behavior.

  2. 2
    29 min

    Install in a secure local context

    Record the local secure context and separate worker registration, installation, and page control.

  3. 3
    29 min

    Cache resources through promises

    Produce cache-entry evidence and a controlled required-asset failure/repair record.

  4. 4
    29 min

    Separate cached cards from navigation fallback

    Record actual cached reload and failed-network navigation fallback behavior separately.

  5. 5
    29 min

    Update a cache without deleting other apps

    Produce a controlled update/activation record proving the new version and bounded cache cleanup.

  6. 6
    29 min

    Package truthful offline verification

    Deliver source, policy assertions, version evidence, performed browser tests, and scoped cleanup/limits.

Use the tools

Tools to help you practice.

See all tools
ZIP · practice files

Make a Small Web App Work Offline practice files

Supplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.

Text worksheet

Your course project worksheet

A downloadable text worksheet with each lesson’s working output, space for your answers, and the shared final-project checklist. Save your own copy.

Source transparency

Sources and further study.

Explore the references behind the lessons and take your learning further. Source notes explain access and reuse.

developer.mozilla.org — Service_Worker_API
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

developer.mozilla.org — Cache
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

developer.mozilla.org — Secure_Contexts
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

Ready when you are

Start with the first useful move.

You’ll always know what to do, what to make, and where to go next.

Start lesson one