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Digital · Guided lesson

Export a portable explicit backup

About 29 minutes · 7 reading + 22 practice and checks
Time includes reading, practice, and questions. Extra videos or further study are optional.
See this course’s project requirements

A fictional local reading-list app with versioned saved data, explicit browser-only wording, validated JSON export/import and corrupt-save recovery tests.

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

What to include

  • Document the exact storage origin and distinguish reload persistence from account synchronization.
  • Retain the validated envelope format and prove an invalid replacement leaves the earlier record intact.
  • Demonstrate a rejected corrupt load and a failed write without silently discarding prior data.
  • Create and inspect an actual JSON export and state its exact contents.
  • Produce a valid/invalid import matrix proving rejected content retains the previous list.
  • Deliver a two-tab observation or truthful unavailable note, alongside the validated backup/recovery project.

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.
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Before you begin

The idea in everyday life

Use the supplied reading.html, reading-store.mjs and test-reading.mjs with the invented title Moon Garden. Serve the folder at http://localhost:8765 using python3 -m http.server 8765 --bind 127.0.0.1.

The idea

An export is a file containing the current memory envelope; it is a separate backup only after the learner keeps the downloaded file.

Follow along

Export a portable explicit backup — original worked practice

An export is a file containing the current memory envelope; it is a separate backup only after the learner keeps the downloaded file.

Use the supplied reading.html, reading-store.mjs and test-reading.mjs with the invented title Moon Garden. Serve the folder at http://localhost:8765 using python3 -m http.server 8765 --bind 127.0.0.1.

  1. 1. Step 1

    Add Moon Garden after recovery, then activate Export backup.

    You should see: A JSON download is offered.

    An export is a file containing the current memory envelope; it is a separate backup only after the learner keeps the downloaded file.

  2. 2. Step 2

    Open fictional-reading-list.json as text and compare version, revision, and title with the page.

    You should see: The file contains the current envelope.

    An export is a file containing the current memory envelope; it is a separate backup only after the learner keeps the downloaded file.

  3. 3. Step 3

    Inspect Blob and object URL creation; the temporary URL is revoked after the download starts.

    You should see: The app creates a local file without uploading it.

    An export is a file containing the current memory envelope; it is a separate backup only after the learner keeps the downloaded file.

  4. 4. Step 4

    Keep the file in the practice folder and document what it contains and omits.

    You should see: A verified backup file and scope note.

    An export is a file containing the current memory envelope; it is a separate backup only after the learner keeps the downloaded file.

Now change one thing

Start with the one-title Moon Garden record. In a valid changed state add River Map and Quiet Library as two different title strings, then export that state. How many title records should the exported items array contain?

Your work

What to finish

Create and inspect an actual JSON export and state its exact contents.

Common mistake

Watch for this

Describing a title-list export as a backup of the original books or documents.

How can I tell I understand it?

Demonstrate the rule: An export is a file containing the current memory envelope; it is a separate backup only after the learner keeps the downloaded file. Use the supplied variant to distinguish a changed result from a broken implementation.

Try 3 questions

Quick knowledge check

Answer all 3 questions. Get at least 2 right and the lesson completes automatically.

Not yet passed

You’ll get an explanation for each answer. Signed in? Your results save to your account.

1What does the reading JSON backup contain?
2What turns the offered download into a usable backup?
3Why revoke the temporary object URL after export?
0 of 3 answeredApply the lesson to a short question, then review the explanation.
4
Finish this lesson

Pass the check. We’ll save the progress.

Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.

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Sources and further reading

Explore the references behind this lesson.

developer.mozilla.org — Blob
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.

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