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JavaScript · 23 File Import and Structure Validation

Series contents · Technology map

Stage: Integrating and verifying the experiment log · Editable example · Storage ID: javascript-step-23

Goals and learning outcomes

Prerequisites

The work and experiment records from Unit 22, “Exporting JSON with Blob”

Key concepts and explanations

Reading Files

File.text returns a Promise for a string. A file extension alone cannot establish that its contents are valid.

Atomic Updates

Validate the entire input before replacing state. Prevent an error partway through from overwriting only part of the existing data.

Practice setup

First check the execution scope guidance on the example screen. The following environment is for extending the assignment in a separate project. Implement it yourself in a separate local project and check it with browser developer tools. In a separate folder, connect your practice JS from index.html using script type="module" and open it through a local HTTP server. Use the Console, Network, and Elements panels.

The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.

Practice tasks

  1. In import.js, prepare a valid file and a file whose second title is a number.
  2. Read the file, validate the array, id, and title, and apply only the entire array that passed validation.
  3. Run with a valid file and a file whose second title is a number. Results to check: Restore exactly the number of items in a valid file. The existing id array is unchanged after rejection. Record expected and actual results separately.

Variables to observe

VariableBaselineChangeExpected change / hypothesis
Type of titleStringNumberHypothesis before running: The import will be rejected and the existing list preserved. Keep the other conditions fixed and record the actual result separately after running.

Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.

Completion criteria

Self-check

  1. Why is it risky to modify state during validation?
  2. What policy should handle duplicate id values?

Official references

Linked example and execution scope

Example source · Runtime environments and limits

Compare the editable inputs with actual browser execution results.

Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.

Next learning

Previous: Exporting JSON with Blob · Next: State Transitions and Undo

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