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Web Workers · 04 Structured Clone
Series contents · Technology map
Stage: Messages and Execution Contexts · Editable example · Storage ID: web-workers-step-04
Goals and learning outcomes
- Learning outcome: explain the role of Copying. Input cases: an object and a function field.
- Deliverable: sent and received values and a DataCloneError record. Explain the rationale for handling Cloning limitations, linking it to the code.
Prerequisites
Prepare the experiment results for Tags and Validation from Unit 3, “Message Contracts”.
Key concepts and explanations
Copying
Ordinary objects sent with postMessage are structured-cloned. Changing the object after sending it does not change the separate received object.
Cloning limitations
Functions and DOM nodes cannot be cloned in ordinary messages. Handle failures at the sending stage.
Practice setup
First check the execution scope guidance on the example screen. The following describes the environment needed to extend the assignment in a separate project. The existing web-workers-01·02·03 are starting examples. Implement the new assignments in main.js and worker.js in a separate local HTTP project. Preserve CSP and iframe isolation. For SharedArrayBuffer, check COOP and COEP requirements on an external server you control; use the transfer path if they are not met. Measure performance yourself.
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
- In src/day-4.js in a separate practice project, send a nested object, modify the original afterward, and also try a message containing a function. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: an object and a function field. Baseline: Number. Run under the baseline conditions, then record observations and errors in notes/day-4.md.
- Variable: Field; changed value: Function. Run again through the same input path. Deliverable to save: sent and received values and a DataCloneError record. Hypothesis to check: Values that cannot be cloned are handled separately as sending errors. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Field | Number | Function | Values that cannot be cloned are handled separately as sending errors. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- Required deliverable: sent and received values and a DataCloneError record. Results are available for both the baseline and changed conditions, allowing comparison of 2 conditions; input values and the execution environment are recorded together.
- The explanation of differences between the two conditions connects both concepts: Copying and Cloning limitations. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Copying affect in this exercise? Input cases: an object and a function field.
- Variable: Field. Hypothesis to check: Values that cannot be cloned are handled separately as sending errors. Did the actual results agree with the hypothesis? Explain the evidence in terms of Cloning limitations.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
Interactive Structured Clone experiment with resource cleanup.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.