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Web Workers · 06 Error Response Contracts
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Stage: Messages and Execution Contexts · Editable example · Storage ID: web-workers-step-06
Goals and learning outcomes
- Learning outcome: explain the role of Task errors. Input cases: 0, negative sizes, and sizes above the allowed limit.
- Deliverable: per-request states and pending size. Explain the rationale for handling Cleanup, linking it to the code.
Prerequisites
Prepare the experiment results for View and Offset from Unit 5, “TypedArray and Buffer”.
Key concepts and explanations
Task errors
A computation exception is a failure of an individual request. Distinguish it from a Worker loading or runtime error.
Cleanup
Remove failed requests from the pending list as well. Other valid requests can continue to be processed.
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-6.js in a separate practice project, create an error response containing requestId in try/catch and clean up the main-side pending list. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: 0, negative sizes, and sizes above the allowed limit. Baseline: Within the allowed range. Run under the baseline conditions, then record observations and errors in notes/day-6.md.
- Variable: Size; changed value: Above the upper limit. Run again through the same input path. Deliverable to save: per-request states and pending size. Hypothesis to check: No pending entry remains after failure. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Size | Within the allowed range | Above the upper limit | No pending entry remains after failure. |
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: per-request states and pending size. 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: Task errors and Cleanup. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Task errors affect in this exercise? Input cases: 0, negative sizes, and sizes above the allowed limit.
- Variable: Size. Hypothesis to check: No pending entry remains after failure. Did the actual results agree with the hypothesis? Explain the evidence in terms of Cleanup.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Error Response Contracts experiment with cleanup of the resources it uses.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.
Next learning
Previous: TypedArray and Buffer · Next: Observing Main-Thread Responsiveness