Open code, practice, and notes →
Download source with English comments · for reading
Web Workers · 02 Module Worker Loading
Series contents · Technology map
Stage: Messages and Execution Contexts · Editable example · Storage ID: web-workers-step-02
Goals and learning outcomes
- Learning outcome: explain the role of Module Worker. Input cases: a valid path and a missing path.
- Deliverable: a ready state or loading error state. Explain the rationale for handling Loading failure, linking it to the code.
Prerequisites
Prepare the experiment results for Worker context and Request identification from Unit 1, “Messages and Execution Boundaries”.
Key concepts and explanations
Module Worker
type:module uses module syntax. Local HTTP and a correct URL are required.
Loading failure
A script path failure differs from a computation error. Show initialization failures as a distinct UI state.
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-2.js in a separate practice project, configure new Worker(new URL('./worker.js',import.meta.url),{type:'module'}) and error handling. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: a valid path and a missing path. Baseline: Valid. Run under the baseline conditions, then record observations and errors in notes/day-2.md.
- Variable: File path; changed value: Nonexistent. Run again through the same input path. Deliverable to save: a ready state or loading error state. Hypothesis to check: An error is displayed instead of leaving the UI waiting for a result. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| File path | Valid | Nonexistent | An error is displayed instead of leaving the UI waiting for a result. |
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: a ready state or loading error state. 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: Module Worker and Loading failure. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Module Worker affect in this exercise? Input cases: a valid path and a missing path.
- Variable: File path. Hypothesis to check: An error is displayed instead of leaving the UI waiting for a result. Did the actual results agree with the hypothesis? Explain the evidence in terms of Loading failure.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Module Worker Loading 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: Messages and Execution Boundaries · Next: Message Contracts