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WebAssembly · 20 Reusing Initialization
Series contents · Technology map
Stage: Deployment and Execution Structure · External example · preview instructions · Storage ID: webassembly-step-20
Goals and learning outcomes
- Learning outcome: explain the role of Initialization cost. Input cases: 5 consecutive requests.
- Deliverable: initialization counts and per-request results. Explain the rationale for handling Concurrent requests, linking it to the code.
Prerequisites
Prepare the experiment results for Streaming and Failure classification from Unit 19, “Browser Loading and MIME”.
Key concepts and explanations
Initialization cost
Compiling for every request incurs repeated costs. You can reuse a module or initialization Promise.
Concurrent requests
Concurrent writes to the same instance's memory mix results. Serialize requests or use separate instances.
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 iframe preview is an experiment with WebAssembly.Memory and JS reference computations; do not present it as execution of an actual Wasm module. Practice with actual modules in a separate Node 22+ environment or a controlled local web project. Use kernel.wat·kernel.wasm·benchmark.mjs in the existing src/labs/webassembly-02·03 folders, and rebuild with the official wat2wasm tool when modifying WAT. Preserve CSP·isolation, and record measurements 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 day-20.mjs in a separate practice project, create a single initialization Promise and a request queue, and count compile calls. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: 5 consecutive requests. Baseline: initialize for every request. Run under the baseline conditions, then record observations and errors in notes/day-20.md.
- Variable: reuse; changed value: share a Promise. Run again through the same input path. Deliverable to save: initialization counts and per-request results. Hypothesis to check: Initialization happens once, and each request's result is correct. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| reuse | initialize for every request | share a Promise | Initialization happens once, and each request's result is correct. |
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: initialization counts and per-request results. 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: Initialization cost and Concurrent requests. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Initialization cost affect in this exercise? Input cases: 5 consecutive requests.
- Variable: reuse. Hypothesis to check: Initialization happens once, and each request's result is correct. Did the actual results agree with the hypothesis? Explain the evidence in terms of Concurrent requests.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
Standalone WAT + Node assertions; iframe CSP blocks Wasm compilation.
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