Open code, practice, and notes →
Download source with English comments · for reading
WebAssembly · 22 Module Caching and Versions
Series contents · Technology map
Stage: Correctness and Bottleneck Evaluation · External example · preview instructions · Storage ID: webassembly-step-22
Goals and learning outcomes
- Learning outcome: explain the role of Cache. Input cases: the correct version and a stale binary.
- Deliverable: source hashes·binary hashes·check results. Explain the rationale for handling Version, linking it to the code.
Prerequisites
Prepare the experiment results for Execution location and Transfer cost from Unit 21, “Workers and Wasm”.
Key concepts and explanations
Cache
Reusing a compiled module can reduce preparation costs. Using an old binary after a source change invalidates verification.
Version
Record source·binary·build-tool versions together. An identical file name does not imply identical code.
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-22.mjs in a separate practice project, add module version metadata to a separate app and inspect exports after the build. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: the correct version and a stale binary. Baseline: new build. Run under the baseline conditions, then record observations and errors in notes/day-22.md.
- Variable: binary; changed value: previous build. Run again through the same input path. Deliverable to save: source hashes·binary hashes·check results. Hypothesis to check: A version mismatch is detected and excluded from the comparison. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| binary | new build | previous build | A version mismatch is detected and excluded from the comparison. |
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: source hashes·binary hashes·check 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: Cache and Version. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Cache affect in this exercise? Input cases: the correct version and a stale binary.
- Variable: binary. Hypothesis to check: A version mismatch is detected and excluded from the comparison. Did the actual results agree with the hypothesis? Explain the evidence in terms of Version.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
Standalone WAT + Node assertions; iframe CSP blocks Wasm compilation.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.
Next learning
Previous: Workers and Wasm · Next: Breaking Down Cold Execution