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WebAssembly · 04 Inspecting Exports
Series contents · Technology map
Stage: Modules and Numeric Contracts · External example · preview instructions · Storage ID: webassembly-step-04
Goals and learning outcomes
- Learning outcome: explain the role of Export surface. Input cases: a valid module and a typo in a required name.
- Deliverable: the export list and error guidance. Explain the rationale for handling Contract checks, linking it to the code.
Prerequisites
Prepare the experiment results for Module and Instance from Unit 3, “Compile and Instance”.
Key concepts and explanations
Export surface
JS accesses functions and memory by their public names. Guessing names and types causes runtime failures.
Contract checks
Module.exports lets you inspect public entries. Treat a missing required export as an initialization error.
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-4.mjs in a separate practice project, print Module.exports and check for memory·sum·at·transform. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: a valid module and a typo in a required name. Baseline: sum. Run under the baseline conditions, then record observations and errors in notes/day-4.md.
- Variable: requested name; changed value: sumMissing. Run again through the same input path. Deliverable to save: the export list and error guidance. Hypothesis to check: The missing entry is clearly reported, and computation does not start. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| requested name | sum | sumMissing | The missing entry is clearly reported, and computation does not start. |
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: the export list and error guidance. 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: Export surface and Contract checks. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Export surface affect in this exercise? Input cases: a valid module and a typo in a required name.
- Variable: requested name. Hypothesis to check: The missing entry is clearly reported, and computation does not start. Did the actual results agree with the hypothesis? Explain the evidence in terms of Contract checks.
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: Compile and Instance · Next: Imports and Host Functions