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WebAssembly · 13 Scalar and Batch Calls
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Stage: Memory and Array Boundaries · External example · preview instructions · Storage ID: webassembly-step-13
Goals and learning outcomes
- Learning outcome: explain the role of Call count. Input cases: 100 and 100003 integers.
- Deliverable: call counts·sums·measured times. Explain the rationale for handling Fair comparison, linking it to the code.
Prerequisites
Prepare the experiment results for Maximum and Capacity calculation from Unit 12, “Capacity Limits and Failure”.
Key concepts and explanations
Call count
Calling an export for every element repeatedly crosses the boundary. A batch calls once and loops internally.
Fair comparison
Use identical data and the same sum contract. Record copy time separately as well.
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-13.mjs in a separate practice project, run the existing at loop and sum(0,n) on the same array. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: 100 and 100003 integers. Baseline: at for each element. Run under the baseline conditions, then record observations and errors in notes/day-13.md.
- Variable: call method; changed value: one sum call. Run again through the same input path. Deliverable to save: call counts·sums·measured times. Hypothesis to check: The result is the same, and the number of boundary calls decreases. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| call method | at for each element | one sum call | The result is the same, and the number of boundary calls decreases. |
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: call counts·sums·measured times. 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: Call count and Fair comparison. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Call count affect in this exercise? Input cases: 100 and 100003 integers.
- Variable: call method. Hypothesis to check: The result is the same, and the number of boundary calls decreases. Did the actual results agree with the hypothesis? Explain the evidence in terms of Fair comparison.
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: Capacity Limits and Failure · Next: Arrays and Boundary Costs