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WebAssembly · 09 Views and Endianness
Series contents · Technology map
Stage: Memory and Array Boundaries · External example · preview instructions · Storage ID: webassembly-step-09
Goals and learning outcomes
- Learning outcome: explain the role of Shared storage. Input cases: one 32-bit integer.
- Deliverable: four bytes and the reconstructed number. Explain the rationale for handling Byte order, linking it to the code.
Prerequisites
Prepare the experiment results for Pages and Pointers from Unit 8, “Pages and Byte Offset”.
Key concepts and explanations
Shared storage
Different TypedArrays interpret the same bytes differently. Creating a view does not copy the data.
Byte order
Numeric values in Wasm memory use little-endian layout. Explicitly setting the order in DataView makes interpretation clear.
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-9.mjs in a separate practice project, write 0x12345678 with DataView in little-endian order and read it with Uint8Array. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: one 32-bit integer. Baseline: little-endian. Run under the baseline conditions, then record observations and errors in notes/day-9.md.
- Variable: interpretation order; changed value: big-endian. Run again through the same input path. Deliverable to save: four bytes and the reconstructed number. Hypothesis to check: The number read from the same bytes changes. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| interpretation order | little-endian | big-endian | The number read from the same bytes changes. |
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: four bytes and the reconstructed number. 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: Shared storage and Byte order. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Shared storage affect in this exercise? Input cases: one 32-bit integer.
- Variable: interpretation order. Hypothesis to check: The number read from the same bytes changes. Did the actual results agree with the hypothesis? Explain the evidence in terms of Byte order.
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: Pages and Byte Offset · Next: Array Copies and Bounds