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WebAssembly · 02 WAT and Binary
Series contents · Technology map
Stage: Modules and Numeric Contracts · External example · preview instructions · Storage ID: webassembly-step-02
Goals and learning outcomes
- Learning outcome: explain the role of Text format. Input cases: the existing sum function and a modified constant.
- Deliverable: build logs and export call results. Explain the rationale for handling Build, linking it to the code.
Prerequisites
Prepare the experiment results for Module boundary and Preview scope from Unit 1, “Modules and Linear Memory”.
Key concepts and explanations
Text format
WAT is a readable representation of module structure. Browsers do not directly execute a WAT string as a Wasm binary.
Build
wat2wasm converts text into binary. Check build results separately from execution results.
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-2.mjs in a separate practice project, copy kernel.wat into a separate folder and run the official tool: wat2wasm kernel.wat -o kernel.wasm. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: the existing sum function and a modified constant. Baseline: valid WAT. Run under the baseline conditions, then record observations and errors in notes/day-2.md.
- Variable: source; changed value: WAT with a syntax error. Run again through the same input path. Deliverable to save: build logs and export call results. Hypothesis to check: Syntax errors are exposed during the build. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| source | valid WAT | WAT with a syntax error | Syntax errors are exposed during the build. |
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: build logs and export call 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: Text format and Build. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Text format affect in this exercise? Input cases: the existing sum function and a modified constant.
- Variable: source. Hypothesis to check: Syntax errors are exposed during the build. Did the actual results agree with the hypothesis? Explain the evidence in terms of Build.
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: Modules and Linear Memory · Next: Compile and Instance