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WebAssembly · 11 Memory Grow and View Lifetime
Series contents · Technology map
Stage: Memory and Array Boundaries · External example · preview instructions · Storage ID: webassembly-step-11
Goals and learning outcomes
- Learning outcome: explain the role of Grow. Input cases: one non-shared memory.
- Deliverable: capacity before·after growth and old/new view lengths. Explain the rationale for handling Recreation, linking it to the code.
Prerequisites
Prepare the experiment results for Set and Bounds from Unit 10, “Array Copies and Bounds”.
Key concepts and explanations
Grow
memory.grow increases capacity in pages. Views of the existing non-shared buffer may become invalid.
Recreation
Recreate views from memory.buffer after growth. Code that caches old views must also update them.
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-11.mjs in a separate practice project, keep the existing view and compare its byteLength with a new view after grow(1). Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: one non-shared memory. Baseline: none. Run under the baseline conditions, then record observations and errors in notes/day-11.md.
- Variable: grow; changed value: 1 page. Run again through the same input path. Deliverable to save: capacity before·after growth and old/new view lengths. Hypothesis to check: The existing view becomes invalid, and the new view can read the data. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| grow | none | 1 page | The existing view becomes invalid, and the new view can read the data. |
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: capacity before·after growth and old/new view lengths. 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: Grow and Recreation. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Grow affect in this exercise? Input cases: one non-shared memory.
- Variable: grow. Hypothesis to check: The existing view becomes invalid, and the new view can read the data. Did the actual results agree with the hypothesis? Explain the evidence in terms of Recreation.
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: Array Copies and Bounds · Next: Capacity Limits and Failure