docs: clarify that observable() mutates input by reference#652
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observable() stores plain object/array inputs by reference and mutates them in place as fields are updated. This surprises people coming from Zustand/Redux/MobX and produces silent footguns when a shared `initialState` constant is reused as a "reset target" — the constant becomes structurally equal to current state, so set() is a no-op. Add JSDoc to observable() with a minimal repro and the recommended factory-function pattern. Refs LegendApp#647 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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Closing in favor of legendapp/legend-docs#59, which adds the same guidance to the docs site (the canonical source). Happy to revive this as a JSDoc on top of the docs change if you'd find that useful. |
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Adds a JSDoc note on
observable()explaining that plain object/array inputs are stored by reference and mutated in place as fields are updated.This is intentional (avoids cloning on every update) but surprises people coming from Zustand/Redux/MobX, and produces silent footguns when a shared
initialStateconstant is reused as a "reset target" — the constant becomes structurally equal to current state, soset()ends up a no-op via the deep-equals check.The JSDoc includes a minimal repro and the recommended factory pattern.
Refs #647 — when I dug into that issue, the original sync-bug framing turned out to be wrong; the real cause is this mutation behavior. I then audited my own codebase and found 8 stores with silently-broken reset functions from the same pattern.
No code/behavior changes — JSDoc only.
Disclosure: written together with Claude (Anthropic). Verified locally.