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Rule priority, scope & exceptions
Use this to align rules with the senior-level structure (P0/P1/P2, scope, exceptions/tradeoffs).
fullstack ruleP1universalStack: TypeScript / JavaScript
typescriptnarrowingcorrectnessoperators
Use the right existence check: `in` for optional keys, null check for nullable values
The `in` operator tests key presence, not value. For a property that's always present but may be null, compare the value; reserve `in` for genuinely optional keys.
PR: hegnar-bellsheep-web · org-mining-hist-2026-06Created: Jun 18, 2026
Bad example
Old codets
| 1 | if ('fullname' in entry) { ... } // true even when entry.fullname === null |
Explanation (EN)
Objašnjenje (HR)
Good example
New codets
| 1 | if (entry.fullname !== null) { ... } |
Explanation (EN)
Objašnjenje (HR)