Typescript Professional Usage

typescript-professional-usage

Registry Trigger

Use when

• TypeScript code changes trust-boundary validation, structural assignability, unsafe escapes, async cancellation, numeric meaning, emitted modules, or public declarations.
• Browser, Node, SDK, generated-client, storage, message, or package-export behavior can differ from what the type checker accepts.

Do not use when

• The open question is generic frontend state, API policy, package/build configuration, performance, testing, or language style without a TypeScript-specific semantic risk.
• No TypeScript source, declaration, generated surface, compiler boundary, or emitted runtime behavior changes.

Skill Role

Protect TypeScript runtime narrowing, structural-type limits, unsafe escapes, promise and cancellation behavior, JavaScript numeric semantics, and emitted-module compatibility. Exclude product-state, API, package, and bundler decisions.

High-Value Rules

• Treat external, persisted, versioned, generated, and cross-realm data as untrusted until an owned runtime parser establishes the accepted shape and maps invalid input to a caller-visible outcome.
• Structural assignability can admit extra capabilities, lose nominal identity, or collapse absent and present-undefined; use discriminants, exact parsers, brands, or satisfies when a concrete invariant requires them, not as universal decoration.
• Scope any, assertions, non-null operators, and suppressions to inspected evidence; an escape at a trust, storage, generated, or public boundary has an owner and cleanup trigger.
• Observe every owned promise and background task, propagate AbortSignal or equivalent cancellation where the boundary supports it, and settle cleanup and state transitions for rejection, timeout, and stale completion.
• Classify safe integers, fractions, NaN, infinities, decimal money, bigint, serialized numbers, and units wherever conversion or comparison changes behavior.
• Review type-only versus runtime imports, side effects, ESM/CJS and conditional exports, module resolution, declaration emission, and generated entrypoints against each supported runtime and build target.
• Verify public-type and generated-contract changes with named consumer compilation plus runtime version-skew cases; typecheck success remains scoped to the selected config, files, and module graph.

Anti-Patterns

• A type annotation, assertion, schema type, or successful compilation is treated as runtime validation.
• Structural compatibility lets a database/domain object or authority-bearing value cross a DTO, SDK, storage, or message boundary unchanged.
• A floating promise, broad catch, default value, or stale completion hides rejection, cancellation, or user-visible state.
• Type tests pass while emitted imports, package exports, side effects, declarations, or numeric serialization fail at runtime.

Stop Conditions

• Stop fail-closed when decisive runtime, consumer, module-emission, or validation evidence is unknown or unavailable.
• Do not select behavior from typecheck-only or assumed evidence.
• Route API/SDK, product-state, money/timezone, security, package, build, runtime-performance, and testing decisions to their named owners.

Output Contract

• TypeScript semantic decision with runtime boundary structural-type limit bounded escape async cancellation numeric behavior module emission public/generated compatibility proof limits and specialist routes

Targeted References