ts-language-patterns

Replace enum with a const object using as const, then derive the union type with keyof typeof. For example, `const Status = { Active: "active" } as const` with `type Status = (typeof Status)[keyof typeof Status]` is erasable by Node's type stripper and tree-shakeable.

Prefix a type parameter with const, like `function first<const T extends readonly unknown[]>(arr: T)`, so arguments infer the narrowest literal type without callers writing as const. The constraint still applies, and it only affects call-site inference.

Yes, TypeScript implements the TC39 Stage 3 standard decorators receiving (value, context) with typed contexts like ClassMethodDecoratorContext. Do not enable experimentalDecorators or emitDecoratorMetadata, and note decorators require a compiler or bundler since Node's type stripper does not transform them.

Under verbatimModuleSyntax, a type imported without the type keyword is treated as a value import and crashes Node at runtime. Use `import type { User }` or inline markers like `import { createUser, type CreateUserInput }` for all type-only imports.

Use using when a value owns a resource with a Symbol.dispose method, such as file handles or connections. It guarantees cleanup in reverse order even on throw, and await using with Symbol.asyncDispose handles asynchronous teardown inside async functions.

A satisfies clause validates a value against a type while keeping its narrow inferred type, whereas a plain annotation widens the value to the annotated type. Use satisfies when you still need member-level specificity, such as preserving tuple or literal types.