Use exact string values for safer APIs.
Section: Primitive Types and Annotations
Restrict values with literal unions
typescript
typescript
type Theme = "light" | "dark" | "system";
const theme: Theme = "dark";Explanation
Literal unions are ideal for config values, modes, and command flags.
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Same sheet · prioritizing Primitive Types and Annotations
Freeze literals with `as const`
Preserve readonly literal values for objects and arrays.
Annotate basic variables
Explicitly type strings, numbers, and booleans.
Annotate object shapes
Describe the expected properties of an object.