TypeScript Best Practices

Goal

Make code safer and easier to change. Use TypeScript to model real constraints without adding noise.

Rules

• Prefer unknown over any.
• Let inference work for local values.
• Add explicit types at boundaries: exports, API input/output, public functions.
• Enable strict compiler options when project allows.
• Use discriminated unions for state variants.
• Narrow unknown data before use.
• Prefer interface for object shapes.
• Prefer type for unions and utility types.
• Avoid type assertions unless crossing a known boundary.
• Keep runtime validation near external input.