is-kit Reached 50 Stars ⭐ Here’s How We Use It in Production

Description and use

In a large TypeScript app, replaced repetitive type guard checks with composable functions from is-kit, cutting code by 249 lines and improving readability.

Problem

Repeated, boilerplate type guard checks for unknown values caused code duplication, assertion casts, and maintenance pain.

Outcome

Consolidated guard logic, eliminated repetitive casts, centralized primitive semantics, and reduced code size by 249 lines, improving maintainability and type safety.

Workflow

• 1. Install is-kit via pnpm
• 2. Define base guard with define and equalsKey
• 3. Create composable status guard isHttpErrorWithStatus
• 4. Export specific guards (e.g., isUnauthorizedError)
• 5. Wrap library guards in app‑owned helpers for consistent naming
• 6. Replace legacy checks with these helpers across the codebase
• 7. Update team guidelines to prefer combinators like or and and

Evidence

After using it in the application, the advantages became clearer.

Source

The first adoption refactor was not just 👇 pnpm add is-kit

Source