TypeScript Strict Mode: lima kegagalan runtime yang dicegah

TypeScript Strict Mode bukan sekadar gaya. Ia memindahkan kegagalan produksi ke editor: nilai null yang hilang, any yang menyebar, akses indeks berbahaya, kontrak fungsi lemah, dan JSON tanpa validasi. Data eksternal sebaiknya masuk sebagai unknown, divalidasi di batas, lalu diubah menjadi model internal yang stabil.

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1. null dan undefined

TypeScript Strict Mode bukan sekadar gaya. Ia memindahkan kegagalan produksi ke editor: nilai null yang hilang, any yang menyebar, akses indeks berbahaya, kontrak fungsi lemah, dan JSON tanpa validasi. Data eksternal sebaiknya masuk sebagai unknown, divalidasi di batas, lalu diubah menjadi model internal yang stabil. The practical rule is to decide behavior before runtime: empty state, fallback value, controlled error, or validated model. This keeps reviews focused and prevents hidden assumptions from reaching users.

2. any menyebar

3. indeks tidak aman

4. kontrak lemah

5. JSON tanpa validasi

Rollout checklist

• Enable strict in a branch and group errors by risk.
• Start with null handling and external data boundaries.
• Replace implicit any with unknown plus validation.
• Add explicit return types to public functions.
• Keep temporary casts visible until they are removed.

FAQ

Does Strict Mode slow development?

During migration it can, but it reduces production rework by exposing shape and contract errors earlier.

Is optional chaining enough?

No. It prevents one crash but does not decide the user experience when data is missing.

Do schema libraries matter?

Small boundaries can use handwritten guards. Larger products benefit from shared schemas.