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Typescript Strict Mode

Development
typescript-strict-mode

Typescript Strict Mode is an Agent Skill for development published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.

Use when setting up a new TypeScript project, auditing an existing tsconfig.json, or reviewing code where null-reference errors or implicit any types are present.

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QUICK START

How to use this skill

Bring this guide into your coding agent with a prompt tailored to the tool you use.

  1. Open your project in Codex.
  2. Copy and paste the prompt below.
  3. Review files and risks before approving any action.
Prompt to paste
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/typescript-strict-mode/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/typescript-strict-mode, but wait for my approval before writing files or running scripts.

Copying this prompt does not install or run the skill. Review third-party files before use.

Enable TypeScript strict mode in tsconfig.json

Without strict mode, TypeScript allows implicit any types, ignores possible null/undefined values, and silently accepts unsound function assignments — meaning the type system gives a false sense of safety. Enabling strict mode makes TypeScript catch the bugs it was designed to prevent, turning type errors into compile-time failures rather than runtime surprises in production.

Quick Reference

  • "strict": true enables strictNullChecks, noImplicitAny, and six other checks
  • Enable strict from project start — retrofitting a large codebase is painful
  • On existing projects: enable strictNullChecks first, then other flags incrementally
  • Strict mode eliminates entire classes of null reference and implicit-any bugs

Check

Inspect the tsconfig.json in this project and report whether "strict": true (or individual strict flags) is enabled. List any missing strict flags.

Fix

Add "strict": true to the compilerOptions in tsconfig.json. If the project has existing type errors, explain how to enable strictNullChecks first as a stepping stone.

Explain

Explain what TypeScript strict mode enables, which individual flags it activates, and why each flag matters for catching real bugs.

Code Review

Check whether the codebase relies on implicit any, unchecked null access, or loose function type assignments that strict mode would reject. Flag the specific patterns and show what stricter types would look like.

For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/en/rules/javascript/typescript-strict-mode