typescript-strict

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Translated

TypeScript strict mode configuration for 2025. Recommended tsconfig.json settings, strict flags explained, moduleResolution strategies (Bundler vs NodeNext), verbatimModuleSyntax, noUncheckedIndexedAccess. Use when setting up TypeScript projects or migrating to stricter type safety.

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Sourcelaurigates/claude-plugins

Added on2026-02-28

NPX Install

npx skill4agent add laurigates/claude-plugins typescript-strict

SKILL.md Content

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TypeScript Strict Mode

Modern TypeScript configuration with strict type checking for maximum safety and developer experience. This guide focuses on TypeScript 5.x best practices for 2025.

When to Use This Skill

Use this skill when...	Use another approach when...
Setting up a new TypeScript project	Debugging runtime errors (use debugger)
Migrating to stricter type safety	Configuring build tools (use bundler docs)
Choosing moduleResolution strategy	Writing application logic
Enabling noUncheckedIndexedAccess	Optimizing bundle size (use bundler skills)

Core Expertise

What is Strict Mode?

Type safety: Catch more bugs at compile time
Better IDE experience: Improved autocomplete and refactoring
Maintainability: Self-documenting code with explicit types
Modern defaults: Align with current TypeScript best practices

Key Capabilities

Strict null checking
Strict function types
No implicit any
No unchecked indexed access
Proper module resolution
Modern import/export syntax enforcement

Recommended tsconfig.json (2025)

Minimal Production Setup

json

{
  "compilerOptions": {
    // Type Checking
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,
    "noPropertyAccessFromIndexSignature": true,
    "noFallthroughCasesInSwitch": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,

    // Modules
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "resolveJsonModule": true,
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": false,
    "verbatimModuleSyntax": true,

    // Emit
    "target": "ES2022",
    "lib": ["ES2023", "DOM", "DOM.Iterable"],
    "outDir": "dist",
    "declaration": true,
    "declarationMap": true,
    "sourceMap": true,
    "removeComments": false,
    "noEmit": false,

    // Interop
    "isolatedModules": true,
    "allowJs": false,
    "checkJs": false,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules", "dist", "build"]
}

Strict Flags Explained

strict: true

(Umbrella Flag)

Enables all strict type-checking options:

json

{
  "strict": true
  // Equivalent to:
  // "noImplicitAny": true,
  // "strictNullChecks": true,
  // "strictFunctionTypes": true,
  // "strictBindCallApply": true,
  // "strictPropertyInitialization": true,
  // "noImplicitThis": true,
  // "alwaysStrict": true
}

Always enable
strict: true
for new projects.

Additional Strict Flags (Recommended for 2025)

Flag	Purpose
`noUncheckedIndexedAccess`	Index signatures return `T \| undefined` instead of `T`
`noImplicitOverride`	Require `override` keyword for overridden methods
`noPropertyAccessFromIndexSignature`	Force bracket notation for index signatures
`noFallthroughCasesInSwitch`	Prevent fallthrough in switch statements
`exactOptionalPropertyTypes`	Optional properties cannot be set to `undefined` explicitly

noUncheckedIndexedAccess

(Essential)

typescript

// With noUncheckedIndexedAccess
const users: Record<string, User> = {};
const user = users['john'];
// Type: User | undefined (correct - must check before use)

if (user) {
  console.log(user.name); // Type narrowed to User
}

Always enable this flag to prevent runtime errors.

Module Resolution

Choosing a Strategy

Strategy	Use For	Extensions Required
`Bundler`	Vite, Webpack, Bun projects	No
`NodeNext`	Node.js libraries and servers	Yes ( `.js` )

moduleResolution: "Bundler"

(Vite/Bun)

json

{
  "compilerOptions": {
    "module": "ESNext",
    "moduleResolution": "Bundler"
  }
}

No file extensions required in imports
JSON imports without assertions
Package.json
```
exports
```
field support

moduleResolution: "NodeNext"

(Node.js)

json

{
  "compilerOptions": {
    "module": "NodeNext",
    "moduleResolution": "NodeNext"
  }
}

Respects package.json
```
type: "module"
```
Requires explicit
```
.js
```
extensions (even for
```
.ts
```
files)
Supports conditional exports

verbatimModuleSyntax (Recommended for 2025)

Prevents TypeScript from rewriting imports/exports.

json

{
  "compilerOptions": {
    "verbatimModuleSyntax": true
  }
}

typescript

// Error: 'User' is a type and must be imported with 'import type'
import { User } from './types';

// Correct
import type { User } from './types';

// Correct (mixed import)
import { fetchUser, type User } from './api';

Replaces deprecated

importsNotUsedAsValues

and

preserveValueImports

.

Agentic Optimizations

Context	Command
Check errors	`bunx tsc --noEmit`
Check single file	`bunx tsc --noEmit src/utils.ts`
Show config	`bunx tsc --showConfig`
Check module resolution	`bunx tsc --showConfig \| grep moduleResolution`

Quick Reference

Recommended Flags

Flag	Value	Category
`strict`	`true`	Type Checking
`noUncheckedIndexedAccess`	`true`	Type Checking
`noImplicitOverride`	`true`	Type Checking
`noPropertyAccessFromIndexSignature`	`true`	Type Checking
`noFallthroughCasesInSwitch`	`true`	Type Checking
`module`	`ESNext` / `NodeNext`	Modules
`moduleResolution`	`Bundler` / `NodeNext`	Modules
`verbatimModuleSyntax`	`true`	Modules
`target`	`ES2022`	Emit
`isolatedModules`	`true`	Interop
`skipLibCheck`	`true`	Interop

For detailed examples, advanced patterns, and best practices, see REFERENCE.md.

References

TypeScript Handbook: https://www.typescriptlang.org/docs/handbook/intro.html
TSConfig Reference: https://www.typescriptlang.org/tsconfig
Strict Mode Guide: https://www.typescriptlang.org/tsconfig#strict
Module Resolution: https://www.typescriptlang.org/docs/handbook/module-resolution.html
Best Practices: https://www.typescriptlang.org/docs/handbook/declaration-files/do-s-and-don-ts.html

typescript-strict

NPX Install

Tags

SKILL.md Content

TypeScript Strict Mode

When to Use This Skill

Core Expertise

Recommended tsconfig.json (2025)

Minimal Production Setup

Strict Flags Explained

`strict: true`
(Umbrella Flag)

Additional Strict Flags (Recommended for 2025)

`noUncheckedIndexedAccess`
(Essential)

Module Resolution

Choosing a Strategy

`moduleResolution: "Bundler"`
(Vite/Bun)

`moduleResolution: "NodeNext"`
(Node.js)

verbatimModuleSyntax (Recommended for 2025)

Agentic Optimizations

Quick Reference

Recommended Flags

References