typescript-strict

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TypeScript Strict Mode

TypeScript严格模式

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

针对现代TypeScript的严格类型检查配置，可实现最大程度的类型安全与最优开发体验。本指南聚焦2025年TypeScript 5.x版本的最佳实践。

When to Use This Skill

适用场景

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)

以下场景可使用本指南	以下场景请选择其他方案
搭建新的TypeScript项目	调试运行时错误（请使用调试器）
迁移至更严格的类型安全规范	配置构建工具（请参考打包工具文档）
选择moduleResolution策略	编写应用业务逻辑
启用noUncheckedIndexedAccess配置	优化打包体积（请使用打包工具相关技能）

Core Expertise

核心特性

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

什么是严格模式？

类型安全：在编译阶段捕获更多Bug
更优的IDE体验：更完善的自动补全与重构支持
可维护性：显式类型让代码实现自文档化
现代默认配置：与当前TypeScript最佳实践对齐

核心能力

严格空值检查
严格函数类型
禁用隐式any类型
禁用未检查的索引访问
合理的模块解析规则
现代import/export语法强制校验

Recommended tsconfig.json (2025)

2025年推荐tsconfig.json配置

Minimal Production Setup

最简生产环境配置

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"]
}

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

严格配置项详解

strict: true

(Umbrella Flag)

strict: true

（总开关）

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.

启用所有严格类型检查选项：

json

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

新项目请始终启用
strict: true
。

Additional Strict Flags (Recommended for 2025)

2025年推荐的额外严格配置项

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

配置项	作用
`noUncheckedIndexedAccess`	索引签名返回值类型为 `T \| undefined` 而非 `T`
`noImplicitOverride`	重写父类方法时必须显式使用 `override` 关键字
`noPropertyAccessFromIndexSignature`	访问索引签名属性时必须使用方括号写法
`noFallthroughCasesInSwitch`	禁止switch语句中出现case穿透
`exactOptionalPropertyTypes`	可选属性不可被显式赋值为 `undefined`

noUncheckedIndexedAccess

(Essential)

noUncheckedIndexedAccess

（核心必备）

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.

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
}

请始终启用该配置项以避免运行时错误。

Module Resolution

模块解析

Choosing a Strategy

策略选择

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

策略	适用场景	需要文件后缀
`Bundler`	Vite、Webpack、Bun项目	不需要
`NodeNext`	Node.js库与服务端项目	是（ `.js` ）

moduleResolution: "Bundler"

(Vite/Bun)

moduleResolution: "Bundler"

（适用于Vite/Bun）

json

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

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

json

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

导入时不需要加文件后缀
导入JSON无需添加断言
支持package.json
```
exports
```
字段

moduleResolution: "NodeNext"

(Node.js)

moduleResolution: "NodeNext"

（适用于Node.js）

json

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

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

json

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

遵循package.json
```
type: "module"
```
配置
导入需要显式添加
```
.js
```
后缀（即便原文件是
```
.ts
```
格式）
支持条件导出

verbatimModuleSyntax (Recommended for 2025)

verbatimModuleSyntax（2025年推荐启用）

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

禁止TypeScript重写import/export语句。

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';

该配置项已替代已废弃的

importsNotUsedAsValues

与

preserveValueImports

配置。

Agentic Optimizations

快捷命令

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`

场景	命令
检查类型错误	`bunx tsc --noEmit`
检查单个文件	`bunx tsc --noEmit src/utils.ts`
查看生效配置	`bunx tsc --showConfig`
检查模块解析配置	`bunx tsc --showConfig \| grep moduleResolution`

Quick Reference

快速参考

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

配置项	取值	分类
`strict`	`true`	类型检查
`noUncheckedIndexedAccess`	`true`	类型检查
`noImplicitOverride`	`true`	类型检查
`noPropertyAccessFromIndexSignature`	`true`	类型检查
`noFallthroughCasesInSwitch`	`true`	类型检查
`module`	`ESNext` / `NodeNext`	模块配置
`moduleResolution`	`Bundler` / `NodeNext`	模块配置
`verbatimModuleSyntax`	`true`	模块配置
`target`	`ES2022`	编译输出
`isolatedModules`	`true`	兼容性配置
`skipLibCheck`	`true`	兼容性配置

References

参考资料

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 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

Original

Translation

TypeScript Strict Mode

TypeScript严格模式

When to Use This Skill

适用场景

Core Expertise

核心特性

Recommended tsconfig.json (2025)

2025年推荐tsconfig.json配置

Minimal Production Setup

最简生产环境配置

Strict Flags Explained

严格配置项详解

`strict: true`
(Umbrella Flag)

`strict: true`
（总开关）

Additional Strict Flags (Recommended for 2025)

2025年推荐的额外严格配置项

`noUncheckedIndexedAccess`
(Essential)

`noUncheckedIndexedAccess`
（核心必备）

Module Resolution

模块解析

Choosing a Strategy

策略选择

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

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

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

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

verbatimModuleSyntax (Recommended for 2025)

verbatimModuleSyntax（2025年推荐启用）

Agentic Optimizations

快捷命令

Quick Reference

快速参考

Recommended Flags

推荐配置项

References

参考资料

typescript-strict

Original

Translation

TypeScript Strict Mode

TypeScript严格模式

When to Use This Skill

适用场景

Core Expertise

核心特性

Recommended tsconfig.json (2025)

2025年推荐tsconfig.json配置

Minimal Production Setup

最简生产环境配置

Strict Flags Explained

严格配置项详解

strict: true (Umbrella Flag)

strict: true（总开关）

Additional Strict Flags (Recommended for 2025)

2025年推荐的额外严格配置项

noUncheckedIndexedAccess (Essential)

noUncheckedIndexedAccess（核心必备）

Module Resolution

模块解析

Choosing a Strategy

策略选择

moduleResolution: "Bundler" (Vite/Bun)

moduleResolution: "Bundler"（适用于Vite/Bun）

moduleResolution: "NodeNext" (Node.js)

moduleResolution: "NodeNext"（适用于Node.js）

verbatimModuleSyntax (Recommended for 2025)

verbatimModuleSyntax（2025年推荐启用）

Agentic Optimizations

快捷命令

Quick Reference

快速参考

Recommended Flags

推荐配置项

References

参考资料

`strict: true`
(Umbrella Flag)

`strict: true`
（总开关）

`noUncheckedIndexedAccess`
(Essential)

`noUncheckedIndexedAccess`
（核心必备）

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

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

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

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