testdino-hq Google TypeScript Style Guide
Official Google TypeScript coding standards for consistent, maintainable code.
Golden Rules
- Use TypeScript strictly — enable
strictmode intsconfig.json - Prefer interfaces over type aliases for object shapes
- Never use
any— useunknownwhen type is truly unknown - Use
constby default,letwhen reassignment needed, nevervar - Avoid non-null assertions (
!) — handle nullability explicitly - Use explicit return types on public functions and methods
- Prefer
readonlyfor properties that should not change
Quick Reference
Naming Conventions
| Element | Convention | Example |
|---|---|---|
| Classes/Interfaces | UpperCamelCase | UserService, User |
| Functions/Methods | lowerCamelCase | getUserById |
| Variables | lowerCamelCase | userCount |
| Constants | UPPER_SNAKE_CASE | MAX_SIZE |
| Enums | UpperCamelCase | Direction |
| Enum members | UPPER_SNAKE_CASE or UpperCamelCase | Direction.UP or Status.Active |
| Files | lower-kebab-case | user-service.ts |
| Test files | lower-kebab-case_test | user-service_test.ts |
Type System
// ✓ CORRECT - interfaces for object shapes
interface User {
id: number;
name: string;
}
// ✓ CORRECT - type aliases for unions
type StringOrNumber = string | number;
// ✗ INCORRECT - avoid any
const data: any = fetchData();
// ✓ CORRECT - use unknown and narrow
const data: unknown = fetchData();
if (typeof data === 'string') {
console.log(data.toUpperCase());
}
Null Handling
// ✓ CORRECT - explicit nullability
function getUser(id: number): User | undefined {
return users.find(u => u.id === id);
}
const user = getUser(1);
if (user !== undefined) {
console.log(user.name);
}
// ✗ INCORRECT - non-null assertion
const user = getUser(1)!;
Functions
// ✓ CORRECT - explicit return types for public API
function add(a: number, b: number): number {
return a + b;
}
// ✓ CORRECT - arrow functions for callbacks
const double = (x: number): number => x * 2;
// ✓ CORRECT - optional parameters with defaults
function greet(name: string, greeting = 'Hello'): string {
return `${greeting}, ${name}!`;
}
Imports
// ✓ CORRECT - named exports
export function myFunction() { /* ... */ }
export interface MyInterface { id: number; }
// ✓ CORRECT - type-only imports
import type { MyInterface } from './types';
import { myFunction } from './my-module';
// ✗ INCORRECT - wildcard imports
import * as everything from './module';
Common Mistakes
| Mistake | Correct Approach |
|---|---|
Using any type |
Use unknown + type narrowing |
Non-null assertion ! |
Check for null explicitly |
var declarations |
Use const / let |
| Missing return types | Add explicit return types |
| Wildcard imports | Use named imports |
| Mutable class properties | Use readonly when appropriate |
| Type aliases for objects | Use interfaces instead |
tsconfig.json Recommended Settings
{
"compilerOptions": {
"strict": true,
"noImplicitAny": true,
"strictNullChecks": true,
"noImplicitReturns": true,
"noFallthroughCasesInSwitch": true,
"esModuleInterop": true,
"skipLibCheck": true
}
}
When to Use This Guide
- Writing new TypeScript code
- Refactoring existing TypeScript
- Code reviews
- Setting up linting rules
- Onboarding new team members
Install
npx skills add testdino-hq/google-styleguides-skills/typescript
Full Guide
See typescript.md for complete details, examples, and edge cases.