Large-scale project management

Core Challenges of Large-Scale Project Management

Large TypeScript projects typically involve collaboration among multiple teams, complex dependency relationships, and long-term maintenance requirements. When code volume exceeds 100,000 lines, traditional development models encounter issues such as slower build speeds, slower type checking, and high module coupling. For example, after an e-commerce platform's frontend project upgraded to TypeScript 4.5, type-checking time increased from 23 seconds to 47 seconds, directly impacting developers' iteration efficiency.

Modular Architecture Design

Adopting Domain-Driven Design (DDD) to define module boundaries is an effective way to manage complexity. Large applications can be split into:

src/  
├── core/               // Core utility library  
├── payment/            // Payment domain  
│   ├── entities/       // Domain entities  
│   ├── services/       // Domain services  
│   └── adapters/       // External service adapters  
├── order/              // Order domain  
└── shared/             // Shared resources  

Each module should expose clear interfaces via index.ts:

// payment/index.ts  
export { PaymentService } from './services/payment-service';  
export type { PaymentMethod } from './entities/payment-method';  
export { StripeAdapter } from './adapters/stripe-adapter';  

Type System Optimization Strategies

Use type guards to reduce type assertions:

function isApiError(error: unknown): error is ApiError {  
  return typeof error === 'object'   
    && error !== null   
    && 'code' in error   
    && typeof (error as any).code === 'number';  
}  

try {  
  await fetchData();  
} catch (err) {  
  if (isApiError(err)) {  
    console.error(`API Error: ${err.code}`);  
  }  
}  

Application of generic constraints in complex scenarios:

interface Repository<T extends { id: string }> {  
  get(id: string): Promise<T>;  
  save(entity: T): Promise<void>;  
}  

class UserRepository implements Repository<User> {  
  // Must implement methods with specific signatures  
}  

Build Performance Tuning

Split monorepo using Project References:

// tsconfig.base.json  
{  
  "compilerOptions": {  
    "composite": true,  
    "incremental": true  
  }  
}  

// packages/core/tsconfig.json  
{  
  "extends": "../../tsconfig.base.json",  
  "references": [{ "path": "../shared" }]  
}  

Measured data shows that after adopting this configuration in a financial system:

• Full build time decreased from 4.2 minutes to 1.8 minutes
• Average incremental build time dropped from 32 seconds to 9 seconds
• Peak memory usage reduced by 40%

Code Quality Assurance System

Combining ESLint with type-checking hybrid rules:

// .eslintrc.js  
module.exports = {  
  plugins: ['@typescript-eslint'],  
  rules: {  
    '@typescript-eslint/no-unsafe-assignment': 'error',  
    '@typescript-eslint/no-floating-promises': 'error',  
    '@typescript-eslint/consistent-type-imports': 'warn'  
  }  
};  

Example of custom type-safe rules:

type StrictNullCheck<T> = T extends null | undefined ? never : T;  

function requireNonNull<T>(value: T): StrictNullCheck<T> {  
  if (value == null) throw new Error('Null check failed');  
  return value as StrictNullCheck<T>;  
}  

Team Collaboration Standards

Version control strategy combined with Git workflow:

# Feature branch naming convention  
git checkout -b feat/payment/add-wechat-pay  

# Commit message format  
<type>(<scope>): <subject>  
// Example  
fix(core): resolve memory leak in event emitter  

Code reviews should focus on:

1. Changes to public API type signatures
2. Cross-module dependencies
3. Exception handling edge cases
4. Type annotations for performance-sensitive operations

Continuous Integration Practices

Example of a phased CI configuration:

# .github/workflows/ci.yml  
jobs:  
  type-check:  
    steps:  
      - run: tsc --build --force --verbose  
  unit-test:  
    needs: type-check  
    steps:  
      - run: jest --config jest.config.ts  
  integration-test:  
    needs: unit-test  
    steps:   
      - run: cypress run --component  

Key metric monitoring thresholds:

• Type-checking timeout: > 90 seconds triggers an alert
• Test coverage: < 80% blocks merging
• Build artifact size: > 10% growth requires review

Advanced Dependency Management Techniques

Using Yarn Workspaces to manage monorepo dependencies:

// package.json  
{  
  "private": true,  
  "workspaces": ["packages/*"],  
  "resolutions": {  
    "@types/react": "17.0.3"  
  }  
}  

Third-party type definition maintenance strategy:

1. Prefer @types packages from DefinitelyTyped
2. Write type extension declarations for complex SDKs:

// types/custom-sdk.d.ts  
declare module 'vendor-sdk' {  
  interface SDKConfig {  
    timeout: number;  
    retry?: boolean;  
  }  

  export function init(config: SDKConfig): Promise<void>;  
}  

Documentation Automation Solutions

Generating type documentation with TSDoc:

/**  
 * Handle payment result callback  
 * @remarks  
 * Supports async notification verification and synchronous result return  
 *  
 * @param payload - Callback data payload  
 * @returns Processing result and redirect path  
 *  
 * @example  
 * ```ts  
 * await handleCallback({  
 *   orderId: '123',  
 *   status: 'paid'  
 * });  
 * ```  
 */  
export async function handleCallback(payload: CallbackPayload) {  
  // Implementation logic  
}  

Generating architecture diagrams with Compodoc:

npx compodoc -p tsconfig.json --format json --output docs  

Performance Analysis and Optimization

Using TypeScript compiler API for custom analysis:

import ts from 'typescript';  

function checkTypeDepth(node: ts.Node, depth = 0): number {  
  if (ts.isTypeNode(node)) {  
    return 1 + Math.max(  
      ...node.getChildren().map(child =>   
        checkTypeDepth(child, depth + 1)  
      )  
    );  
  }  
  return depth;  
}  

Typical optimization cases:

• Refactor nested types deeper than 5 levels into interfaces
• Identify the top 10 type definitions with the longest compilation times
• Automatically detect composite types with over 200 union types

Error Handling Patterns

Type-safe error classification scheme:

class Result<T, E extends Error> {  
  private constructor(  
    private readonly value?: T,  
    private readonly error?: E  
  ) {}  

  static ok<T>(value: T): Result<T, never> {  
    return new Result(value);  
  }  

  static fail<E extends Error>(error: E): Result<never, E> {  
    return new Result(undefined, error);  
  }  

  isOk(): this is { value: T } {  
    return this.error === undefined;  
  }  
}  

Application-layer error handling example:

async function processOrder(): Promise<Result<Order, BusinessError>> {  
  try {  
    const order = await repository.fetch();  
    return Result.ok(order);  
  } catch (e) {  
    return Result.fail(  
      e instanceof BusinessError   
        ? e   
        : new SystemError('UNKNOWN_ERROR')  
    );  
  }  
}  

Frontend State Management

Typed Redux solution:

type AppAction =  
  | { type: 'cart/ADD_ITEM'; payload: CartItem }  
  | { type: 'cart/REMOVE_ITEM'; payload: { sku: string } }  
  | { type: 'payment/SET_METHOD'; payload: PaymentMethod };  

function reducer(state: AppState, action: AppAction): AppState {  
  switch (action.type) {  
    case 'cart/ADD_ITEM':  
      return {   
        ...state,  
        cart: [...state.cart, action.payload]  
      };  
    // Other case handlers  
  }  
}  

Enhanced typing for React Context:

interface AuthContextValue {  
  user: User | null;  
  login: (credential: LoginCredential) => Promise<void>;  
  logout: () => void;  
}  

const AuthContext = createContext<AuthContextValue | null>(null);  

function useAuth() {  
  const context = useContext(AuthContext);  
  if (!context) throw new Error('Must be used within AuthProvider');  
  return context;  
}  

Testing Strategy Design

Type-safe test stub implementation:

class MockPaymentService implements PaymentService {  
  private calls: Array<[amount: number, method: string]> = [];  

  async charge(amount: number, method: string) {  
    this.calls.push([amount, method]);  
    return { success: true };  
  }  

  verifyCall(index: number, expected: [number, string]) {  
    const actual = this.calls[index];  
    if (!actual) throw new Error(`No call record found at index ${index}`);  
    expect(actual).toEqual(expected);  
  }  
}  

Type helpers for component testing:

interface TestRendererOptions<Props> {  
  props: Partial<Props>;  
  context?: Partial<AppContext>;  
}  

function renderComponent<Props>(  
  Component: React.FC<Props>,  
  options: TestRendererOptions<Props>  
) {  
  const mergedProps = { ...defaultProps, ...options.props } as Props;  
  // Rendering logic  
}  

Toolchain Integration

Recommended VSCode workspace configuration:

// .vscode/settings.json  
{  
  "typescript.tsdk": "node_modules/typescript/lib",  
  "typescript.enablePromptUseWorkspaceTsdk": true,  
  "eslint.validate": ["typescript", "typescriptreact"],  
  "editor.codeActionsOnSave": {  
    "source.fixAll.eslint": true  
  }  
}  

Example of a custom CLI tool:

import { Command } from 'commander';  
import { analyzeDependencies } from './analyzer';  

const program = new Command();  

program  
  .command('analyze')  
  .option('--depth <number>', 'Dependency analysis depth', '3')  
  .action((options) => {  
    const result = analyzeDependencies(process.cwd(), {  
      depth: parseInt(options.depth)  
    });  
    console.table(result.stats);  
  });  

program.parse();  

Incremental Migration Path

Migration steps for mixed JavaScript projects:

1. Enable allowJs and checkJs in tsconfig.json:

{  
  "compilerOptions": {  
    "allowJs": true,  
    "checkJs": true,  
    "outDir": "./dist"  
  }  
}  

2. Gradually rename files:

# Phase 1: Keep .js extension but enable type checking  
mv utils.js utils.js # Actually add JSDoc comments  

# Phase 2: Change to .ts extension  
mv api-wrapper.js api-wrapper.ts  

3. Type diffusion strategy:

// First declare globally in @types/  
declare global {  
  interface Window {  
    legacyConfig: {  
      apiBase?: string;  
    };  
  }  
}  

// Gradually replace with modular definitions  
interface AppConfig {  
  apiBase: string;  
  env: 'dev' | 'prod';  
}  

Browser Compatibility Solutions

Adjust type definitions based on target environment:

// tsconfig.json  
{  
  "compilerOptions": {  
    "lib": ["es2020", "dom", "dom.iterable"],  
    "target": "es2017",  
    "downlevelIteration": true  
  }  
}  

Handling polyfill type declarations:

interface Array<T> {  
  /**  
   * @polyfill core-js  
   */  
  includes(searchElement: T, fromIndex?: number): boolean;  
}  

if (!Array.prototype.includes) {  
  require('core-js/features/array/includes');  
}  

Type Metaprogramming Techniques

Conditional types for advanced pattern matching:

type ExtractEventNames<T> = T extends { type: infer U } ? U : never;  

type AppEvent =   
  | { type: 'click'; x: number; y: number }  
  | { type: 'scroll'; delta: number };  

type EventNames = ExtractEventNames<AppEvent>; // 'click' | 'scroll'  

Recursive types for complex structures:

type DeepReadonly<T> = {  
  readonly [P in keyof T]: T[P] extends object   
    ? DeepReadonly<T[P]>   
    : T[P];  
};  

interface State {  
  user: {  
    preferences: {  
      theme: string;  
    };  
  };  
}  

type ImmutableState = DeepReadonly<State>;  

Design Pattern Type Implementations

Type-safe factory pattern implementation:

interface Vehicle {  
  move(): void;  
}  

class Car implements Vehicle {  
  move() { console.log('Driving...'); }  
}  

class Truck implements Vehicle {  
  move() { console.log('Hauling...'); }  
}  

type VehicleType = 'car' | 'truck';  

function createVehicle(type: VehicleType): Vehicle {  
  switch (type) {  
    case 'car': return new Car();  
    case 'truck': return new Truck();  
    default:   
      // Type guard ensures this is unreachable  
      const _exhaustiveCheck: never = type;  
      throw new Error(`Unknown type: ${type}`);  
  }  
}  

Generic observer pattern implementation:

type Listener<T> = (event: T) => void;  

class Observable<T> {  
  private listeners: Listener<T>[] = [];  

  subscribe(listener: Listener<T>): () => void {  
    this.listeners.push(listener);  
    return () => {  
      this.listeners = this.listeners.filter(l => l !== listener);  
    };  
  }  

  notify(event: T) {  
    this.listeners.forEach(listener => listener(event));  
  }  
}  

// Usage example  
const clickObservable = new Observable<{ x: number; y: number }>();  
const unsubscribe = clickObservable.subscribe(({ x, y }) => {  
  console.log(`Clicked at (${x}, ${y})`);  
});  

Performance-Sensitive Scenarios

Avoid performance pitfalls with type instantiation:

// Not recommended: Instantiates new types on each call  
function logValue<T>(value: T) {  
  console.log(value);  
}  

// Recommended: Use generic declarations for simple types  
function logValue(value: unknown) {  
  console.log(value);  
}  

Type-safe Web Worker communication wrapper:

// worker-types.ts  
interface WorkerMessage<T extends string, P> {  
  type: T;  
  payload: P;  
}  

type CalculateMessage = WorkerMessage<  
  'CALCULATE',   
  { values: number[] }  
>;  

type ResultMessage = WorkerMessage<  
  'RESULT',  
  { sum: number; product: number }  
>;  

// Main thread usage  
worker.postMessage({  
  type: 'CALCULATE',  
  payload: { values: [1, 2, 3] }  
} as CalculateMessage);  

Compile-Time Validation

Validate formats using template literal types:

type RGBColor = `#${string}`;  

function setBackground(color: RGBColor) {  
  document.body.style.background = color;  
}  

// Correct usage  
setBackground('#ff0000');  

// Compilation error  
setBackground('red');  

Runtime validation with branded types:

interface EmailAddress {  
  readonly __brand: 'EmailAddress';  
}  

function assertValidEmail(str: string): asserts str is EmailAddress {  
  if (!/^[^@]+@[^@]+\.[^@]+$/.test(str)) {  
    throw new Error(`Invalid email: ${str}`);  
  }  
}  

function sendEmail(address: string | EmailAddress) {  
  if (typeof address === 'string') {  
    assertValidEmail(address);  
  }  
  // Here, address is narrowed to EmailAddress type  
  console.log(`Sending to ${address}`);  
}  

Complex State Modeling

Use discriminated union types for state machines:

type AsyncState<T> =  
  | { status: 'idle' }  
  | { status: 'loading'; startTime: number }  
  | { status: 'success'; data: T }  
  | { status: 'error'; error: Error; retryCount: number };  

function render(state: AsyncState<Order[]>) {  
  switch (state.status) {  
    case 'idle':  
      return <button>Load Data</button>;  
    case 'loading':  
      return <Spinner />;  
    case 'success':  
      return <OrderList data={state.data} />;  
    case 'error':  
      return (  
        <div>  
          <ErrorMessage error={state.error} />  
          <button>Retry ({state.retryCount})</button>  
        </div>  
      );  
  }  
}  

Type-Safe International