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ISA-Frontend/docs/guidelines/code-style.md
2025-04-28 15:36:03 +00:00

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# Code Style Guidelines
## General Principles
- **Readability First**: Write code that is easy to read and understand.
- **Consistency**: Follow the same patterns and conventions throughout the codebase.
- **Clean Code**: Avoid unnecessary complexity and keep functions small and focused.
- **SOLID Principles**: Follow SOLID design principles to create more maintainable, flexible, and scalable code.
## SOLID Design Principles
SOLID is an acronym for five design principles that help make software designs more understandable, flexible, and maintainable:
- **Single Responsibility Principle (SRP)**: A class should have only one reason to change, meaning it should have only one job or responsibility.
```typescript
// Good - Each class has a single responsibility
class UserAuthentication {
authenticate(username: string, password: string): boolean {
// Authentication logic
}
}
class UserRepository {
findById(id: string): User {
// Database access logic
}
}
// Bad - Class has multiple responsibilities
class UserManager {
authenticate(username: string, password: string): boolean {
// Authentication logic
}
findById(id: string): User {
// Database access logic
}
sendEmail(user: User, message: string): void {
// Email sending logic
}
}
```
- **Open/Closed Principle (OCP)**: Software entities should be open for extension but closed for modification.
```typescript
// Good - Open for extension
interface PaymentProcessor {
processPayment(amount: number): void;
}
class CreditCardProcessor implements PaymentProcessor {
processPayment(amount: number): void {
// Credit card processing logic
}
}
class PayPalProcessor implements PaymentProcessor {
processPayment(amount: number): void {
// PayPal processing logic
}
}
// New payment methods can be added without modifying existing code
```
- **Liskov Substitution Principle (LSP)**: Objects of a superclass should be replaceable with objects of subclasses without affecting the correctness of the program.
```typescript
// Good - Derived classes can substitute base class
class Rectangle {
constructor(
protected width: number,
protected height: number,
) {}
setWidth(width: number): void {
this.width = width;
}
setHeight(height: number): void {
this.height = height;
}
getArea(): number {
return this.width * this.height;
}
}
class Square extends Rectangle {
constructor(size: number) {
super(size, size);
}
// Preserve behavior when overriding methods
setWidth(width: number): void {
super.setWidth(width);
super.setHeight(width);
}
setHeight(height: number): void {
super.setWidth(height);
super.setHeight(height);
}
}
```
- **Interface Segregation Principle (ISP)**: Clients should not be forced to depend on interfaces they do not use.
```typescript
// Good - Segregated interfaces
interface Printable {
print(): void;
}
interface Scannable {
scan(): void;
}
class AllInOnePrinter implements Printable, Scannable {
print(): void {
// Printing logic
}
scan(): void {
// Scanning logic
}
}
class BasicPrinter implements Printable {
print(): void {
// Printing logic
}
}
// Bad - Fat interface
interface OfficeMachine {
print(): void;
scan(): void;
fax(): void;
staple(): void;
}
// Classes must implement methods they don't need
```
- **Dependency Inversion Principle (DIP)**: High-level modules should not depend on low-level modules. Both should depend on abstractions.
```typescript
// Good - Depending on abstractions
interface Logger {
log(message: string): void;
}
class ConsoleLogger implements Logger {
log(message: string): void {
console.log(message);
}
}
class FileLogger implements Logger {
log(message: string): void {
// File logging logic
}
}
class UserService {
constructor(private logger: Logger) {}
createUser(user: User): void {
// Create user logic
this.logger.log(`User created: ${user.name}`);
}
}
// The UserService depends on the abstraction (Logger interface)
// not on concrete implementations
```
Following these principles improves code quality by:
- Reducing coupling between components
- Making the system more modular and easier to maintain
- Facilitating testing and extension
- Promoting code reuse
## Extended Guidelines for Angular and TypeScript
This section extends the core code style principles with Angular-specific and advanced TypeScript best practices to ensure consistency and maintainability in our projects.
### Angular Enhancements
- **Change Detection**: Use the OnPush strategy by default for better performance.
- **Lifecycle Hooks**: Explicitly implement Angular lifecycle interfaces (OnInit, OnDestroy, etc.).
- **Template Management**: Keep templates concise and use the async pipe to handle observables.
- **Component Structure**: Follow best practices for component modularization to enhance readability and testability.
- **Naming Conventions**: Follow Angular's official naming conventions for selectors, files, and component classes.
- **File Organization**: Structure files according to features and follow the recommended folder structure.
- **Control Flow**: Use modern control flow syntax (@if, @for) instead of structural directives (*ngIf, *ngFor).
- **Signals**: Prefer signals over RxJS for simpler state management within components.
- **Standalone by Default**: Components and directives are standalone by default. The `standalone: true` flag is unnecessary. Only specify `standalone: false` when a component or directive explicitly needs to be part of an NgModule.
### TypeScript Enhancements
- **Strict Type Checking**: Enable strict mode (`strict: true`) and avoid excessive use of `any`.
- **Interfaces vs. Types**: Prefer interfaces for object definitions and use type aliases for unions and intersections.
- **Generics**: Use meaningful type parameter names and constrain generics when applicable.
- **Documentation**: Employ JSDoc comments for functions and generic parameters to improve code clarity.
- **Non-Nullability**: Use the non-null assertion operator (!) sparingly and only when you're certain a value cannot be null.
- **Type Guards**: Implement custom type guards to handle type narrowing safely.
- **Immutability**: Favor immutable data structures and use readonly modifiers when applicable.
- **Exhaustiveness Checking**: Use exhaustiveness checking for switch statements handling union types.
## TypeScript Guidelines
- **Strict Typing**:
- Enable `strict: true` in tsconfig.json
- Avoid `any` unless absolutely necessary
- Use `unknown` instead of `any` when type is truly unknown
- Always specify return types for functions
- Use type inference for variable declarations where types are obvious
```typescript
// Good
const user: User = getUserById('123');
const items = ['apple', 'banana']; // Type inference is fine here
// Bad
const user: any = getUserById('123');
const items: string[] = ['apple', 'banana']; // Unnecessary type annotation
```
- **Interfaces and Types**:
- Prefer `interface` over `type` for object definitions
- Use `type` for unions, intersections, and mapped types
- Follow Angular's naming convention: Don't prefix interfaces with 'I' (use `ComponentProps` not `IComponentProps`)
- Extend interfaces instead of repeating properties
- Use readonly modifiers where appropriate
```typescript
// Good
interface BaseProps {
readonly id: string;
name: string;
}
interface UserProps extends BaseProps {
email: string;
}
type ValidationResult = 'success' | 'error' | 'pending';
// Bad
type UserProps = {
id: string;
name: string;
email: string;
};
```
- **Enums and Constants**:
- Prefer this order of implementation (from most to least preferred):
1. `const enum` for better compile-time performance
2. Object literals with `as const` for runtime flexibility
3. Regular `enum` only when necessary for runtime access
- **When to use each approach**:
- Use `const enum` for internal application enumerations that don't need runtime access
- Use `const object as const` when values need to be inspected at runtime or exported in an API
- Use regular `enum` only when runtime enumeration object access is required
```typescript
// Good - const enum (preferred for most cases)
// Advantages: Tree-shakable, type-safe, disappears at compile time
export const enum ConstEnumStates {
NotSet = 'not-set',
Success = 'success',
}
// Good - const object with 'as const' assertion
// Advantages: Runtime accessible, works well with API boundaries
export const ConstStates = {
NotSet: 'not-set',
Success: 'success',
} as const;
// Types can be extracted from const objects
type ConstStatesType = (typeof ConstStates)[keyof typeof ConstStates];
// Least preferred - regular enum
// Only use when you need the enum object at runtime
export enum States {
NotSet = 'not-set',
Success = 'success',
}
```
- Use union types as an alternative for simple string literals
```typescript
// Alternative approach using union types
export type StatusType = 'not-set' | 'success';
```
- **Functions and Methods**:
- Always export functions as arrow function expressions (const) instead of function declarations
- Use arrow functions for callbacks and class methods
- Explicitly type parameters and return values
- Keep functions pure when possible
- Use function overloads for complex type scenarios
- Document complex functions with JSDoc
```typescript
// Good
/**
* Fetches a user by ID and transforms it to the required format
* @param id - The user's unique identifier
* @param includeDetails - Whether to include additional user details
*/
export const getUser = (id: string, includeDetails = false): Promise<User> => {
// ...implementation
};
// Bad
export function getUser(id) {
// ...implementation
}
```
// Reason for using arrow function expressions:
// 1. More consistent with modern JavaScript practices
// 2. Easier to mock in unit tests
// 3. Avoids 'this' binding issues
- **Generics**:
- Use meaningful type parameter names (e.g., `T` for type, `K` for key)
- Constrain generic types when possible using `extends`
- Document generic parameters using JSDoc
Example:
```typescript
// Good
interface UserProps {
id: string;
name: string;
}
interface AdminProps extends UserProps {
permissions: string[];
}
const enum UserRole {
Admin = 'ADMIN',
User = 'USER',
}
const getUser = <T extends UserProps>(id: string): Promise<T> => {
// ...implementation
};
// Bad
type User = {
id: any;
name: any;
};
function getUser(id) {
// ...implementation
}
```
## Angular-Specific Guidelines
- **Components**:
- Use OnPush change detection strategy by default
- Implement lifecycle hooks interfaces explicitly
- Keep templates small and focused
- Use async pipe instead of manual subscription management
```typescript
// Good
@Component({
selector: 'app-user-list',
changeDetection: ChangeDetectionStrategy.OnPush,
})
export class UserListComponent implements OnInit, OnDestroy {
users$ = this.userService.getUsers().pipe(shareReplay(1));
}
// Bad
@Component({
selector: 'app-user-list',
})
export class UserListComponent {
users: User[] = [];
subscription: Subscription;
ngOnInit() {
this.subscription = this.userService
.getUsers()
.subscribe((users) => (this.users = users));
}
}
```
- **Templates and Control Flow**:
- Use modern control flow syntax (`@if`, `@for`, `@switch`) instead of structural directives (`*ngIf`, `*ngFor`, `*ngSwitch`).
```html
<!-- Good - Modern control flow syntax -->
<div>
@if (user) {
<h1>Welcome, {{ user.name }}!</h1>
} @else if (isLoading) {
<h1>Loading user data...</h1>
} @else {
<h1>Please log in</h1>
}
<ul>
@for (item of items; track item.id) {
<li>{{ item.name }}</li>
} @empty {
<li>No items available</li>
}
</ul>
@switch (userRole) { @case ('admin') {
<app-admin-dashboard />
} @case ('manager') {
<app-manager-dashboard />
} @default {
<app-user-dashboard />
} }
</div>
<!-- Bad - Old structural directives -->
<div>
<h1 *ngIf="user">Welcome, {{ user.name }}!</h1>
<h1 *ngIf="!user && isLoading">Loading user data...</h1>
<h1 *ngIf="!user && !isLoading">Please log in</h1>
<ul>
<li *ngFor="let item of items; trackBy: trackById">{{ item.name }}</li>
<li *ngIf="!items || items.length === 0">No items available</li>
</ul>
<app-admin-dashboard *ngIf="userRole === 'admin'"></app-admin-dashboard>
<app-manager-dashboard
*ngIf="userRole === 'manager'"
></app-manager-dashboard>
<app-user-dashboard
*ngIf="userRole !== 'admin' && userRole !== 'manager'"
></app-user-dashboard>
</div>
```
- When using `@for`, always specify the `track` expression to optimize rendering performance:
- Use a unique identifier property (like `id` or `uuid`) when available
- Only use `$index` for static collections that never change
- Avoid using non-unique properties that could result in DOM mismatches
- Leverage contextual variables in `@for` blocks:
- `$index` - Current item index
- `$first` - Boolean indicating if this is the first item
- `$last` - Boolean indicating if this is the last item
- `$even` - Boolean indicating if this index is even
- `$odd` - Boolean indicating if this index is odd
- `$count` - Total number of items in the collection
```html
<!-- Good - Using contextual variables -->
@for (item of items; track item.id; let i = $index, isLast = $last) {
<li [class.last-item]="isLast">{{ i + 1 }}. {{ item.name }}</li>
}
```
- Use the `@empty` block with `@for` to handle empty collections gracefully
- Store conditional expression results in variables for clearer templates:
```html
<!-- Good - Storing expression result in variable -->
@if (user.permissions.canEditSettings; as canEdit) {
<button [disabled]="!canEdit">Edit Settings</button>
}
```
## Error Logging
Proper error logging is critical for diagnosing issues in production applications. Always use the `@isa/core/logging` module for logging throughout the application.
### Basic Logging Guidelines
- Always use the appropriate log level for the situation:
- `trace` - For fine-grained debugging information
- `debug` - For development-time debugging information
- `info` - For general runtime information
- `warn` - For potential issues that don't interrupt operation
- `error` - For errors that affect functionality
### Setting Up Logging
Use the logger factory function to create loggers in your components and services:
```typescript
import { logger } from '@isa/core/logging';
@Component({
selector: 'app-example',
templateUrl: './example.component.html',
})
export class ExampleComponent implements OnInit {
// Create a private logger instance
#logger = logger();
constructor(private userService: UserService) {}
ngOnInit(): void {
this.#logger.info('Component initialized');
}
}
```
### Context-Aware Logging
Always provide relevant context when logging:
```typescript
// Good - With detailed context
this.#logger.error(
'Failed to load user data',
error,
{ userId: '123', attempt: 2, source: 'UserProfileComponent' }
);
// Bad - No context for troubleshooting
this.#logger.error('Failed to load user data');
```
### Component and Service Level Context
Use the `provideLoggerContext` to set component-level context:
```typescript
@Component({
selector: 'app-user-profile',
templateUrl: './user-profile.component.html',
providers: [
provideLoggerContext({
component: 'UserProfile',
section: 'Account'
})
]
})
export class UserProfileComponent {
#logger = logger();
// All logs from this component will include the context
updateProfile(): void {
this.#logger.info('Updating user profile');
// Log output will include { component: 'UserProfile', section: 'Account' }
}
}
```
### Error Handling Best Practices
1. **Always log the original Error object**:
```typescript
// Good - Includes the original error with stack trace
try {
// risky operation
} catch (error) {
this.#logger.error('Operation failed', error, { context: 'additional data' });
}
// Bad - Loses the stack trace and error details
try {
// risky operation
} catch (error) {
this.#logger.error(`Operation failed: ${error}`);
}
```
2. **Structure error handling with contextual information**:
```typescript
saveData(data: UserData): void {
this.userService.save(data).pipe(
catchError((error) => {
this.#logger.error(
'Failed to save user data',
error,
{
userId: data.id,
dataSize: JSON.stringify(data).length,
operation: 'saveData'
}
);
// Handle the error appropriately
return throwError(() => new Error('Failed to save data'));
})
).subscribe();
}
```
3. **Use log levels appropriately**:
```typescript
// Debug information during development
this.#logger.debug('Processing data batch', { batchSize: items.length });
// General information during runtime
this.#logger.info('User logged in', { userId: user.id });
// Potential issues that don't break functionality
this.#logger.warn('API response slow', { responseTime: '2500ms', endpoint: '/users' });
// Errors that affect functionality
this.#logger.error('Payment processing failed', error, { orderId: order.id });
```
4. **In RxJS operators, use tap for logging**:
```typescript
return this.http.get<User[]>('/api/users').pipe(
tap({
next: (users) => this.#logger.info('Users loaded', { count: users.length }),
error: (error) => this.#logger.error('Failed to load users', error)
}),
catchError((error) => {
this.#logger.error('Error in users API call', error, { retry: true });
return this.fallbackUserService.getUsers();
})
);
```
5. **Log lifecycle events when relevant**:
```typescript
export class ImportantComponent implements OnInit, OnDestroy {
#logger = logger();
ngOnInit(): void {
this.#logger.debug('Component initialized');
}
ngOnDestroy(): void {
this.#logger.debug('Component destroyed');
}
}
```
### Performance Considerations
- Avoid expensive operations in log messages in production:
```typescript
// Bad - Performs expensive operation even if debug level is disabled
this.#logger.debug('Data state:', JSON.stringify(this.largeDataObject));
// Good - Only performs expensive operation if needed
if (isDevMode()) {
this.#logger.debug('Data state:', { data: this.largeDataObject });
}
```
- Consider log level in production environments:
```typescript
// In app.config.ts
export const appConfig: ApplicationConfig = {
providers: [
// Other providers...
provideLogging(
withLogLevel(isDevMode() ? LogLevel.Debug : LogLevel.Warn),
withSink(ConsoleLogSink)
)
]
};
```
## Project-Specific Preferences
- **Frameworks**: Follow best practices for Nx, Angular, date-fns, Ngrx, RxJs and Zod.
- **Testing**: Use Jest with Spectator for unit tests and follow the Arrange-Act-Assert pattern.
- **File Naming**:
- Use kebab-case for filenames (e.g., `my-component.ts`).
- Follow a pattern that describes the symbol's feature then its type: `feature.type.ts`
```
// Good examples
user.service.ts
auth.guard.ts
product-list.component.ts
order.model.ts
// Bad examples
service-user.ts
userService.ts
```
- **Comments**: Use JSDoc for documenting functions, classes, and modules.
## Formatting
- **Indentation**: Use 2 spaces for indentation.
- **Line Length**: Limit lines to 80 characters where possible.
- **Semicolons**: Always use semicolons.
- **Quotes**: Use single quotes for strings, except when using template literals.
## Linting and Tools
- Use ESLint with the recommended TypeScript and Nx configurations.
- Prettier should be used for consistent formatting.
## References
- [Angular Style Guide](https://angular.dev/style-guide) - Official Angular style guide with best practices for Angular development
- [Angular Control Flow](https://angular.dev/guide/templates/control-flow) - Official Angular documentation on the new control flow syntax (@if, @for, @switch)
- [TypeScript Style Guide](https://ts.dev/style/) - TypeScript community style guide with patterns and practices
- [SOLID Design Principles](https://en.wikipedia.org/wiki/SOLID) - Wikipedia article explaining the SOLID principles in object-oriented design
- [Clean Code](https://www.amazon.com/Clean-Code-Handbook-Software-Craftsmanship/dp/0132350882) - Robert C. Martin's seminal book on writing clean, maintainable code