Error Handling & Custom Errors

Introduction

Error handling is crucial for building robust applications. TypeScript enhances JavaScript's error handling with type safety, allowing you to create custom error classes and handle errors in a type-safe manner.

Proper error handling helps you:

Identify and fix bugs faster
Provide better user experiences
Make debugging easier
Write more maintainable code

Basic Error Handling

JavaScript Error Handling:

try {
  // Code that might throw
  throw new Error("Something went wrong");
} catch (error) {
  // Handle error
  console.error(error.message);
} finally {
  // Always runs
  console.log("Cleanup");
}

TypeScript Enhanced:

class ValidationError extends Error {
  constructor(
    message: string,
    public field: string
  ) {
    super(message);
    this.name = "ValidationError";
  }
}

try {
  throw new ValidationError("Invalid email", "email");
} catch (error) {
  if (error instanceof ValidationError) {
    console.log(`${error.field}: ${error.message}`);
  } else {
    console.error("Unknown error");
  }
}

Concepts

The Error Class

JavaScript's built-in Error class:

const error = new Error("Something went wrong");
console.log(error.name);     // "Error"
console.log(error.message);  // "Something went wrong"
console.log(error.stack);    // Stack trace

Try-Catch-Finally

function divide(a: number, b: number): number {
  try {
    if (b === 0) {
      throw new Error("Division by zero");
    }
    return a / b;
  } catch (error) {
    console.error("Error:", error);
    return 0;
  } finally {
    console.log("Division attempt completed");
  }
}

console.log(divide(10, 2));  // 5
console.log(divide(10, 0));  // 0 (with error logged)

Custom Error Classes

Create specific error types for different scenarios:

class ValidationError extends Error {
  constructor(
    message: string,
    public field: string,
    public value: any
  ) {
    super(message);
    this.name = "ValidationError";
  
    // Maintains proper stack trace (V8 only)
    if (Error.captureStackTrace) {
      Error.captureStackTrace(this, ValidationError);
    }
  }
}

class NotFoundError extends Error {
  constructor(
    public resourceType: string,
    public resourceId: string | number
  ) {
    super(`${resourceType} with ID ${resourceId} not found`);
    this.name = "NotFoundError";
  }
}

class AuthenticationError extends Error {
  constructor(message: string = "Authentication failed") {
    super(message);
    this.name = "AuthenticationError";
  }
}

// Usage
function validateEmail(email: string): void {
  if (!email.includes("@")) {
    throw new ValidationError(
      "Email must contain @",
      "email",
      email
    );
  }
}

try {
  validateEmail("invalid-email");
} catch (error) {
  if (error instanceof ValidationError) {
    console.log(`Field: ${error.field}`);
    console.log(`Value: ${error.value}`);
    console.log(`Error: ${error.message}`);
  }
}

Type Guards for Errors

function isError(error: unknown): error is Error {
  return error instanceof Error;
}

function isValidationError(error: unknown): error is ValidationError {
  return error instanceof ValidationError;
}

function handleError(error: unknown): void {
  if (isValidationError(error)) {
    console.error(`Validation failed for ${error.field}: ${error.message}`);
  } else if (isError(error)) {
    console.error(`Error: ${error.message}`);
  } else {
    console.error(`Unknown error: ${error}`);
  }
}

Error Handling in Async Functions

async function fetchUser(id: number): Promise<User> {
  try {
    const response = await fetch(`/api/users/${id}`);
  
    if (!response.ok) {
      throw new NotFoundError("User", id);
    }
  
    return await response.json();
  } catch (error) {
    if (error instanceof NotFoundError) {
      console.error(error.message);
      throw error;  // Re-throw if needed
    }
    throw new Error("Failed to fetch user");
  }
}

interface User {
  id: number;
  name: string;
}

Result Type Pattern

Instead of throwing, return success/failure:

Note: In real codebases, teams usually standardise on either throwing exceptions or returning a Result type.
Mixing both styles across an application can make error handling inconsistent, so most teams pick one approach per layer or service.

type Result<T, E = Error> = 
  | { success: true; value: T }
  | { success: false; error: E };

function safeDivide(a: number, b: number): Result<number, string> {
  if (b === 0) {
    return {
      success: false,
      error: "Division by zero"
    };
  }
  
  return {
    success: true,
    value: a / b
  };
}

const result = safeDivide(10, 2);
if (result.success) {
  console.log(result.value);  // 5
} else {
  console.error(result.error);
}

Examples

Form Validation System

class ValidationError extends Error {
  constructor(
    message: string,
    public field: string,
    public value: unknown
  ) {
    super(message);
    this.name = "ValidationError";
  }
}

interface ValidationRule<T> {
  validate: (value: T) => boolean;
  message: string;
}

class Validator {
  static required(fieldName: string): ValidationRule<any> {
    return {
      validate: (value) => value !== null && value !== undefined && value !== "",
      message: `${fieldName} is required`
    };
  }

  static minLength(min: number): ValidationRule<string> {
    return {
      validate: (value) => value.length >= min,
      message: `Must be at least ${min} characters`
    };
  }

  static maxLength(max: number): ValidationRule<string> {
    return {
      validate: (value) => value.length <= max,
      message: `Must be at most ${max} characters`
    };
  }

  static email(): ValidationRule<string> {
    return {
      validate: (value) => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value),
      message: "Must be a valid email"
    };
  }

  static min(min: number): ValidationRule<number> {
    return {
      validate: (value) => value >= min,
      message: `Must be at least ${min}`
    };
  }

  static max(max: number): ValidationRule<number> {
    return {
      validate: (value) => value <= max,
      message: `Must be at most ${max}`
    };
  }
}

function validateField<T>(
  fieldName: string,
  value: T,
  rules: ValidationRule<T>[]
): void {
  for (const rule of rules) {
    if (!rule.validate(value)) {
      throw new ValidationError(rule.message, fieldName, value);
    }
  }
}

// Usage
interface UserForm {
  name: string;
  email: string;
  age: number;
}

function validateUserForm(form: UserForm): void {
  try {
    validateField("name", form.name, [
      Validator.required("Name"),
      Validator.minLength(2),
      Validator.maxLength(50)
    ]);

    validateField("email", form.email, [
      Validator.required("Email"),
      Validator.email()
    ]);

    validateField("age", form.age, [
      Validator.required("Age"),
      Validator.min(18),
      Validator.max(120)
    ]);

    console.log("Form is valid!");
  } catch (error) {
    if (error instanceof ValidationError) {
      console.error(`${error.field}: ${error.message}`);
    }
  }
}

// Test
validateUserForm({
  name: "Alice",
  email: "alice@example.com",
  age: 25
});

validateUserForm({
  name: "B",  // Too short
  email: "invalid-email",
  age: 15  // Too young
});

HTTP Error Hierarchy

class HttpError extends Error {
  constructor(
    message: string,
    public statusCode: number
  ) {
    super(message);
    this.name = "HttpError";
  }
}

class BadRequestError extends HttpError {
  constructor(message: string = "Bad Request") {
    super(message, 400);
    this.name = "BadRequestError";
  }
}

class UnauthorizedError extends HttpError {
  constructor(message: string = "Unauthorized") {
    super(message, 401);
    this.name = "UnauthorizedError";
  }
}

class ForbiddenError extends HttpError {
  constructor(message: string = "Forbidden") {
    super(message, 403);
    this.name = "ForbiddenError";
  }
}

class NotFoundError extends HttpError {
  constructor(message: string = "Not Found") {
    super(message, 404);
    this.name = "NotFoundError";
  }
}

class InternalServerError extends HttpError {
  constructor(message: string = "Internal Server Error") {
    super(message, 500);
    this.name = "InternalServerError";
  }
}

// API Client
class ApiClient {
  async request<T>(endpoint: string): Promise<T> {
    try {
      // Simulate API call
      const statusCode = Math.floor(Math.random() * 500) + 200;
    
      if (statusCode === 400) {
        throw new BadRequestError("Invalid request parameters");
      } else if (statusCode === 401) {
        throw new UnauthorizedError("Please login");
      } else if (statusCode === 403) {
        throw new ForbiddenError("Access denied");
      } else if (statusCode === 404) {
        throw new NotFoundError("Resource not found");
      } else if (statusCode >= 500) {
        throw new InternalServerError("Server error");
      }
    
      return {} as T;
    } catch (error) {
      this.handleError(error);
      throw error;
    }
  }

  private handleError(error: unknown): void {
    if (error instanceof UnauthorizedError) {
      console.log("Redirecting to login...");
    } else if (error instanceof HttpError) {
      console.error(`HTTP ${error.statusCode}: ${error.message}`);
    } else {
      console.error("Unexpected error:", error);
    }
  }
}

// Usage
const client = new ApiClient();

async function fetchData() {
  try {
    await client.request("/api/data");
  } catch (error) {
    if (error instanceof HttpError) {
      console.log(`Failed with status ${error.statusCode}`);
    }
  }
}

Retry Logic with Error Handling

class RetryError extends Error {
  constructor(
    message: string,
    public attempts: number,
    public lastError: Error
  ) {
    super(message);
    this.name = "RetryError";
  }
}

async function retry<T>(
  fn: () => Promise<T>,
  maxAttempts: number = 3,
  delayMs: number = 1000
): Promise<T> {
  let lastError: Error;

  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      return await fn();
    } catch (error) {
      lastError = error instanceof Error ? error : new Error(String(error));
    
      if (attempt === maxAttempts) {
        throw new RetryError(
          `Failed after ${maxAttempts} attempts`,
          maxAttempts,
          lastError
        );
      }
    
      console.log(`Attempt ${attempt} failed, retrying in ${delayMs}ms...`);
      await new Promise(resolve => setTimeout(resolve, delayMs * attempt));
    }
  }
  
  throw new Error("Unexpected error in retry logic");
}

// Usage
async function unreliableOperation(): Promise<string> {
  if (Math.random() > 0.7) {
    return "Success!";
  }
  throw new Error("Operation failed");
}

async function example() {
  try {
    const result = await retry(unreliableOperation, 5, 500);
    console.log(result);
  } catch (error) {
    if (error instanceof RetryError) {
      console.error(`All ${error.attempts} attempts failed`);
      console.error(`Last error: ${error.lastError.message}`);
    }
  }
}

Challenges

1. Custom NotFoundError

Create NotFoundError class
Include resource type and ID
Test with different resources

💡 Show Answer

class NotFoundError extends Error {
  constructor(
    public resourceType: string,
    public resourceId: string | number
  ) {
    super(`${resourceType} with ID ${resourceId} not found`);
    this.name = "NotFoundError";
  }
}

function findUser(id: number): void {
  throw new NotFoundError("User", id);
}

function findProduct(id: string): void {
  throw new NotFoundError("Product", id);
}

try {
  findUser(123);
} catch (error) {
  if (error instanceof NotFoundError) {
    console.log(`Resource: ${error.resourceType}`);
    console.log(`ID: ${error.resourceId}`);
    console.log(`Message: ${error.message}`);
  }
}

2. Safe Division Function

Function that doesn't throw
Returns Result type
Handle division by zero

💡 Show Answer

type Result<T, E> = 
  | { success: true; value: T }
  | { success: false; error: E };

function safeDivide(a: number, b: number): Result<number, string> {
  if (b === 0) {
    return {
      success: false,
      error: "Cannot divide by zero"
    };
  }
  
  if (!Number.isFinite(a) || !Number.isFinite(b)) {
    return {
      success: false,
      error: "Arguments must be finite numbers"
    };
  }
  
  return {
    success: true,
    value: a / b
  };
}

// Usage
const result1 = safeDivide(10, 2);
if (result1.success) {
  console.log(`Result: ${result1.value}`);  // 5
}

const result2 = safeDivide(10, 0);
if (!result2.success) {
  console.error(`Error: ${result2.error}`);  // Cannot divide by zero
}

const result3 = safeDivide(10, Infinity);
if (!result3.success) {
  console.error(`Error: ${result3.error}`);
}

3. Email Validator

Throw ValidationError on invalid email
Include field name and value
Test with various inputs

💡 Show Answer

class ValidationError extends Error {
  constructor(
    message: string,
    public field: string,
    public value: any
  ) {
    super(message);
    this.name = "ValidationError";
  }
}

function validateEmail(email: string): void {
  if (!email || email.trim() === "") {
    throw new ValidationError(
      "Email cannot be empty",
      "email",
      email
    );
  }

  if (!email.includes("@")) {
    throw new ValidationError(
      "Email must contain @ symbol",
      "email",
      email
    );
  }

  if (!email.includes(".")) {
    throw new ValidationError(
      "Email must contain a domain",
      "email",
      email
    );
  }

  const [local, domain] = email.split("@");

  if (!local || local.length === 0) {
    throw new ValidationError(
      "Email must have a local part before @",
      "email",
      email
    );
  }

  if (!domain || domain.length === 0) {
    throw new ValidationError(
      "Email must have a domain after @",
      "email",
      email
    );
  }
}

// Test cases
const testEmails = [
  "valid@example.com",
  "invalid",
  "@example.com",
  "user@",
  "",
  "no-at-sign.com"
];

testEmails.forEach(email => {
  try {
    validateEmail(email);
    console.log(`✓ ${email} is valid`);
  } catch (error) {
    if (error instanceof ValidationError) {
      console.log(`✗ ${email}: ${error.message}`);
    }
  }
});

4. Try-Catch Wrapper

Create utility to wrap functions
Return Result type instead of throwing
Handle any errors

💡 Show Answer

type Result<T, E = Error> = 
  | { success: true; value: T }
  | { success: false; error: E };

function tryCatch<T>(fn: () => T): Result<T, Error> {
  try {
    const value = fn();
    return { success: true, value };
  } catch (error) {
    return {
      success: false,
      error: error instanceof Error ? error : new Error(String(error))
    };
  }
}

async function tryCatchAsync<T>(
  fn: () => Promise<T>
): Promise<Result<T, Error>> {
  try {
    const value = await fn();
    return { success: true, value };
  } catch (error) {
    return {
      success: false,
      error: error instanceof Error ? error : new Error(String(error))
    };
  }
}

// Usage
const result1 = tryCatch(() => {
  return JSON.parse('{"name":"Alice"}');
});

if (result1.success) {
  console.log(result1.value);
}

const result2 = tryCatch(() => {
  return JSON.parse('invalid json');
});

if (!result2.success) {
  console.error(result2.error.message);
}

// Async example
async function example() {
  const result = await tryCatchAsync(async () => {
    const response = await fetch("/api/data");
    return response.json();
  });
  
  if (result.success) {
    console.log(result.value);
  } else {
    console.error(result.error);
  }
}

5. Error Logger

Log errors with timestamp
Different log levels
Store error history

💡 Show Answer

type LogLevel = "info" | "warn" | "error";

interface LogEntry {
  level: LogLevel;
  message: string;
  error?: Error;
  timestamp: Date;
}

class ErrorLogger {
  private logs: LogEntry[] = [];

  log(level: LogLevel, message: string, error?: Error): void {
    const entry: LogEntry = {
      level,
      message,
      error,
      timestamp: new Date()
    };

    this.logs.push(entry);

    const prefix =`[${level.toUpperCase()}] ${entry.timestamp.toISOString()}`;

    if (error) {
      console.log(`${prefix} ${message}:`);
      console.log(error);
    } else {
      console.log(`${prefix} ${message}`);
    }
  }

  info(message: string): void {
    this.log("info", message);
  }

  warn(message: string, error?: Error): void {
    this.log("warn", message, error);
  }

  error(message: string, error: Error): void {
    this.log("error", message, error);
  }

  getHistory(): LogEntry[] {
    return [...this.logs];
  }

  getErrorCount(): number {
    return this.logs.filter(log => log.level === "error").length;
  }

  clear(): void {
    this.logs = [];
  }
}

// Usage
const logger = new ErrorLogger();

logger.info("Application started");

try {
  throw new Error("Something went wrong");
} catch (error) {
  if (error instanceof Error) {
    logger.error("Operation failed", error);
  }
}

logger.warn("Low memory");

console.log("\nError count:", logger.getErrorCount());
console.log("Log history:", logger.getHistory());

6. Async Error Handler

Handle async function errors
Retry on failure
Log attempts

💡 Show Answer

async function handleAsync<T>(
  fn: () => Promise<T>,
  maxRetries: number = 3
): Promise<T> {
  let lastError: Error;

  for (let attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      console.log(`Attempt ${attempt}/${maxRetries}`);
      return await fn();
    } catch (error) {
      lastError = error instanceof Error ? error : new Error(String(error));
      console.log(`Attempt ${attempt} failed: ${lastError.message}`);
    
      if (attempt < maxRetries) {
        const delay = 1000 * attempt;
        console.log(`Waiting ${delay}ms before retry...`);
        await new Promise(resolve => setTimeout(resolve, delay));
      }
    }
  }
  
  throw new Error(`Failed after ${maxRetries} attempts: ${lastError!.message}`);
}

// Usage
async function unreliableFunction(): Promise<string> {
  if (Math.random() > 0.6) {
    return "Success!";
  }
  throw new Error("Random failure");
}

async function example() {
  try {
    const result = await handleAsync(unreliableFunction, 5);
    console.log("Final result:", result);
  } catch (error) {
    console.error("All attempts failed:", error);
  }
}

example();

7. Multiple Error Types

Handle different error types differently
DatabaseError, NetworkError, ValidationError
Appropriate handling for each

💡 Show Answer

class DatabaseError extends Error {
  constructor(
    message: string,
    public query: string
  ) {
    super(message);
    this.name = "DatabaseError";
  }
}

class NetworkError extends Error {
  constructor(
    message: string,
    public url: string,
    public statusCode?: number
  ) {
    super(message);
    this.name = "NetworkError";
  }
}

class ValidationError extends Error {
  constructor(
    message: string,
    public field: string
  ) {
    super(message);
    this.name = "ValidationError";
  }
}

function handleError(error: unknown): void {
  if (error instanceof DatabaseError) {
    console.error(`Database error: ${error.message}`);
    console.error(`Query: ${error.query}`);
    // Maybe retry or use cached data
  } else if (error instanceof NetworkError) {
    console.error(`Network error: ${error.message}`);
    console.error(`URL: ${error.url}`);
    if (error.statusCode) {
      console.error(`Status: ${error.statusCode}`);
    }
    // Maybe retry request
  } else if (error instanceof ValidationError) {
    console.error(`Validation error in ${error.field}: ${error.message}`);
    // Show user feedback
  } else if (error instanceof Error) {
    console.error(`Unknown error: ${error.message}`);
  } else {
    console.error(`Unexpected error: ${error}`);
  }
}

// Test
try {
  throw new DatabaseError("Connection failed", "SELECT * FROM users");
} catch (error) {
  handleError(error);
}

try {
  throw new NetworkError("Timeout", "https://api.example.com", 408);
} catch (error) {
  handleError(error);
}

try {
  throw new ValidationError("Invalid email format", "email");
} catch (error) {
  handleError(error);
}

8. Error Boundary Class

Catch and handle errors in operations
Provide fallback values
Log all errors

💡 Show Answer

class ErrorBoundary<T> {
  private errorLog: Error[] = [];

  execute(
    operation: () => T,
    fallback: T
  ): T {
    try {
      return operation();
    } catch (error) {
      const err = error instanceof Error ? error : new Error(String(error));
      this.errorLog.push(err);
      console.error(`Error caught: ${err.message}`);
      return fallback;
    }
  }

  async executeAsync(
    operation: () => Promise<T>,
    fallback: T
  ): Promise<T> {
    try {
      return await operation();
    } catch (error) {
      const err = error instanceof Error ? error : new Error(String(error));
      this.errorLog.push(err);
      console.error(`Error caught: ${err.message}`);
      return fallback;
    }
  }

  getErrors(): Error[] {
    return [...this.errorLog];
  }

  clearErrors(): void {
    this.errorLog = [];
  }

  hasErrors(): boolean {
    return this.errorLog.length > 0;
  }
}

// Usage
const boundary = new ErrorBoundary<number>();

const result1 = boundary.execute(() => {
  return JSON.parse('{"value": 42}').value;
}, 0);
console.log(result1);  // 42

const result2 = boundary.execute(() => {
  return JSON.parse('invalid').value;
}, 0);
console.log(result2);  // 0 (fallback)

console.log("Has errors:", boundary.hasErrors());
console.log("Error count:", boundary.getErrors().length);

9. Error Chain

Track error chain/cause
Show full error context
Nested error handling

💡 Show Answer

class ChainedError extends Error {
  constructor(
    message: string,
    public cause?: Error
  ) {
    super(message);
    this.name = "ChainedError";
  }

  getFullMessage(): string {
    let message = this.message;
    let current: Error | undefined = this.cause;

    while (current) {
      message +=`\n  Caused by: ${current.message}`;
      current = current instanceof ChainedError ? current.cause : undefined;
    }

    return message;
  }

  getCauseChain(): Error[] {
    const chain: Error[] = [this];
    let current: Error | undefined = this.cause;

    while (current) {
      chain.push(current);
      current = current instanceof ChainedError ? current.cause : undefined;
    }

    return chain;
  }
}

// Example
function level3Operation(): void {
  throw new Error("Database connection failed");
}

function level2Operation(): void {
  try {
    level3Operation();
  } catch (error) {
    throw new ChainedError(
      "Failed to fetch user data",
      error instanceof Error ? error : new Error(String(error))
    );
  }
}

function level1Operation(): void {
  try {
    level2Operation();
  } catch (error) {
    throw new ChainedError(
      "Failed to load dashboard",
      error instanceof Error ? error : new Error(String(error))
    );
  }
}

// Test
try {
  level1Operation();
} catch (error) {
  if (error instanceof ChainedError) {
    console.log(error.getFullMessage());
    console.log("\nChain length:", error.getCauseChain().length);
  }
}

10. Safe JSON Parser

Parse JSON safely
Return Result type
Include parsing error details

💡 Show Answer

type ParseResult<T> = 
  | { success: true; data: T }
  | { success: false; error: string; position?: number };

function safeJsonParse<T>(json: string): ParseResult<T> {
  try {
    const data = JSON.parse(json) as T;
    return { success: true, data };
  } catch (error) {
    let errorMessage = "Invalid JSON";
    let position: number | undefined;
  
    if (error instanceof SyntaxError) {
      errorMessage = error.message;
    
      // Try to extract position from error message
      const match = error.message.match(/position (\d+)/);
      if (match) {
        position = parseInt(match[1], 10);
      }
    }
  
    return {
      success: false,
      error: errorMessage,
      position
    };
  }
}

// Usage
const validJson = '{"name":"Alice","age":30}';
const invalidJson = '{"name":"Bob",age:25}';  // Missing quotes around 'age'

const result1 = safeJsonParse(validJson);
if (result1.success) {
  console.log("Parsed:", result1.data);
}

const result2 = safeJsonParse(invalidJson);
if (!result2.success) {
  console.error("Parse error:", result2.error);
  if (result2.position !== undefined) {
    console.error("At position:", result2.position);
  }
}

// With type checking
interface User {
  name: string;
  age: number;
}

function isUser(obj: any): obj is User {
  return (
    typeof obj === "object" &&
    typeof obj.name === "string" &&
    typeof obj.age === "number"
  );
}

function parseUser(json: string): ParseResult<User> {
  const result = safeJsonParse<User>(json);
  
  if (!result.success) {
    return result;
  }
  
  if (!isUser(result.data)) {
    return {
      success: false,
      error: "Invalid user structure"
    };
  }
  
  return result;
}

const userResult = parseUser('{"name":"Charlie","age":35}');
if (userResult.success) {
  console.log(`User: ${userResult.data.name}, Age: ${userResult.data.age}`);
}

Summary

In this chapter, you learned:

✅ Try-catch-finally error handling

✅ Creating custom error classes

✅ Error type hierarchies

✅ Type guards for errors

✅ Async error handling

✅ Result type pattern

✅ Error logging and tracking

✅ Retry logic

Key Takeaways:

Extend Error class for custom errors
Use meaningful error names and messages
Include relevant context in custom errors
Handle errors at appropriate levels
Use type guards to identify error types
Consider Result type instead of throwing
Log errors for debugging

Best Practices:

Create specific error types for different scenarios
Include context (field names, IDs, etc.)
Use Error.captureStackTrace for better stack traces
Handle errors close to where they occur
Re-throw if you can't handle the error
Always clean up in finally blocks
Log errors for monitoring

Common Patterns:

Validation errors with field context
HTTP errors with status codes
Not found errors with resource info
Authentication/authorization errors
Database/network errors
Retry logic with exponential backoff
Error boundaries for graceful degradation

In the next chapter, we'll explore Testing with Jest !

Continue to Chapter 17: Testing with Jest →

Introduction​

Basic Error Handling​

Concepts​

The Error Class​

Try-Catch-Finally​

Custom Error Classes​

Type Guards for Errors​

Error Handling in Async Functions​

Result Type Pattern​

Examples​

Form Validation System​

HTTP Error Hierarchy​

Retry Logic with Error Handling​

Challenges​

1. Custom NotFoundError​

2. Safe Division Function​

3. Email Validator​

4. Try-Catch Wrapper​

5. Error Logger​

6. Async Error Handler​

7. Multiple Error Types​

8. Error Boundary Class​

9. Error Chain​

10. Safe JSON Parser​

Summary​

Introduction

Basic Error Handling

Concepts

The Error Class

Try-Catch-Finally

Custom Error Classes

Type Guards for Errors

Error Handling in Async Functions

Result Type Pattern

Examples

Form Validation System

HTTP Error Hierarchy

Retry Logic with Error Handling

Challenges

1. Custom NotFoundError

2. Safe Division Function

3. Email Validator

4. Try-Catch Wrapper

5. Error Logger

6. Async Error Handler

7. Multiple Error Types

8. Error Boundary Class

9. Error Chain

10. Safe JSON Parser

Summary