Error Handling

// try — code that might throw an error
// catch — runs if an error occurs in try
// finally — always runs, regardless of success or failure

try {
  const data = JSON.parse(invalidJson);    // throws SyntaxError
  processData(data);
} catch (error) {
  console.error("Parsing failed:", error.message);
  // error.name    — "SyntaxError"
  // error.message — "Unexpected token i in JSON..."
  // error.stack   — full stack trace
} finally {
  console.log("Always runs — cleanup here");
}

// With async/await — wrap in try/catch
async function fetchUser(id) {
  try {
    const response = await fetch(`/api/users/${id}`);

    if (!response.ok) {
      throw new Error(`User ${id} not found (status ${response.status})`);
    }

    return await response.json();
  } catch (error) {
    if (error.name === "TypeError") {
      console.error("Network error — are you offline?", error);
    } else {
      console.error("Fetch error:", error.message);
    }
    return null;  // return a safe fallback
  }
}

// Create custom error classes for meaningful error handling
class ValidationError extends Error {
  constructor(field, message) {
    super(message);
    this.name  = "ValidationError";
    this.field = field;
  }
}

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

try {
  validateEmail("not-an-email");
} catch (error) {
  if (error instanceof ValidationError) {
    console.log(`Field "${error.field}" invalid: ${error.message}`);
  }
}