Error Handling

Why handle errors?

In JavaScript, an error stops code execution.
Without handling, the application can crash unexpectedly.

➡ With try...catch, we intercept errors to handle them gracefully, preventing application crashes.

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try…catch

• try → contains code to execute.
• catch → intercepts errors if they occur.
• finally → always runs (whether an error occurred or not).

try {
  let result = 10 / 0;
  console.log(result);
  throw new Error("Custom error");
} catch (error) {
  console.error("An error occurred:", error.message);
} finally {
  console.log("Finally block executed");
}

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Creating and throwing an error

With throw, you can manually throw an error.

function divide(a, b) {
  if (b === 0) {
    throw new Error("Division by zero is not allowed");
  }
  return a / b;
}

try {
  console.log(divide(10, 0));
} catch (e) {
  console.error(e.message); // Division by zero is not allowed
}

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Custom error types

You can create your own error classes to distinguish cases.

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = "ValidationError";
  }
}

function validateAge(age) {
  if (age < 18) {
    throw new ValidationError("Age is below the allowed limit");
  }
  return true;
}

try {
  validateAge(15);
} catch (e) {
  if (e instanceof ValidationError) {
    console.error("Validation error:", e.message);
  } else {
    console.error("Other error:", e);
  }
}

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Best practices

• Always provide a clear message when throwing errors (throw new Error("...")).
• Use finally to release resources (close file, terminate connection…).
• Create custom error types to better categorize issues.
• Do not overuse try/catch → use them only where an error is likely.