Understand Error Objects In JavaScript

In JavaScript, error handling is a critical part of developing robust and reliable applications. Error objects play a significant role in identifying, debugging, and managing errors that occur during the execution of a program.

By learning JavaScript’s built-in error objects and learning how to create and utilize custom error objects, you can significantly improve your debugging capabilities and enhance application stability.

JavaScript’s Built-in Error Objects

JavaScript provides several built-in error objects that represent different types of runtime errors. These error objects can be thrown manually using the throw statement or are automatically generated when a runtime error occurs. Here are some of the most common built-in error objects:

Error: The generic error object and the base type for all other error objects. It indicates that a runtime error has occurred.
TypeError: Indicates that a value is not of the expected type. For example, trying to call something that is not a function.
ReferenceError: Occurs when trying to access a variable that is not defined.
SyntaxError: Thrown when trying to interpret syntactically invalid code.
RangeError: Indicates that a value is not within the expected range. For example, calling a function with fewer arguments than expected.

Each error object contains two main properties:

name: The name of the error (e.g., “TypeError”, “ReferenceError”).
message: A human-readable description of the error.

Example: Throwing a Built-in Error

function checkNumber(num) {
  if (typeof num !== 'number') {
    throw new TypeError('Expected a number but received a ' + typeof num);
  }
  console.log("It's a number:", num);
}

try {
  checkNumber('not a number'); // This will throw a TypeError
} catch (error) {
  console.error(error.name + ': ' + error.message);
}

Creating and Utilizing Custom Error Objects

For more control over error handling, you can create custom error objects by extending the Error class. This is particularly useful for defining application-specific errors.

Creating a Custom Error Object

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

function doSomething() {
  throw new CustomError('This is a custom error message');
}

try {
  doSomething();
} catch (error) {
  console.error(error.name + ': ' + error.message);
}

Custom error objects are invaluable for debugging because they can be tailored to the specific needs of your application, providing clear and detailed information about errors.

Best Practices for Error Handling

Use try...catch blocks to handle errors gracefully and prevent them from crashing your application.
Throw meaningful error messages that accurately describe the issue and how to resolve it.
Consider creating custom error objects for better error categorization and handling in larger applications.
Always log errors, preferably with stack traces, to aid in debugging.