Errors in

About Errors

Errors are useful to report when something is wrong or unexpected in a program or a piece of code.

They are javascript objects.

The main property of this object is message:

const error = new Error('Oops, something went wrong');

console.log(error.message);
// => "Oops, something went wrong"

Using the throw syntax, you can throw an Error.

throw new Error('Oops');

When an error is thrown, the current execution is stopped and resumes in the first catch block of the call stack.

try {
  throw new Error('Oops');
} catch (error) {
  console.log(error.message);
  // => "Oops"
}

As with any class in JavaScript, subclasses can inherit from Error to create Custom errors by using the extends keyword. The instanceof syntax will check if the error caught is an instance of a particular subclass of Error.

class CustomError extends Error {}

try {
  // ... Code that may throw an error
} catch (error) {
  if (error instanceof CustomError) {
    console.log('The error thrown is an instance of the CustomError');
  }
}

Error Types

In addition to the Error object, other built-in error objects exist. You can learn more about it here

Custom Errors

You can also define your own Custom error Type by creating a class that extends one of the built-ins Error Types

class MyCustomError extends Error {}

Throwing non-errors

While the syntax throw is usually used to throw an Error object, JavaScript is flexible and will let you throw a string, a null or any primitive type.

Error stacktraces

While this is not standard in JavaScript, most of the JavaScript environments implement a stack property on the Error objects, allowing you to get the stack trace of the error that was thrown.