Skip to main content

Throwing Errors

In JavaScript, you will face situations where something might go wrong and you'd want to handle that error in some way. Throwing errors is one way of handling these unexpected situations. This tutorial will guide you on how to throw errors in JavaScript.

What is Throwing Errors?​

Throwing an error is JavaScript's way of saying "Hey, something is not right here. I can't continue with the execution of this code any further". This is done using the throw statement.

How to Throw Errors?​

Throwing an error in JavaScript is as simple as using the throw keyword followed by an error object. Here's an example:

throw new Error('This is an error message');

When JavaScript encounters this line of code, it creates a new Error object, sets its message property to 'This is an error message', and then "throws" that error.

Types of Errors​

There are several types of error objects you can throw in JavaScript. They are:

  1. Error: a generic error object that you can use for anything.
  2. RangeError: thrown when a number is outside the allowable range of values.
  3. ReferenceError: thrown when trying to use a variable that doesn't exist.
  4. SyntaxError: thrown when trying to execute code with a syntax error.
  5. TypeError: thrown when a variable or parameter is not of a valid type.
  6. URIError: thrown when encodeURI() or decodeURI() are passed invalid parameters.

You can create and throw these errors in the same way as before:

throw new RangeError('Number is out of range');
throw new ReferenceError('Variable does not exist');
throw new SyntaxError('There is a syntax error in your code');
throw new TypeError('Variable or parameter is of invalid type');
throw new URIError('Invalid parameter passed to encodeURI or decodeURI');

Why Throw Errors?​

Throwing errors is beneficial because it helps you to handle exceptions, errors that occur while your program is running, which would otherwise stop your code from executing further.

By throwing an error, you stop the execution of the current function and pass the control to the first catch block in the call stack. If no catch block is found, the program will terminate.

Try-Catch Statement​

The try-catch statement allows you to "catch" errors so you can handle them and prevent the program from crashing. Here's an example:

try {
  // This will throw an error
  throw new Error('This is an error');
} catch(err) {
  // And this will catch the error
  console.error(err);
}

In the above code, if an error is thrown in the try block, the catch block will be executed. The err parameter in the catch block will hold the error object that was thrown.

Conclusion​

Throwing errors is a crucial part of error handling in JavaScript. It allows you to handle problems gracefully and prevent your program from crashing unexpectedly. Always remember to use the try-catch statement when you expect that an error might be thrown.