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How to throw error in JavaScript

Understanding Errors in JavaScript

Before we dive into how to throw errors in JavaScript, it's essential to understand what an error is. You can imagine an error like a red traffic light. It stops the execution of your code and alerts you that something isn't working correctly. It's not bad, but rather, it's an integral part of programming, helping us prevent our code from producing unintended results.

What Does It Mean to 'Throw' an Error?

'Throwing an error' might sound a bit strange if you're new to programming. But don't worry, it's not as complicated as it might sound. In fact, it's just like throwing a ball. When you throw a ball, you're essentially passing it from one place to another. In the same way, when you 'throw' an error in JavaScript, you're passing an error from the place it occurred to a place where it can be handled or 'caught'.

The 'throw' Statement

In JavaScript, we use the throw statement to create custom errors. Let's look at a simple example:

throw 'Error2';   // String type
throw 42;         // Number type
throw true;       // Boolean type
throw {toString: function() { return "I'm an object!"; } };

In the above examples, we're throwing errors of different types: string, number, boolean, and even an object. However, it's best practice to throw an Error object because it captures a stack trace. Stack trace is a report that provides information about the functions that were running when an error occurred. It's like a breadcrumb trail that leads you back to the source of the error.

How to Throw an Error Object

Here's how you can throw an Error object:

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

In the code above, we're creating a new instance of the Error object and passing a string to its constructor. This string is the error message that will be displayed when the error is thrown.

Catching Errors with 'try...catch'

Now that we know how to throw errors, let's look at how to handle them. For this, we use a try...catch statement.

You can think of the try...catch statement as a safety net. When we execute code within the try block, and it throws an error, instead of stopping the entire program, the control is passed to the catch block (the safety net), where the error can be handled.

Here's an example:

try {
  throw new Error('This is an error message');
} catch(e) {
  console.log( + ': ' + e.message);

In the code above, if an error is thrown within the try block, the catch block catches it and handles it by logging the error name and message to the console.

Re-throwing Errors

Sometimes, you might catch an error that you can't handle. In such cases, you can 're-throw' the error. This allows the error to be caught and handled by a higher-level error handler.

Here's how you can do it:

try {
  // code that may throw an error
} catch(e) {
  if (!(e instanceof TypeError)) {
    throw e; // re-throw the error
  // handle the TypeError

In the above code, we're catching an error and checking if it's a TypeError. If it's not, we re-throw the error.

The 'finally' Statement

The finally statement allows you to run code, after try and catch, irrespective of the result. It's like a cleanup crew that comes in after the main event, regardless of whether it was a success or a disaster.

try {
  // code that may throw an error
} catch(e) {
  // handle the error
} finally {
  // code that will run regardless of whether an error was thrown or not


In JavaScript, throwing errors is just as important as writing code. It's a way of communicating with yourself, your team, and your program. It's like driving with a GPS that alerts you when you take a wrong turn, helping you to steer back to the right path. So, don't be afraid to throw errors. Embrace them, catch them, and let them guide you towards better, more reliable code.

Remember, programming isn't just about writing code; it's also about debugging, and understanding how to properly throw and handle errors is an essential part of that process. With the throw, try...catch, and finally statements, you have a robust set of tools at your disposal to manage errors effectively in your JavaScript journey. Happy coding!