Introduction

This tutorial is designed to provide you with an understanding of how to handle errors in TypeScript, a statically typed superset of JavaScript. Error handling is a crucial part of any application and TypeScript provides robust tools to manage and anticipate errors in your code.

By the end of this tutorial, you will be able to:

• Use try-catch statements to handle runtime errors.
• Define custom error classes.
• Work with error interfaces.

Prerequisites: You should have a basic understanding of JavaScript and TypeScript.

Step-by-Step Guide

Try-Catch Statement

A try-catch statement in TypeScript is used to handle runtime errors. The try block contains the code that might throw an exception, and the catch block is used to handle the exception if one occurs.

Here's an example:

try {
  // code that might throw an exception
} catch (error) {
  // handle the error
}

It's a best practice to throw an instance of Error or a subclass of Error, as it makes it easier to handle specific error types using instanceof in a catch block.

Custom Error Classes

In TypeScript, you can create custom error classes by extending the built-in Error class. Custom error classes can be used to throw and catch specific errors.

Here's an example of a custom error class:

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

Error Interfaces

In TypeScript, an interface can also be used to define the shape of an error. This can be particularly useful when working with libraries or APIs that define their own error structures.

Here's an example of an error interface:

interface CustomErrorInterface extends Error {
  customProperty: string;
}

Code Examples

Try-Catch Example

Here's an example of how to use a try-catch statement:

try {
  throw new Error("An error occurred");
} catch (error) {
  console.error(error.message); // "An error occurred"
}

Custom Error Class Example

Here's an example of how to define and use a custom error class:

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

try {
  throw new CustomError("A custom error occurred");
} catch (error) {
  if (error instanceof CustomError) {
    console.error(error.message); // "A custom error occurred"
  }
}

Error Interface Example

Here's an example of how to define an error interface and use it:

interface CustomErrorInterface extends Error {
  customProperty: string;
}

let error: CustomErrorInterface = {
  name: "CustomError",
  message: "A custom error occurred",
  customProperty: "some value",
};

console.error(error.customProperty); // "some value"

Summary

In this tutorial, you learned how to handle errors in TypeScript using the try-catch statement. You also learned how to create custom error classes and define error interfaces.

As next steps, you could explore more about Promise rejection handling and async/await error handling in TypeScript. The TypeScript Handbook is a great resource for learning more about TypeScript.

Practice Exercises

1. Create a try-catch statement that throws and catches an Error with your own custom message.
2. Define a custom error class that extends Error, and use it in a try-catch statement.
3. Define an error interface with a custom property, create an object that adheres to the interface, and log the custom property.

Solutions:

1. Solution:
   typescript try { throw new Error("My custom error message"); } catch (error) { console.error(error.message); // "My custom error message" }
2. Solution:
   ```typescript
   class MyCustomError extends Error {
   constructor(message?: string) {
   super(message);
   this.name = "MyCustomError";
   }
   }

try {
throw new MyCustomError("My custom error occurred");
} catch (error) {
if (error instanceof MyCustomError) {
console.error(error.message); // "My custom error occurred"
}
}
3. Solution:typescript
interface MyCustomErrorInterface extends Error {
myCustomProperty: string;
}

let error: MyCustomErrorInterface = {
name: "MyCustomError",
message: "My custom error occurred",
myCustomProperty: "my custom value",
};

console.error(error.myCustomProperty); // "my custom value"
```

Tips for further practice: Try to use these error handling techniques in a real TypeScript project.