Want to improve your Typescript skills? Check out our guide covering basics, built-in types, custom errors, and tools.
Typescript Error Handling Basics
When developing software applications, it’s inevitable to encounter errors at some point. These errors can be caused by different factors such as coding mistakes, incorrect input values, or unexpected system crashes. Therefore, it’s important to have a robust error handling mechanism in place to ensure that the application can handle errors gracefully and avoid crashing.
In Typescript, is done through the use of try-catch blocks. A try-catch block allows you to execute a block of code and catch any errors that may occur. The syntax for a try-catch block is as follows:
try {
// code that may throw an error
}
catch(error) {
// code to handle the error
}The try block contains the code that may throw an error, and the catch block is used to handle the error. If an error occurs in the try block, the catch block will be executed, and the error object will be passed as an argument.
Try-Catch Block Syntax
Let’s take a closer look at the syntax of a try-catch block. The try block contains the code that may throw an error. This can be any block of code, such as a function or a loop. If an error occurs in the try block, the catch block will be executed. The catch block takes an error object as an argument, which contains information about the error that occurred.
Here’s an example of how to use a try-catch block:
try {
let result = performCalculation(10, 0);
console.log(result);
}
catch(error) {
console.error(error.message);
}In this example, the performCalculation function may throw an error if the second argument is zero. If an error occurs, the catch block will be executed, and the error message will be logged to the console.
Throwing Custom Errors
Sometimes, you may want to throw a custom error in your code to provide more information about what went wrong. Typescript allows you to create custom error types by extending the built-in Error class.
Here’s an example of how to create a custom error type:
class CustomError extends Error {
constructor(message: string) {
super(message);
this.name = "CustomError";
}
}In this example, we create a new class called CustomError that extends the built-in Error class. We set the name of the error to “CustomError” and pass the error message to the constructor.
To throw a custom error, you can use the throw keyword followed by an instance of the custom error class:
throw new CustomError("Something went wrong");Handling Async Errors
When working with asynchronous code, error handling can become more complicated. Asynchronous code is code that doesn’t execute in a linear fashion, but instead executes in parallel with other parts of the code. This means that errors can occur in different parts of the code, and it can be difficult to track them down.
To handle asynchronous errors in Typescript, you can use the try-catch block in combination with Promises. Promises are a way to handle asynchronous code in a more structured way.
Here’s an example of how to handle errors in an asynchronous function using Promises:
async function performAsyncTask() {
try {
let result = await fetch("https://example.com");
console.log(result);
}
catch(error) {
console.error(error.message);
}
}In this example, the performAsyncTask function uses the await keyword to wait for the fetch function to complete before continuing. If an error occurs, the catch block will be executed, and the error message will be logged to the console.
By using Promises and the try-catch block, you can handle asynchronous errors in a more structured and predictable way.
Overall, Typescript provides a robust mechanism that allows you to handle errors gracefully and avoid application crashes. By using try-catch blocks, custom error types, and Promises, you can create a more structured and predictable error handling system in your Typescript code.
Using Typescript’s Built-in Error Types
Typescript is a programming language that is widely used in web development. In Typescript, errors can occur when there is a syntax error, a logical error, or when there is an issue with the code execution. To help developers identify and resolve these errors, Typescript has built-in error types that can be used to catch and handle errors.
Error
The Error class is the most basic error type in Typescript. It represents a generic error that can occur during the execution of code. When an error occurs, an error object is created, which contains information about the error, including the error message, the stack trace, and any other relevant information.
To use the Error class, you can create a new instance of the class and pass in a message that describes the error. For example:
typescript
try {
// some code that may throw an error
} catch (error) {
const errorMessage = error.message;
console.error(errorMessage);
}In the code above, we use a try-catch block to catch any errors that may occur. If an error does occur, we create a new instance of the Error class and pass in the error message. We then log the error message to the console.
TypeError
The TypeError class is a specific type of error that occurs when a value is not of the expected type. For example, if you try to call a method on a null or undefined value, you will get a TypeError.
To handle TypeError in Typescript, you can create a new instance of the TypeError class and pass in an error message. For example:
typescript
try {
const num: number = null;
console.log(num.toFixed(2));
} catch (error) {
if (error instanceof TypeError) {
console.error("Value is not a number");
}
}In the code above, we try to call the toFixed() method on a null value, which will result in a TypeError. We then catch the error and check if it is an instance of the TypeError class. If it is, we log an error message to the console.
RangeError
The RangeError class is another specific type of error that occurs when a value is out of range. For example, if you try to call the slice() method on a string with a start or end index that is out of range, you will get a RangeError.
To handle RangeError in Typescript, you can create a new instance of the RangeError class and pass in an error message. For example:
typescript
try {
const str: string = "hello";
console.log(str.slice(0, 10));
} catch (error) {
if (error instanceof RangeError) {
console.error("Index out of range");
}
}In the code above, we try to call the slice() method on a string with a start index of 0 and an end index of 10, which is out of range. We then catch the error and check if it is an instance of the RangeError class. If it is, we log an error message to the console.
Creating Custom Error Types
When it comes to in Typescript, it’s not always enough to rely on the built-in error types. Sometimes, you need to create your own custom error types to better handle specific situations.
Extending the Error Class
To create a custom error type, you can extend the built-in Error class in Typescript. This allows you to add your own properties and methods to the error object. Here’s an example:
typescript
class CustomError extends Error {
constructor(message: string, public readonly errorCode: number) {
super(message);
}
}In this example, we’re creating a custom error class called CustomError that extends the Error class. We’ve also added a new property called errorCode, which is a number that represents the specific error code for this error type.
Adding Custom Properties to Error Objects
Adding custom properties to error objects can be useful for providing additional context about the error. For example, you might want to include a timestamp or a user ID to help you track down the source of the error. Here’s how you can do it:
typescript
const error = new CustomError('Something went wrong', 500);
error.timestamp = new Date();
error.userId = '123456';In this example, we’ve created a new instance of our custom error type and added two custom properties: timestamp and userId. These properties can now be accessed anywhere that the error object is passed around in your code.
Creating a Custom Error Handler
To handle custom error types, you’ll need to create a custom error handler. This handler should be able to recognize your custom error type and take appropriate action based on the error code and any custom properties that have been added.
Here’s an example of how you might create a custom error handler for our CustomError type:
typescript
function handleError(error: Error) {
if (error instanceof CustomError) {
// Handle the custom error type
console.log(`Custom error with code ${error.errorCode}: ${error.message}`);
console.log(`Timestamp: ${error.timestamp}`);
console.log(`User ID: ${error.userId}`);
} else {
// Handle other error types
console.log(`Error: ${error.message}`);
}
}In this example, we’ve created a function called handleError that takes an error object as its parameter. We’ve then used the instanceof operator to check if the error is an instance of our CustomError class. If it is, we log some additional information about the error, including the error code, timestamp, and user ID. If it’s not a CustomError, we handle it as a generic error.
By creating custom error types and error handlers in Typescript, you can provide more meaningful error messages and better handle specific error scenarios in your code.
Debugging Typescript Errors
Debugging errors in Typescript can be a challenging task, but with the right tools and techniques, it can become more manageable. In this section, we will explore some of the essential methods and tools developers can use to debug Typescript errors.
Using Debugging Tools
One of the most effective ways to debug Typescript errors is to use tools. These tools allow developers to step through their code, set breakpoints, and inspect variables. Some of the popular tools for Typescript include:
- Chrome DevTools: This is a web developer tool built into the Chrome browser that enables developers to debug JavaScript and Typescript code. It provides a comprehensive suite of tools, including a console for logging messages, breakpoints, and a debugger for stepping through code.
- Visual Studio Code Debugger: This is a powerful tool built into the Visual Studio Code editor that enables developers to debug Typescript code directly from within the editor. It provides features such as breakpoints, step into/over/out of code, and a variable inspector.
- Node.js Debugger: This is a command-line tool that allows developers to debug Typescript code running on Node.js. It provides features such as breakpoints, stepping through code, and variable inspection.
Using these tools, developers can gain deeper insights into their code and find and fix errors more quickly.
Debugging with Visual Studio Code
Visual Studio Code is an excellent IDE for developing Typescript applications. It provides a range of built-in tools that make it easy to debug Typescript code. Here are some steps to follow when with Visual Studio Code:
- Set a breakpoint: In the editor, click on the line number where you want to set a breakpoint. A red dot will appear, indicating that a breakpoint has been set.
- Start : Click the “Run” button in the toolbar, or press F5 to start .
- Debugging session: The session will start, and the code will stop at the breakpoint. You can step through the code, inspect variables, and use the console to log messages.
- Fix errors: Once you have identified the error, make the necessary changes to fix it, save the file, and continue .
Common Typescript Error Messages
Typescript provides detailed error messages that can help developers identify and fix errors in their code. Here are some of the common Typescript error messages and their meanings:
- “Cannot find module”: This error occurs when Typescript cannot find a module that you are trying to import. The solution is to ensure that the module is installed and correctly referenced in your code.
- “Property does not exist on type”: This error occurs when you are trying to access a property that does not exist on the type you are working with. The solution is to check that the property exists on the type or to use a type assertion.
- “Type ‘x’ is not assignable to type ‘y'”: This error occurs when you are trying to assign a value of the wrong type to a variable. The solution is to ensure that the value you are assigning is of the correct type.
In conclusion, Typescript errors can be a challenging task, but with the right tools and techniques, it can become more manageable. By using tools, such as Chrome DevTools, Visual Studio Code Debugger, and Node.js Debugger, developers can gain deeper insights into their code and find and fix errors more quickly. Additionally, Typescript provides detailed error messages that can help developers identify and fix errors in their code.
