👀 Views: 86 💬 Answers: 1 📅 Created: 2025-09-06

TypeScript Type Guards Custom Types tutorial

I'm refactoring my project and After trying multiple solutions online, I still can't figure this out... # Learning Objectives In this guide, you will learn how to implement custom type guards in TypeScript. By the end of this tutorial, you will be able to enhance type safety in your applications and make your TypeScript code more robust and maintainable. ### What You Will Achieve - Understand the concept of type guards in TypeScript. - Implement custom type guards to refine types at runtime. - Utilize type guards in real-world scenarios to improve code quality. ## What Are Type Guards? Type guards are a TypeScript feature that allows you to define and narrow down types based on runtime checks. By using type guards, you can ensure that your variables are of the expected type before performing operations on them. ## Implementing Custom Type Guards Custom type guards are functions that return a boolean value indicating whether a variable is of a specific type. Here’s how to create one: ### Step 1: Define Your Types First, define the types you will be working with. For instance, we can create an interface for a `User`: ```typescript interface User { name: string; age: number; } interface Admin extends User { privileges: string[]; } interface Guest extends User { accessLevel: number; } ``` ### Step 2: Create the Type Guard Function Now, let's create a custom type guard function that checks if a user is an `Admin`: ```typescript function isAdmin(user: User): user is Admin { return (user as Admin).privileges !== undefined; } ``` ### Step 3: Using the Type Guard You can now use this type guard in your application to check if a user is an `Admin`: ```typescript const user: User = { name: 'Alice', age: 30, privileges: ['manage-users'] }; if (isAdmin(user)) { console.log(`${user.name} is an admin with privileges: ${user.privileges}`); } else { console.log(`${user.name} is a regular user.`); } ``` ### Best Practices - **Always ensure type checks are clear:** Your type guard function should be easy to understand and maintain. - **Use type assertions wisely:** Type assertions can be useful, but they should be used only when necessary to maintain type safety. - **Combine multiple type guards for complex types:** You can create compound type guards that check for multiple conditions, enhancing clarity and type safety in your code. ## Conclusion Custom type guards in TypeScript are a powerful way to enhance type safety and clarity in your applications. By following these steps and best practices, you can develop more robust TypeScript code that is easier to maintain and understand. I'd really appreciate any guidance on this. I'm using Typescript 3.9 in this project. Any advice would be much appreciated. I'm on Linux using the latest version of Typescript. What are your experiences with this?