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What are global types in TypeScript and how to use them?

TypeScript has proven to be a powerful tool for developers, allowing the definition of types that improve code quality and aid in error prevention. An essential aspect of TypeScript is the option to define global types that can be used in all files in an application, known as global types. Although they are extremely useful, it is important to handle them with care and to understand when and how to implement them properly.

What are global types?

Global types in TypeScript allow certain type definitions to be accessible from any file in the application. They are usually defined in files with a .d.ts extension, known as declaration files. These files describe the general types of an application and their correct implementation is essential to maintain consistency and avoid problems in the code.

How to create global types?

To create a global type in TypeScript, you need to follow a series of steps:

1. Declaration file: Global types must be defined inside a file with extension .d.ts. For example, app.d.ts is a common name used to store global types.

2. Type definition: Any type definition that should be global should be moved from its local ubiquity to this declaration file. For example, if you have an ImageItem type that consists of an ID and a URL, you can move it from the local component to the app.d.ts file.

3. Type naming: It is recommended to follow a naming convention where global types start with a capital letter I or T to indicate that it is a global type. For example: IImageItem.

4. Project configuration: It is vital to ensure that the tsconfig.json file is configured to include all .ts files, ensuring that TypeScript processes the global types file correctly.

Best practices for using global types.

Implementing global types should be done with caution. Here are some tips:

• Global relevance: define a type as global only if it is truly relevant to the entire application. Avoid falling into the trap of making all types global, as this can cause confusion and disorganization in the project.

• Keep local first: Start by defining types locally within specific components. Evaluate making them global only when they need to be used in multiple files in the application. Also, it is good practice to consult with the team before making this decision.

• Good documentation: Make sure that each global type is well documented to facilitate its understanding and correct use by other team members.

Practical example of TypeScript code

Here is an example of how to properly organize a global type in an app.d.ts file:

// app.d.ts
interface IImageItem { id: string; url: string;}

This IImageItem type is now available for use anywhere in the application, improving consistency and reducing the possibility of type-related errors.

Final Tips

Global types are powerful and, if used correctly, can significantly improve the efficiency of TypeScript development. However, they should be used with discernment and always with an eye toward maintaining project structure and organization. Be sure to follow established conventions and maintain open communication with your team to maximize the benefits that global types offer. Continue to explore and learn about the capabilities of TypeScript and how it can enhance your projects.