How to Create a Type with Keys from a Union Type and Different Value Types in TypeScript

Learn how to define types in TypeScript that combine union types and distinct object types, ensuring type safety and preventing errors.
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How to Create a Type with Keys from a Union Type and Different Value Types in TypeScript

When working with TypeScript, you might find yourself needing to create a type that uses keys from a union type while also defining distinct value types for each key. This can be particularly useful in scenarios where you want to ensure that you can only use a limited set of keys associated with specific object shapes. Below, we will explore how to achieve this effectively while maintaining type safety.

Understanding the Problem

Let’s say you have a union type that consists of two identifiers, item1 and item2, and you have defined specific types for each of these identifiers. The goal is to create a new type called MyRecord where the keys are restricted to the values of the union type, and the values correspond to the respective types.

Your Union Type

Initially, you’ve defined your union type as follows:

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Item Types

You also have different item types defined like this:

[[See Video to Reveal this Text or Code Snippet]]

Expected Structure

You would like your MyRecord type to have this structure:

[[See Video to Reveal this Text or Code Snippet]]

However, you want TypeScript to enforce the validity of the keys so that if you mistakenly use an undefined key like item3, you will get a compile-time error.

The Solution

To implement this, you can leverage TypeScript's powerful utility types and mapping capabilities. There are a couple of approaches you can take to create the desired MyRecord type while maintaining key safety.

Approach 1: Using Record Utility Type

One straightforward approach is to utilize TypeScript’s built-in Record utility type. This utility allows you to create an object type with specific keys and value types. Here is how you can do it:

[[See Video to Reveal this Text or Code Snippet]]

Approach 2: Using Intersection Types

Alternatively, you can define individual types for each item and then create an intersection type to combine them. This method allows you to explicitly define what each key holds without losing type integrity.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following the approaches outlined above, you can effectively create a type in TypeScript that combines keys from a union type and assigns different object types to each key. This not only helps in organizing your code but also enhances type safety by catching potential errors at compile-time.

Whether you choose to use the Record utility or intersection types, TypeScript offers the flexibility needed to ensure that your data structures are both robust and clear. Embrace the power of TypeScript to create types that work best for your specific use cases!