Скачать или смотреть How to Use Typescript Union Type for Each Property of Another Type

Discover an efficient way to automate the creation of TypeScript union types for class properties instead of manually defining them.
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This video is based on the question https://stackoverflow.com/q/64703588/ asked by the user 'psteinroe' ( https://stackoverflow.com/u/6570537/ ) and on the answer https://stackoverflow.com/a/64704098/ provided by the user 'captain-yossarian from Ukraine' ( https://stackoverflow.com/u/8495254/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Simplifying TypeScript Union Types for Class Properties

TypeScript is a powerful tool for developers, enabling them to define types for variables, function parameters, and return values. However, when it comes to creating union types from existing class properties, it can become tedious if done manually. This guide addresses a common situation encountered by many TypeScript developers—automating the process of creating union types for class properties.

The Challenge

Let's consider a class definition that many developers may be familiar with:

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In this example, we have a User class with multiple properties, some of which are optional. The problem arises when you want to create another type that includes a few selected properties but with a union type that includes FieldValue for each one, like this:

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Manually defining the union types for each property can be a hassle and can lead to errors. This raises the question: Is there a more efficient way to automate this process?

The Solution

The answer is yes! TypeScript allows us to create a helper type that can automate the generation of union types for our properties. In this section, we’ll outline the steps needed to achieve this.

Step 1: Define FieldValue

Firstly, you need to define what FieldValue looks like. In this case, it could be a simple type that holds some properties, like so:

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Step 2: Create the Initial Type

Next, we create the initial type that consists of the properties we want to work with.

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Step 3: Develop the Unionization Helper Type

Here’s the magic! We create a helper type called Unionize that applies the union type for each property defined in our initial type.

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Step 4: Create Your Final Type

Now that we have this helper, we can easily create our final type without writing out the union for each property manually.

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Summary

By utilizing a combination of generics and mapped types, we can dramatically simplify the task of creating union types for each property of another type. This technique not only saves time but also reduces the likelihood of introducing errors in your TypeScript code.

Conclusion

In this post, we’ve explored how to efficiently create TypeScript union types for the properties of a predefined class using a helper type. Embrace the power of TypeScript and simplify your coding process by implementing these techniques in your own projects. Happy coding!