Understanding When to Use Maybe Type Over Question Mark in TypeScript

Описание: Discover the advantages of using `Maybe` type versus the question mark in TypeScript when defining optional properties in your classes.
---
This video is based on the question https://stackoverflow.com/q/67313439/ asked by the user 'Serhii Shliakhov' ( https://stackoverflow.com/u/1600992/ ) and on the answer https://stackoverflow.com/a/67314567/ provided by the user 'Maciej Sikora' ( https://stackoverflow.com/u/4420812/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Why I should prefer either Maybe type over question mark or vise versa?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
When Should You Prefer Maybe Type Over Question Mark in TypeScript?

In TypeScript, defining optional class properties is a common task. You might have encountered two prominent methods: using a question mark (?) after the property name or utilizing a Maybe type. This raises an important question: Should you prefer one over the other? Let's explore the differences and implications of each approach.

The Basics: Optional Properties in TypeScript

When defining a class, you may want a property to be optional. Here are two ways to do it:

Using a Question Mark:

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

Using Maybe Type:

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

At first glance, both approaches seem similar, but they serve different purposes and have distinct implications in your code.

Understanding the Difference

1. Optional Field Using Question Mark (mouth?)

Using mouth? allows you to omit the property entirely when you're creating an instance of the class. For instance:

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

Key Feature: You can create an object of type Animal without defining the mouth property, which makes it very flexible.

2. Explicit undefined with Maybe Type (mouth: Maybe<Mouth>)

On the other hand, if you define mouth using the Maybe type, you're enforcing an explicit structure:

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

Key Feature: This forces the property to either be a valid object of the type or explicitly undefined. However, it won't allow you to omit the property altogether.

An In-depth Comparison

The main difference lies in how these two approaches handle property assignment:

With maybe?:

The property can be omitted completely, allowing for a wider definition of possible values.

This is useful in cases where the absence of a property might be semantically significant.

With Maybe<T>:

The property must exist but can explicitly be set to undefined, making this less flexible.

It may be appropriate in scenarios where the property is intended to signify a specific state, like indicating that it was cleared in a PATCH request.

Summary of When to Use Each

Prefer mouth?:

When you want easier object creation with optional fields.

Use it when the absence of a value is a valid or common situation.

Use Maybe<Mouth>:

When you need to explicitly mark a property that may be left undefined but still intended to be present.

It's beneficial when you have particular logic to manage properties that might be "cleared" or absent using operations over keys.

Additional Insight: The Disjoint Union Concept

It's worth noting that the Maybe type is a form of disjoint union rather than a simple union. A more detailed definition would look like this:

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

This offers a more expressive way to handle presence and absence of values, separate from nullable types.

Conclusion: Making the Right Choice

In choosing between Maybe type and the question mark, it's essential to consider the context in which you're working. While mouth? generally provides more flexibility in your code, Maybe type can be crucial in specific scenarios that require explicit handling of undefined values.

Making informed decisions based on your requirements will help you write cleaner, more understandable TypeScript code.

By taking the time to understand these differences, you can ensure your class properties align with the intended behavior of your application.