A Complete Guide to Using Optional Parameters in TypeScript Functions with ResizeOptions

Discover how to effectively manage optional parameters in TypeScript functions, ensuring compliance with coding standards and avoiding common pitfalls in handling default values.
---

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: Third parameter in a function is an optional object with default values. How to write it to make typescript happy?

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
A Complete Guide to Using Optional Parameters in TypeScript Functions with ResizeOptions

When developing applications in TypeScript, you may often encounter the need to provide optional parameters to functions. This can be particularly useful when you want to allow users to specify only the values they desire while providing sensible defaults for other parameters. In this guide, we’ll explore a common problem related to optional parameters and how to implement a solution that will keep TypeScript happy.

The Problem: Using Optional Parameters in a Function

Let’s consider a function responsible for resizing an image. Here’s the function signature we are dealing with:

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

In this function, the third parameter is an optional object containing default values for width and height. However, when you call this function without specifying the third argument, TypeScript throws an error:

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

You want to be able to call the function with just two parameters and use the predefined default values for the optional object.

The Solution: Modifying the Function to Handle Optional Parameters

To gracefully handle this situation while keeping both TypeScript and ESLint happy, you can leverage default values properly in your function’s signature. Below are the steps to implement this solution.

Step 1: Create an Interface for the Options

Define an interface to declare the shape of the options you plan to use:

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

Step 2: Modify the Function to Accept an Optional Object

Update the resizeImage function to accept an optional ResizeOptions parameter, implementing default values directly in the function signature:

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

Step 3: Handle Default Value Assignment

By defining resizeOptions with a default object, you ensure that even if the caller doesn’t specify the third parameter, your function will still have default values for width and height.

Summary of the Code

Putting it all together, your modified function will look like this:

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

Important Considerations

Avoid Mutating Defaults: By providing the default object directly in the function parameters, you avoid the risk of using an object literal as a default which might lead to unpredictable behaviors in your code base when optional parameters are passed.

Type Safety: The use of an interface ensures that TypeScript understands the expected structure of the resize options, helping catch errors during development.

Conclusion

Incorporating optional parameters into your TypeScript functions can improve flexibility and usability, but it can also introduce complexity. By following these guidelines and using the right patterns, you can avoid common pitfalls and maintain clean, functional code. Now, you can confidently implement optional parameters in your TypeScript projects!

Feel free to try this approach and watch TypeScript give you the thumbs up while also keeping your code error-free.