---
title: "Discussion on \"The right way to create utility functions in TypeScript\" | Hashnode"
description: "Discussion on \"The right way to create utility functions in TypeScript\". Utility functions are part of every project.\nYou might organize them in folders called helper, lib, or shared, but their function is the same:\nThey make sure your business logic stays consistent in your game.\n(Drop a like if you love the rhyme. 🤫🎤�..."
url: "https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818"
---

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# [The right way to create utility functions in TypeScript](https://akoskm.com/the-right-way-to-create-utility-functions-in-typescript?utm_source=hashnode&utm_medium=feed)

Utility functions are part of every project. You might organize them in folders called helper, lib, or shared, but their function is the same: They make sure your business logic stays consistent in your game. (Drop a like if you love the rhyme. 🤫🎤�...

Jan 5, 2024 · 3 min read · akoskm.com  
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-   [#typescript](https://hashnode.com/tag/typescript)
-   [#web-development](https://hashnode.com/tag/web-development)
-   [#beginners](https://hashnode.com/tag/beginners)
-   [#design-and-architecture](https://hashnode.com/tag/design-and-architecture)
-   [#javascript](https://hashnode.com/tag/javascript)

## Written by

[Ákos Kőműves](https://hashnode.com/@akoskm)

@akoskm

  
[View profile](https://hashnode.com/@akoskm)

Full-Stack Developer and Writer

I build web apps and make educational content to help web developers.

## Responses 3

Markdown supported · ⌘↵ to post

[Gabby Katherine](https://hashnode.com/@GabbyKather)

[Aug 17, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/66c0f5a1a3db1be9b505d36b)

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[Aug 17, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/66bfedf25852b482995623d9)

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[Aug 13, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/66baee07bc530e1bd4143ce9)

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[Aug 9, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/66b64c33a5a2b561e5d516a2)

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[Tải Go88](https://hashnode.com/@taigo88lat24)

[Aug 8, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/66b4362d77ef9e88dc2b6942)

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[Furkan Emin Can](https://hashnode.com/@femincan)

[Jan 6, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/65998e705a246ab4fe8981ea)

Thanks for the great article [Ákos Kőműves](https://hashnode.com/@akoskm).

I've played with your example and converted it to a type predicate function.

The `isCollaboratorExternal` function accepts a `collaborator` parameter with type `string` and uses the `Array.some` function (because of [this issue](https://github.com/Microsoft/TypeScript/issues/26255)) to check if `externalCollaboratorTypes` has the `collaboratorType` and returns the type predicate.

Thus, after the check operation the type of `data.collaborator.type` will be `"External Editor" | "External Administrator"`.

I think types are more aligned with the logic in this solution.

Here is the link for TypeScript Playground: [TS Playground](https://www.typescriptlang.org/play?#code/MYewdgzgLgBAJgQygmBeGBvAUDGoA2+CARiAE5LkBcmOuMUAngA4CmNA5AOoCWAXgjJwOdAL5ZRAbixZQkWAGEA8gBkVAQQBCSgErqAKroD6+gJoAFAKIBlNLVwAiSwBEAkoZ0OaTgB5RWZGAI+DCWcDxQ5A4ANHQO6s4Asq4Acq7W+noeXjC+-oHBMOpwALY8YDzQFJFkMXEA4gCqNvo5DvUArqzQdY5K+gASljpGympauga6bUpQABYBMAoghCTklLUSMAgQeODQ0rL7sKx+AUH4y6uk1eT6LN12ANp0YxraWcZmVtYAdC7uXSxXBvCafEbfGy-BLJNIZcGxAC6hwAZh0wMAoDxwDBKlciDcNpYzgV8AAKAgE9Y1e5sGhVcoAcwAlDRKWtbmRaaxcbsmGwQCiYKd8hd8RyNtyIE8wB0SsQAoj7DAyKwoB1AsKSWKVlTOVLfhAQCVWGSRedguLCTSHmgAHxa0WW3USm1sNCodDs613B7M6TiI7yPbXam+93oRDIX7esNkX781jSAD0yfoMAAegB+GQ8IVkvEun1kYlO8lRhAxotxhN+5nKuTQEN6yW2yNISuxzm1th0VPp7MSIA)

[Ákos Kőműves](https://hashnode.com/@akoskm)

[Jan 6, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/65998e705a246ab4fe8981ea#reply-6599b86d5a246ab4fe8b00da)

This is interesting. Thanks for sharing it! What would be the advantage of using this over includes and returning a boolean?

[Furkan Emin Can](https://hashnode.com/@femincan)

[Jan 7, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/65998e705a246ab4fe8981ea#reply-659a541a5a246ab4fe8ed97a)

For the first part of your question, the reason why I didn't use `Array.includes` is because of a problem with TypeScript.

As far as I understand, TypeScript doesn't allow us to use a more generic typed search parameter for a more explicitly typed array in the `Array.includes`. So we can't use the type `string` with an array typed `("External Editor" | "External Administrator")[]`.

As a workaround we can set the parameter type `as any`, but I thought `Array.some` is more straightforward to work with (we don't need to disable type checking), and also I couldn't find any performance difference between the two.

For the second part of the question, returning a `boolean` doesn't give us any type narrowing.

If you use the function with an if statement, inside the statement, the type of `data.collaborator.type` is still `string`.

On the contrary, returning type predicate gives us type narrowing.

If we call this function with an `if` statement, inside the statement, the type of `data.collaborator.type` is narrowed to `"External Editor" | "External Administrator"`.

There is a visualization in the [TS Playground](https://www.typescriptlang.org/play?#code/MYewdgzgLgBAJgQygmBeGBvAUDGoA2+CARiAE5LkBcmOuMUAngA4CmNA5AOoCWAXgjJwOdAL5ZRAbixZQkWAGEA8gBkVAQQBCSgErqAKroD6+gJoAFAKIBlNLVwAiSwBEAkoZ0OaTgB5RWZGAI+DCWcDxQ5A4ANHQO6s4Asq4Acq7W+noeXjC+-oHBMOpwALY8YDzQFJFkMXEA4gCqNvo5DvUArqzQdY5K+gASljpGympauga6bUpQABYBMAoghCTklLUSMAgQeODQ0rL7sKx+AUH4y6uk1eT6LN12ANp0YxraWcZmVtYAdC7uXSxXBvCafEbfGy-BLJNIZcGxAC6hwAZh0wMAoDxwDBKlciDcNpYzgV8AAKAgE9Y1e5sGhVcoAcwAlDRKWtbmRaaxcbsmGwQCiYKd8hd8RyNtyIE8wB0SsQAoj7DAyKwoB1AsKSWKVlTOVLfhAQCVWGSRedguLCTSHmgAHxa0WW3USm1sNCodDs613B7M6TiI7yPbXam+93oRDIX7esNkX781jSAD0yfoMAAegB+GQ8IVkvEun1kYlO8lRhAxotxhN+5nKuTQEN6yW2yNISuxzm1th0VPp7MSIA) that shows the result of narrowing the type.

As I said, I think this approach is more suitable for the TypeScript side, for the JavaScript side there is nearly no difference.

[Ákos Kőműves](https://hashnode.com/@akoskm)

[Jan 8, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/65998e705a246ab4fe8981ea#reply-659bc69eb80581bc1952d343)

Thanks for the explanation [Furkan Emin Can](https://hashnode.com/@femincan).

I looked at your example once more, and I think it does more (which completely justifies the different typing) compared to my simple example. Yours returns the actual collaborator type if the supplied `data.collaborator.type` matches a collaborator type.

In my example, I simply want to know if the value of `data.collaborator.type` is an external collaborator. Since it's either yes or no, `boolean` gives sufficient type narrowing (true/false).

[Md Taqui imam](https://hashnode.com/@taqui786)

[Jan 6, 2024](https://hashnode.com/posts/the-right-way-to-create-utility-functions-in-typescript/659812adc22d321fff4af818/comment/65994dbd0fe390a9f91a526a)

🔥🔥🔥