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official_dulin
official_dulin

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Use TypeScript interface extends and type composition semantically

#typescript #discuss

Consider below example, you have an API which accepts three parameters: current, pageSize and channelCode.

interface Pagination { current: number; pageSize: number; } interface GetUsersByPageRequestDTO { channelCode?: string; }
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Now you have two choice to pack these parameters.

Option 1:

interface GetUsersByPageRequestDTO extends Pagination { channelCode?: string; }
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Option 2:

type GetUsersByPageRequestDTO = { channelCode?: string; } & Pagination;
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Which one will you choose? Inheritance or composition?

For me, I will choose option 2, use intersection type(type composition). Because using inheritance requires semantic correctness. Which means the two need to have is-a relationship. E.g. Bear is an animal. So bear interface can extend animal interface.

Apparently, GetUsersByPageRequestDTO is NOT a Pagination.

So we know the difference between interface and type, but we also have to pay attention to the semantic correctness, not only to get the final correct shape, right?

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