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javascripttypescripttuples
Shannon Hochkins
Shannon Hochkins

Reputation: 12175

Tuple vs hard coded string

We have this code at our work, which i wanted to know the difference between it and just manually typing out the same thing.

const tuple = <T extends string[]>(...args: T) => args;
const strings = tuple(
  'blabla',
  'default',
  'standard'
);

export type Strings = typeof strings[number];

When i hover over "Strings", it basically is type Strings = 'blabla' | 'default' | 'standard'

My question is, why not just simply type out the samething?

type Strings = 'blabla' | 'default' | 'standard';

Instead of all the tuple stuff? I can't see a difference, but if someone could explain why we're using this Tuple function that would be great

Upvotes: 2

Views: 148

Answers (1)

Oblosys
Oblosys

Reputation: 15106

If you don't export strings then it is definitely better to directly declare the type. In some cases you also need the values though, and using that tuple function saves you from having to specify each one twice.

There's a simpler and safer way to do this though:

export const strings = [ 'blabla', 'default', 'standard' ] as const;
// type: readonly ["blabla", "default", "standard"]

export type Strings = typeof strings[number]
// type Strings = "blabla" | "default" | "standard"

This makes strings readonly, so you can't do an unsound strings.pop() for example.

TypeScript playground

Upvotes: 2

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