Use variable declared as const as literal type

It would be nice to be able to use a variable declared as const as a literal type in a type annotation.

TypeScript Version: 2.0.0

Code

export const INCREMENT = 'INCREMENT';
export const DECREMENT = 'DECREMENT'
export const ADD = 'ADD';

type Action =
      { type: INCREMENT }
    | { type: DECREMENT };

Expected behavior:
No error, type Action is { type: 'INCREMENT' } | { type: 'DECREMENT' }.

Actual behavior:
Error: Cannot find name INCREMENT

Ok,

export const INCREMENT : 'INCREMENT' = 'INCREMENT';
export const DECREMENT : 'DECREMENT' = 'DECREMENT';

type Action =
      { type: typeof INCREMENT }
    | { type: typeof DECREMENT };

seems to work, but why is const INCREMENT = 'INCREMENT'; of type string and not of type INCREMENT?

This is fixed in 2.1 by #10676.

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Use variable declared as `const` as literal type #12603

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Use variable declared as const as literal type #12603

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Lenne231 commented on Dec 1, 2016

ahejlsberg commented on Dec 1, 2016

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Use variable declared as `const` as literal type #12603