isolatedDeclarations: Inconsistent type requirement for as const when using satisfies #62476

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1. MartinJohns commented on Sep 22, 2025

   

   Martin Johns (MartinJohns)

   on Sep 22, 2025

   Contributor

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   Duplicate of #58397.

   👍React with 👍1Reacted by Christopher J. Tannum
2. Christopher J. Tannum (christjt)

   closed this as a duplicateof [isolatedDeclarations][5.5] Adding satisfies to a const expression makes it require explicit type annotation #58397 on Sep 23, 2025
3. barryam3 commented on Nov 21, 2025

   

   Barry A. McNamara III (barryam3)

   on Nov 21, 2025

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   Since #58397 is locked I am replying here.

   If the satisfies operator doesn't change the type of the inferred expression, then it's always safe to rewrite this into two lines:

   export const foo = {
    a: 42
   } as const;
   foo satisfies Record<string, number>;

   ― Ryan Cavanaugh (@RyanCavanaugh)

   While visually will take some getting used to, I suppose that's a good enough solution (thank you for taking the time to think > of and provide one and not just mansplaining how things work).

   ― michaelm (@MichaelMitchell-at)

   Unfortunately this isn't quite as good if you want to ensure that the type doesn't contain any extraneous fields. Here's an example:

   export const foo = {  // Variable must have an explicit type annotation with --isolatedDeclarations.(9010)
       a: { a: 42 },
       b: { a: 42, b: 42 },  // Object literal may only specify known properties, and 'b' does not exist in type '{ a: number; }'.(2353)
       c: {}  // Property 'a' is missing in type '{}' but required in type '{ a: number; }'.(2741)
   } as const satisfies Record<string, { a: number }>;
   
   export const bar = {
       a: { a: 42 },
       b: { a: 42, b: 42 },  // Allowed
       c: {}  // Error, but not inline
   } as const;
   bar satisfies Record<string, { a: number }> /*
   Type '{ readonly a: { readonly a: 42; }; readonly b: { readonly a: 42; readonly b: 42; }; readonly c: {}; }' does not satisfy the expected type 'Record<string, { a: number; }>'.
     Property 'c' is incompatible with index signature.
       Property 'a' is missing in type '{}' but required in type '{ a: number; }'.(1360)
   */

   The as const satisfies version works as I would prefer except that it gives an error with --isolatedDeclarations.

   The delayed satisfies workaround has a couple of limitations:

   • It doesn't enforce that unknown properties are not present.
   • If a field does not satisfy the type, the error is deferred until the satisfies clause and contains much more text, whereas in the as const satisfies case it appears inline and is more succinct.
4. microsoft

   locked as resolved and limited conversation to collaborators on Jan 20, 2026