TS4104

error TS4104: The type ‘readonly [1, 2, 3]‘ is ‘readonly’ and cannot be assigned to the mutable type ‘[1, 2, 3]‘.

Broken Code ❌

1

const array: [1, 2, 3] = [1, 2, 3] as const;

Fixed Code ✔️

Using a const assertion makes your array immutable, so you have to use the readonly modifier for its type:

1

const array: readonly [1, 2, 3] = [1, 2, 3] as const;

Alternative:

1

const array: Readonly<[1, 2, 3]> = [1, 2, 3] as const;

Alternative #2:

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const array: ReadonlyArray<number> = [1, 2, 3] as const;