consistent-indexed-object-style.md

Pattern: Mixed indexed object type syntax

Issue: -

Description

TypeScript provides multiple ways to define objects with arbitrary keys: index signatures ([key: string]: T), mapped types ([K in string]: T), and the Record utility type. Using different styles within the same codebase reduces readability and creates inconsistent patterns.

Examples

Example of incorrect code when preferring Record:

// Using index signature
interface StringMap {
  [key: string]: unknown;
}

// Using type with index signature
type NumberMap = {
  [key: number]: string;
};

// Using mapped type
type BooleanMap = {
  [K in string]: boolean;
};

Example of correct code when preferring Record:

// Using Record consistently
type StringMap = Record<string, unknown>;
type NumberMap = Record<number, string>;
type BooleanMap = Record<string, boolean>;

Example of incorrect code when preferring index signature:

// Using Record type
type StringMap = Record<string, unknown>;
type NumberMap = Record<number, string>;

Example of correct code when preferring index signature:

// Using index signature consistently
interface StringMap {
  [key: string]: unknown;
}

type NumberMap = {
  [key: number]: string;
};

interface DataMap {
  [key: string]: number;
}