TypeScript Mapped Types & Utility Collection

Common errors

• TS2345: Argument of type 'string' is not assignable to parameter of type '{ theme: "dark" | "light"; notifications: boolean; }'.

  cause Attempting to assign a value to a deeply `Readonly` type, which prevents modification of nested properties.
  fix Ensure that if you are using types like `DeepReadonly<T>`, you do not attempt to modify any properties, including nested ones. Create a mutable copy if modification is necessary.

• TypeError: Cannot read properties of undefined (reading 'OmitKeys')

  cause Attempting to use CommonJS `require()` syntax (e.g., `const { OmitKeys } = require('react-redux-typescript');`) in an ES Module context or when the package's `exports` map doesn't permit it.
  fix Use ES Module import syntax: `import { OmitKeys } from 'react-redux-typescript';` Ensure your `tsconfig.json` `module` and `moduleResolution` settings are appropriate for your environment (e.g., 'NodeNext' or 'Bundler').

• TS2344: Type 'string | number' does not satisfy the constraint 'keyof T'.

  cause Using `Omit<T, K>` or `Pick<T, K>` with a key `K` that is not a valid key of type `T`.
  fix Verify that the keys you are attempting to `Omit` or `Pick` (`K`) are indeed present in the base type `T`. TypeScript's strictness prevents operating on non-existent keys, which helps catch typos.

Warnings

• deprecated The 'Redux Typesafe Actions' utilities (e.g., createAction, getType, isActionOf) re-exported from `typesafe-actions` are deprecated and will be removed in the next major release. Users should migrate to importing these directly from `typesafe-actions`.
  Fix: Replace `import { createAction } from 'react-redux-typescript';` with `import { createAction } from 'typesafe-actions';` for affected symbols.
• deprecated The `Falsey` type alias was deprecated in v3.9.0 and replaced with `Falsy`. While `Falsey` is kept for backward compatibility, it is recommended to update to the new alias.
  Fix: Replace `Falsey` with `Falsy` in your type definitions.
• gotcha The package name `react-redux-typescript` is largely historical. Most of its current utility types are general-purpose TypeScript mapped types, with the React/Redux-specific re-exports being deprecated. This can be misleading for new users expecting only React/Redux-specific functionality.
  Fix: Be aware that the primary value of this library lies in its general TypeScript utility types. Consider `utility-types` as a more fitting alternative if not using the specific types offered here, though this library often provides more advanced versions.
• breaking An issue with TypeScript v3.5's native `Omit` implementation caused `react-redux-typescript` to revert to an older, custom `Omit` implementation in v3.6.1 to ensure correctness. While fixed internally, users should be aware of potential subtle differences or unexpected type inference if upgrading from very old versions or encountering edge cases with specific TS versions.
  Fix: Ensure you are using a recent version of `react-redux-typescript` (v3.6.1 or later) to benefit from the corrected `Omit` type. Always test thoroughly when upgrading TypeScript versions in combination with this library.

Install

• npm install react-redux-typescript npm
• yarn add react-redux-typescript yarn
• pnpm add react-redux-typescript pnpm

Imports

• Omit
  wrong:

  import Omit from 'react-redux-typescript';

  correct:

  import { Omit } from 'react-redux-typescript';

  Mapped types are typically imported as named exports. Avoid default imports.
• Assign
  wrong:

  const { Assign } = require('react-redux-typescript');

  correct:

  import { Assign } from 'react-redux-typescript';

  While CommonJS `require` might work in some configurations, named ESM imports are the recommended and type-safe approach for TypeScript.
• getReturnOfExpression
  wrong:

  import * as RRT from 'react-redux-typescript'; const func = RRT.getReturnOfExpression;

  correct:

  import { getReturnOfExpression } from 'react-redux-typescript';

  Destructuring directly from named exports is preferred for tree-shaking and clarity.
• DeepReadonly
  wrong:

  import { Readonly } from 'react-redux-typescript';

  correct:

  import { DeepReadonly } from 'react-redux-typescript';

  Use `DeepReadonly` for recursive readonly application; `Readonly` is a standard TypeScript utility type.

Quickstart

Demonstrates `Omit`, `Assign`, and `DeepReadonly` utility types for manipulating object shapes and immutability.

import { Omit, Assign, DeepReadonly } from 'react-redux-typescript';

interface UserProfile {
  id: string;
  name: string;
  email: string;
  settings: {
    theme: 'dark' | 'light';
    notifications: boolean
  };
  createdAt: Date;
}

interface PartialUpdate {
  name?: string;
  email?: string;
  updatedAt: Date;
}

// Example 1: Omit properties from a type
type UserWithoutSensitiveInfo = Omit<UserProfile, 'email' | 'createdAt'>;
// Expected: { id: string; name: string; settings: { theme: 'dark' | 'light'; notifications: boolean }; }

const user1: UserWithoutSensitiveInfo = {
  id: '123',
  name: 'Alice',
  settings: { theme: 'dark', notifications: true }
};

// Example 2: Assign (merge) properties, overwriting if they exist
type MergedProfile = Assign<UserProfile, PartialUpdate>;
// Expected: { id: string; name: string; email: string; settings: { theme: 'dark' | 'light'; notifications: boolean }; createdAt: Date; updatedAt: Date; }

const user2: MergedProfile = {
  id: '456',
  name: 'Bob',
  email: 'bob@example.com',
  settings: { theme: 'light', notifications: false },
  createdAt: new Date(),
  updatedAt: new Date()
};

// Example 3: Make all properties and nested properties readonly
type ReadonlyUserProfile = DeepReadonly<UserProfile>;

const readonlyUser: ReadonlyUserProfile = {
  id: '789',
  name: 'Charlie',
  email: 'charlie@example.com',
  settings: {
    theme: 'light',
    notifications: true
  },
  createdAt: new Date()
};

// readonlyUser.name = 'David'; // This line would cause a TypeScript error

console.log('User without sensitive info:', user1);
console.log('Merged profile:', user2);
console.log('Readonly user (check types):', readonlyUser);