StrictExtract<BaseType, Subset>

Overview

This type is stricter version of TypeScript's Extract utility type.

Unlike Extract, which allows extraction of members not present on the given type, StrictExtract ensures that only members actually present in the type can be extracted.

Syntax

export type StrictExtract<BaseType, Subset extends BaseType> = Extract<
  BaseType,
  Subset
>;

• BaseType: The type from which you want to extract union members.
• Subset: The members or types that you want to extract from the BaseType.

Examples

Example #1

type Example = 'admin' | 'editor' | 'viewer';
type StrictExtractedExample = StrictExtract<Example, 'admin' | 'editor'>;
// Result: "admin" | "editor"

TIP

If your team is using ESLint and wants to enforce the use of StrictExtract instead of the standard Extract, you can configure ESLint to help catch this. The @typescript-eslint/ban-types rule can be configured to display an error message when Extract is used, guiding developers to use StrictExtract instead. Here's how you can set up your ESLint configuration:

module.exports = {
  parser: '@typescript-eslint/parser',
  plugins: ['@typescript-eslint'],
  rules: {
    // Include other relevant rules here
    '@typescript-eslint/ban-types': [
      'error',
      {
        types: {
          Extract: 'Use StrictExtract instead',
        },
        extendsDefaults: true,
      },
    ],
  },
};