type-fest

A collection of essential TypeScript types

Types
sindresorhus/type-festtype-fest

README



type-fest

A collection of essential TypeScript types



Sindre Sorhus' open source work is supported by the community

Special thanks to:




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Anvil

Paperwork that makes the data work.
     Easy APIs for paperwork. PDF generation, e-signature and embeddable no-code webforms.

     The easiest way to build paperwork automation into your product.
Anvil

Paperwork that makes the data work.
     Easy APIs for paperwork. PDF generation, e-signature and embeddable no-code webforms.

     The easiest way to build paperwork automation into your product.




undefined npm dependents npm downloads Docs

Many of the types here should have been built-in. You can help by suggesting some of them to the TypeScript project.

Either add this package as a dependency or copy-paste the needed types. No credit required. 👌

PR welcome for additional commonly needed types and docs improvements. Read the contributing guidelines first.

Help wanted with reviewing proposals and pull requests.

Install


  1. ```sh
  2. npm install type-fest
  3. ```

Requires TypeScript >=4.7

Usage


  1. ```ts
  2. import type {Except} from 'type-fest';

  4. type Foo = {
  5. unicorn: string;
  6. rainbow: boolean;
  7. };

  9. type FooWithoutRainbow = Except<Foo, 'rainbow'>;
  10. //=> {unicorn: string}
  11. ```

API


Click the type names for complete docs.

Basic


- [Primitive](source/primitive.d.ts) - Matches any primitive value.
- [Class](source/basic.d.ts) - Matches a [class](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes).
- [Constructor](source/basic.d.ts) - Matches a [class constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes).
- [TypedArray](source/typed-array.d.ts) - Matches any typed array, likeUint8Array or Float64Array.
- [ObservableLike](source/observable-like.d.ts) - Matches a value that is like an Observable.

Utilities


- [EmptyObject](source/empty-object.d.ts) - Represents a strictly empty plain object, the {} value.
- [IsEmptyObject](source/empty-object.d.ts) - Returns a boolean for whether the type is strictly equal to an empty plain object, the {} value.
- [Except](source/except.d.ts) - Create a type from an object type without certain keys. This is a stricter version of [Omit](https://www.typescriptlang.org/docs/handbook/utility-types.html#omittype-keys).
- [`Writable`](source/writable.d.ts) - Create a type that strips `readonly` from all or some of an object's keys. The inverse of `Readonly`.
- [Merge](source/merge.d.ts) - Merge two types into a new type. Keys of the second type overrides keys of the first type.
- [MergeDeep](source/merge-deep.d.ts) - Merge two objects or two arrays/tuples recursively into a new type.
- [MergeExclusive](source/merge-exclusive.d.ts) - Create a type that has mutually exclusive keys.
- [RequireAtLeastOne](source/require-at-least-one.d.ts) - Create a type that requires at least one of the given keys.
- [RequireExactlyOne](source/require-exactly-one.d.ts) - Create a type that requires exactly a single key of the given keys and disallows more.
- [RequireAllOrNone](source/require-all-or-none.d.ts) - Create a type that requires all of the given keys or none of the given keys.
- [OmitIndexSignature](source/omit-index-signature.d.ts) - Omit any index signatures from the given object type, leaving only explicitly defined properties.
- [PickIndexSignature](source/pick-index-signature.d.ts) - Pick only index signatures from the given object type, leaving out all explicitly defined properties.
- [`PartialDeep`](source/partial-deep.d.ts) - Create a deeply optional version of another type. Use [`Partial`](https://www.typescriptlang.org/docs/handbook/utility-types.html#partialtype) if you only need one level deep.
- [PartialOnUndefinedDeep](source/partial-on-undefined-deep.d.ts) - Create a deep version of another type where all keys accepting undefined type are set to optional.
- [`ReadonlyDeep`](source/readonly-deep.d.ts) - Create a deeply immutable version of an `object`/`Map`/`Set`/`Array` type. Use [`Readonly`](https://www.typescriptlang.org/docs/handbook/utility-types.html#readonlytype) if you only need one level deep.
- [LiteralUnion](source/literal-union.d.ts) - Create a union type by combining primitive types and literal types without sacrificing auto-completion in IDEs for the literal type part of the union. Workaround for Microsoft/TypeScript#29729.
- [Opaque](source/opaque.d.ts) - Create an opaque type.
- [UnwrapOpaque](source/opaque.d.ts) - Revert an opaque type back to its original type.
- [InvariantOf](source/invariant-of.d.ts) - Create an invariant type, which is a type that does not accept supertypes and subtypes.
- [SetOptional](source/set-optional.d.ts) - Create a type that makes the given keys optional.
- [SetRequired](source/set-required.d.ts) - Create a type that makes the given keys required.
- [SetNonNullable](source/set-non-nullable.d.ts) - Create a type that makes the given keys non-nullable.
- [ValueOf](source/value-of.d.ts) - Create a union of the given object's values, and optionally specify which keys to get the values from.
- [ConditionalKeys](source/conditional-keys.d.ts) - Extract keys from a shape where values extend the given Condition type.
- [ConditionalPick](source/conditional-pick.d.ts) - Like Pick except it selects properties from a shape where the values extend the given Condition type.
- [ConditionalPickDeep](source/conditional-pick-deep.d.ts) - Like ConditionalPick except that it selects the properties deeply.
- [ConditionalExcept](source/conditional-except.d.ts) - Like Omit except it removes properties from a shape where the values extend the given Condition type.
- [UnionToIntersection](source/union-to-intersection.d.ts) - Convert a union type to an intersection type.
- [LiteralToPrimitive](source/literal-to-primitive.d.ts) - Convert a literal type to the primitive type it belongs to.
- [Stringified](source/stringified.d.ts) - Create a type with the keys of the given type changed to string type.
- [IterableElement](source/iterable-element.d.ts) - Get the element type of an Iterable/AsyncIterable. For example, an array or a generator.
- [Entry](source/entry.d.ts) - Create a type that represents the type of an entry of a collection.
- [Entries](source/entries.d.ts) - Create a type that represents the type of the entries of a collection.
- [SetReturnType](source/set-return-type.d.ts) - Create a function type with a return type of your choice and the same parameters as the given function type.
- [Simplify](source/simplify.d.ts) - Useful to flatten the type output to improve type hints shown in editors. And also to transform an interface into a type to aide with assignability.
- [Get](source/get.d.ts) - Get a deeply-nested property from an object using a key path, like [Lodash's .get()](https://lodash.com/docs/latest#get) function.
- [StringKeyOf](source/string-key-of.d.ts) - Get keys of the given type as strings.
- [Schema](source/schema.d.ts) - Create a deep version of another object type where property values are recursively replaced into a given value type.
- [Exact](source/exact.d.ts) - Create a type that does not allow extra properties.
- [OptionalKeysOf](source/optional-keys-of.d.ts) - Extract all optional keys from the given type.
- [HasOptionalKeys](source/has-optional-keys.d.ts) - Create a true/false type depending on whether the given type has any optional fields.
- [RequiredKeysOf](source/required-keys-of.d.ts) - Extract all required keys from the given type.
- [HasRequiredKeys](source/has-required-keys.d.ts) - Create a true/false type depending on whether the given type has any required fields.
- [Spread](source/spread.d.ts) - Mimic the type inferred by TypeScript when merging two objects or two arrays/tuples using the spread syntax.

JSON


- [Jsonify](source/jsonify.d.ts) - Transform a type to one that is assignable to the JsonValue type.
- [Jsonifiable](source/jsonifiable.d.ts) - Matches a value that can be losslessly converted to JSON.
- [JsonPrimitive](source/basic.d.ts) - Matches a JSON primitive.
- [JsonObject](source/basic.d.ts) - Matches a JSON object.
- [JsonArray](source/basic.d.ts) - Matches a JSON array.
- [JsonValue](source/basic.d.ts) - Matches any valid JSON value.

Async


- [Promisable](source/promisable.d.ts) - Create a type that represents either the value or the value wrapped in PromiseLike.
- [AsyncReturnType](source/async-return-type.d.ts) - Unwrap the return type of a function that returns a Promise.
- [Asyncify](source/asyncify.d.ts) - Create an async version of the given function type.

String


- [Trim](source/trim.d.ts) - Remove leading and trailing spaces from a string.
- [Split](source/split.d.ts) - Represents an array of strings split using a given character or character set.
- [Replace](source/replace.d.ts) - Represents a string with some or all matches replaced by a replacement.

Array


- [Includes](source/includes.d.ts) - Returns a boolean for whether the given array includes the given item.
- [Join](source/join.d.ts) - Join an array of strings and/or numbers using the given string as a delimiter.
- [LastArrayElement](source/last-array-element.d.ts) - Extracts the type of the last element of an array.
- [FixedLengthArray](source/fixed-length-array.d.ts) - Create a type that represents an array of the given type and length.
- [MultidimensionalArray](source/multidimensional-array.d.ts) - Create a type that represents a multidimensional array of the given type and dimensions.
- [MultidimensionalReadonlyArray](source/multidimensional-readonly-array.d.ts) - Create a type that represents a multidimensional readonly array of the given type and dimensions.
- [ReadonlyTuple](source/readonly-tuple.d.ts) - Create a type that represents a read-only tuple of the given type and length.
- [TupleToUnion](source/tuple-to-union.d.ts) - Convert a tuple/array into a union type of its elements.

Numeric


- [PositiveInfinity](source/numeric.d.ts) - Matches the hidden Infinity type.
- [NegativeInfinity](source/numeric.d.ts) - Matches the hidden -Infinity type.
- [Finite](source/numeric.d.ts) - A finite number.
- [Integer](source/numeric.d.ts) - A number that is an integer.
- [Float](source/numeric.d.ts) - A number that is not an integer.
- [NegativeFloat](source/numeric.d.ts) - A negative (-∞ < x < 0) number that is not an integer.
- [Negative](source/numeric.d.ts) - A negative number/bigint (-∞ < x < 0)
- [NonNegative](source/numeric.d.ts) - A non-negative number/bigint (0 <= x < ∞).
- [NegativeInteger](source/numeric.d.ts) - A negative (-∞ < x < 0) number that is an integer.
- [NonNegativeInteger](source/numeric.d.ts) - A non-negative (0 <= x < ∞) number that is an integer.

Change case


- [CamelCase](source/camel-case.d.ts) - Convert a string literal to camel-case (fooBar).
- [CamelCasedProperties](source/camel-cased-properties.d.ts) - Convert object properties to camel-case (fooBar).
- [CamelCasedPropertiesDeep](source/camel-cased-properties-deep.d.ts) - Convert object properties to camel-case recursively (fooBar).
- [KebabCase](source/kebab-case.d.ts) - Convert a string literal to kebab-case (foo-bar).
- [KebabCasedProperties](source/kebab-cased-properties.d.ts) - Convert a object properties to kebab-case recursively (foo-bar).
- [KebabCasedPropertiesDeep](source/kebab-cased-properties-deep.d.ts) - Convert object properties to kebab-case (foo-bar).
- [PascalCase](source/pascal-case.d.ts) - Converts a string literal to pascal-case (FooBar)
- [PascalCasedProperties](source/pascal-cased-properties.d.ts) - Converts object properties to pascal-case (FooBar)
- [PascalCasedPropertiesDeep](source/pascal-cased-properties-deep.d.ts) - Converts object properties to pascal-case (FooBar)
- [SnakeCase](source/snake-case.d.ts) - Convert a string literal to snake-case (foo_bar).
- [SnakeCasedProperties](source/snake-cased-properties-deep.d.ts) - Convert object properties to snake-case (foo_bar).
- [SnakeCasedPropertiesDeep](source/snake-cased-properties-deep.d.ts) - Convert object properties to snake-case recursively (foo_bar).
- [ScreamingSnakeCase](source/screaming-snake-case.d.ts) - Convert a string literal to screaming-snake-case (FOO_BAR).
- [DelimiterCase](source/delimiter-case.d.ts) - Convert a string literal to a custom string delimiter casing.
- [DelimiterCasedProperties](source/delimiter-cased-properties.d.ts) - Convert object properties to a custom string delimiter casing.
- [DelimiterCasedPropertiesDeep](source/delimiter-cased-properties-deep.d.ts) - Convert object properties to a custom string delimiter casing recursively.

Miscellaneous


- [PackageJson](source/package-json.d.ts) - Type for [npm's package.json file](https://docs.npmjs.com/creating-a-package-json-file). It also includes support for TypeScript Declaration Files and Yarn Workspaces.
- [TsConfigJson](source/tsconfig-json.d.ts) - Type for [TypeScript's tsconfig.json file](https://www.typescriptlang.org/docs/handbook/tsconfig-json.html).

Declined types


If we decline a type addition, we will make sure to document the better solution here.

- [Diff and Spread](https://github.com/sindresorhus/type-fest/pull/7) - The pull request author didn't provide any real-world use-cases and the PR went stale. If you think this type is useful, provide some real-world use-cases and we might reconsider.
- [`Dictionary`](https://github.com/sindresorhus/type-fest/issues/33) - You only save a few characters (`Dictionary` vs `Record`) from [`Record`](https://www.typescriptlang.org/docs/handbook/utility-types.html#recordkeys-type), which is more flexible and well-known. Also, you shouldn't use an object as a dictionary. We have `Map` in JavaScript now.
- [ExtractProperties and ExtractMethods](https://github.com/sindresorhus/type-fest/pull/4) - The types violate the single responsibility principle. Instead, refine your types into more granular type hierarchies.
- [Url2Json](https://github.com/sindresorhus/type-fest/pull/262) - Inferring search parameters from a URL string is a cute idea, but not very useful in practice, since search parameters are usually dynamic and defined separately.
- [Nullish](https://github.com/sindresorhus/type-fest/pull/318) - The type only saves a couple of characters, not everyone knows what "nullish" means, and I'm also trying to [get away from null](https://github.com/sindresorhus/meta/discussions/7).
- [TitleCase](https://github.com/sindresorhus/type-fest/pull/303) - It's not solving a common need and is a better fit for a separate package.
- [ExtendOr and ExtendAnd](https://github.com/sindresorhus/type-fest/pull/247) - The benefits don't outweigh having to learn what they mean.
- [PackageJsonExtras](https://github.com/sindresorhus/type-fest/issues/371) - There are too many possible configurations that can be put into package.json. If you would like to extend PackageJson to support an additional configuration in your project, please see the Extending existing types section below.

Alternative type names


If you know one of our types by a different name, add it here for discovery.

- PartialBy - See [SetOptional](https://github.com/sindresorhus/type-fest/blob/main/source/set-optional.d.ts)
- RecordDeep- See [Schema](https://github.com/sindresorhus/type-fest/blob/main/source/schema.d.ts)
- Mutable- See [Writable](https://github.com/sindresorhus/type-fest/blob/main/source/writable.d.ts)

Tips


Extending existing types


- [PackageJson](source/package-json.d.ts) - There are a lot of tools that place extra configurations inside the package.json file. You can extend PackageJson to support these additional configurations.
   Example

Playground

ts
import type {PackageJson as BasePackageJson} from 'type-fest';
import type {Linter} from 'eslint';

type PackageJson = BasePackageJson & {eslintConfig?: Linter.Config};

Related


- typed-query-selector - Enhancesdocument.querySelector and document.querySelectorAll with a template literal type that matches element types returned from an HTML element query selector.
- [Linter.Config](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/eslint/index.d.ts) - Definitions for the ESLint configuration schema.

Built-in types


There are many advanced types most users don't know about.

- [`Partial`](https://www.typescriptlang.org/docs/handbook/utility-types.html#partialtype) - Make all properties in `T` optional.
   Example

Playground

ts
interface NodeConfig {
   appName: string;
   port: number;
}

class NodeAppBuilder {
   private configuration: NodeConfig = {
     appName: 'NodeApp',
     port: 3000
   };

private updateConfig(key: Key, value: NodeConfig[Key]) {
     this.configuration[key] = value;
   }

config(config: Partial) {
     type NodeConfigKey = keyof NodeConfig;

     for (const key of Object.keys(config) as NodeConfigKey[]) {
       const updateValue = config[key];

       if (updateValue === undefined) {
         continue;
       }

       this.updateConfig(key, updateValue);
     }

     return this;
   }
}

// `Partial`` allows us to provide only a part of the
// NodeConfig interface.
new NodeAppBuilder().config({appName: 'ToDoApp'});

- [`Required`](https://www.typescriptlang.org/docs/handbook/utility-types.html#requiredtype) - Make all properties in `T` required.
   Example

Playground

ts
interface ContactForm {
   email?: string;
   message?: string;
}

function submitContactForm(formData: Required) {
   // Send the form data to the server.
}

submitContactForm({
   email: 'ex@mple.com',
   message: 'Hi! Could you tell me more about…',
});

// TypeScript error: missing property 'message'
submitContactForm({
   email: 'ex@mple.com',
});

- [`Readonly`](https://www.typescriptlang.org/docs/handbook/utility-types.html#readonlytype) - Make all properties in `T` readonly.
   Example

Playground

ts
enum LogLevel {
   Off,
   Debug,
   Error,
   Fatal
};

interface LoggerConfig {
   name: string;
   level: LogLevel;
}

class Logger {
config: Readonly;

   constructor({name, level}: LoggerConfig) {
     this.config = {name, level};
     Object.freeze(this.config);
   }
}

const config: LoggerConfig = {
  name: 'MyApp',
  level: LogLevel.Debug
};

const logger = new Logger(config);

// TypeScript Error: cannot assign to read-only property.
logger.config.level = LogLevel.Error;

// We are able to edit config variable as we please.
config.level = LogLevel.Error;

- [`Pick`](https://www.typescriptlang.org/docs/handbook/utility-types.html#picktype-keys) - From `T`, pick a set of properties whose keys are in the union `K`.
   Example

Playground

ts
interface Article {
   title: string;
   thumbnail: string;
   content: string;
}

// Creates new type out of the Article interface composed
// from the Articles' two properties: title and thumbnail.
// ArticlePreview = {title: string; thumbnail: string}
type ArticlePreview = Pick;

// Render a list of articles using only title and description.
function renderArticlePreviews(previews: ArticlePreview[]): HTMLElement {
   const articles = document.createElement('div');

   for (const preview of previews) {
     // Append preview to the articles.
   }

   return articles;
}

const articles = renderArticlePreviews([
   {
    title: 'TypeScript tutorial!',
    thumbnail: '/assets/ts.jpg'
   }
]);

- [`Record`](https://www.typescriptlang.org/docs/handbook/utility-types.html#recordkeys-type) - Construct a type with a set of properties `K` of type `T`.
   Example

Playground

ts
// Positions of employees in our company.
type MemberPosition = 'intern' | 'developer' | 'tech-lead';

// Interface describing properties of a single employee.
interface Employee {
   firstName: string;
   lastName: string;
   yearsOfExperience: number;
}

// Create an object that has all possible MemberPosition values set as keys.
// Those keys will store a collection of Employees of the same position.
const team: Record = {
   intern: [],
   developer: [],
   'tech-lead': [],
};

// Our team has decided to help John with his dream of becoming Software Developer.
team.intern.push({
  firstName: 'John',
  lastName: 'Doe',
  yearsOfExperience: 0
});

// Record forces you to initialize all of the property keys.
// TypeScript Error: "tech-lead" property is missing
const teamEmpty: Record = {
   intern: null,
   developer: null,
};

- [`Exclude`](https://www.typescriptlang.org/docs/handbook/utility-types.html#excludetype-excludedunion) - Exclude from `T` those types that are assignable to `U`.
   Example

Playground

ts
interface ServerConfig {
  port: null | string | number;
}

type RequestHandler = (request: Request, response: Response) => void;

// Exclude null type from null | string | number.
// In case the port is equal to null, we will use default value.
function getPortValue(port: Exclude): number {
  if (typeof port === 'string') {
   return parseInt(port, 10);
  }

  return port;
}

function startServer(handler: RequestHandler, config: ServerConfig): void {
  const server = require('http').createServer(handler);

  const port = config.port === null ? 3000 : getPortValue(config.port);
  server.listen(port);
}

- [`Extract`](https://www.typescriptlang.org/docs/handbook/utility-types.html#extracttype-union) - Extract from `T` those types that are assignable to `U`.
   Example

Playground

ts
declare function uniqueId(): number;

const ID = Symbol('ID');

interface Person {
  [ID]: number;
  name: string;
  age: number;
}

// Allows changing the person data as long as the property key is of string type.
function changePersonData<
  Obj extends Person,
Key extends Extract,
  Value extends Obj[Key]
> (obj: Obj, key: Key, value: Value): void {
  obj[key] = value;
}

// Tiny Andrew was born.
const andrew = {
  [ID]: uniqueId(),
  name: 'Andrew',
  age: 0,
};

// Cool, we're fine with that.
changePersonData(andrew, 'name', 'Pony');

// Goverment didn't like the fact that you wanted to change your identity.
changePersonData(andrew, ID, uniqueId());

- [`NonNullable`](https://www.typescriptlang.org/docs/handbook/utility-types.html#nonnullabletype) - Exclude `null` and `undefined` from `T`.
   Example
 Works with strictNullChecks set to true.

Playground

ts
type PortNumber = string | number | null;

/* Part of a class definition that is used to build a server /
class ServerBuilder {
portNumber!: NonNullable;

   port(this: ServerBuilder, port: PortNumber): ServerBuilder {
     if (port == null) {
       this.portNumber = 8000;
     } else {
       this.portNumber = port;
     }

     return this;
   }
}

const serverBuilder = new ServerBuilder();

serverBuilder
   .port('8000')   // portNumber = '8000'
   .port(null)     // portNumber =  8000
   .port(3000);    // portNumber =  3000

// TypeScript error
serverBuilder.portNumber = null;

- [`Parameters`](https://www.typescriptlang.org/docs/handbook/utility-types.html#parameterstype) - Obtain the parameters of a function type in a tuple.
   Example

Playground

ts
function shuffle(input: any[]): void {
  // Mutate array randomly changing its' elements indexes.
}

function callNTimes any> (func: Fn, callCount: number) {
  // Type that represents the type of the received function parameters.
type FunctionParameters = Parameters;

  return function (...args: FunctionParameters) {
   for (let i = 0; i < callCount; i++) {
    func(...args);
   }
  }
}

const shuffleTwice = callNTimes(shuffle, 2);

- [`ConstructorParameters`](https://www.typescriptlang.org/docs/handbook/utility-types.html#constructorparameterstype) - Obtain the parameters of a constructor function type in a tuple.
   Example

Playground

ts
class ArticleModel {
  title: string;
  content?: string;

  constructor(title: string) {
   this.title = title;
  }
}

class InstanceCache any)> {
  private ClassConstructor: T;
private cache: Map> = new Map();

  constructor (ctr: T) {
   this.ClassConstructor = ctr;
  }

getInstance (...args: ConstructorParameters): InstanceType {
   const hash = this.calculateArgumentsHash(...args);

   const existingInstance = this.cache.get(hash);
   if (existingInstance !== undefined) {
    return existingInstance;
   }

   return new this.ClassConstructor(...args);
  }

  private calculateArgumentsHash(...args: any[]): string {
   // Calculate hash.
   return 'hash';
  }
}

const articleCache = new InstanceCache(ArticleModel);
const amazonArticle = articleCache.getInstance('Amazon forests burining!');

- [`ReturnType`](https://www.typescriptlang.org/docs/handbook/utility-types.html#returntypetype) - Obtain the return type of a function type.
   Example

Playground

ts
/* Provides every element of the iterable iter into the callback function and stores the results in an array. /
function mapIter<
   Elem,
   Func extends (elem: Elem) => any,
Ret extends ReturnType >(iter: Iterable, callback: Func): Ret[] {
   const mapped: Ret[] = [];

   for (const elem of iter) {
     mapped.push(callback(elem));
   }

   return mapped;
}

const setObject: Set = new Set(); const mapObject: Map = new Map();

mapIter(setObject, (value: string) => value.indexOf('Foo')); // number[]

mapIter(mapObject, ([key, value]: [number, string]) => {
   return key % 2 === 0 ? value : 'Odd';
}); // string[]

- [`InstanceType`](https://www.typescriptlang.org/docs/handbook/utility-types.html#instancetypetype) - Obtain the instance type of a constructor function type.
   Example

Playground

ts
class IdleService {
   doNothing (): void {}
}

class News {
   title: string;
   content: string;

   constructor(title: string, content: string) {
     this.title = title;
     this.content = content;
   }
}

const instanceCounter: Map = new Map();

interface Constructor {
   new(...args: any[]): any;
}

// Keep track how many instances of Constr constructor have been created.
function getInstance<
   Constr extends Constructor,
Args extends ConstructorParameters >(constructor: Constr, ...args: Args): InstanceType {
   let count = instanceCounter.get(constructor) || 0;

   const instance = new constructor(...args);

   instanceCounter.set(constructor, count + 1);

   console.log(Created ${count + 1} instances of ${Constr.name} class);

   return instance;
}


const idleService = getInstance(IdleService);
// Will log: Created 1 instances of IdleService class
const newsEntry = getInstance(News, 'New ECMAScript proposals!', 'Last month...');
// Will log: Created 1 instances of News class

- [`Omit`](https://www.typescriptlang.org/docs/handbook/utility-types.html#omittype-keys) - Constructs a type by picking all properties from T and then removing K.
   Example

Playground

ts
interface Animal {
   imageUrl: string;
   species: string;
   images: string[];
   paragraphs: string[];
}

// Creates new type with all properties of the Animal interface
// except 'images' and 'paragraphs' properties. We can use this
// type to render small hover tooltip for a wiki entry list.
type AnimalShortInfo = Omit;

function renderAnimalHoverInfo (animals: AnimalShortInfo[]): HTMLElement {
   const container = document.createElement('div');
   // Internal implementation.
   return container;
}

- [`Uppercase`](https://www.typescriptlang.org/docs/handbook/utility-types.html#uppercasestringtype) - Transforms every character in a string into uppercase.
  Example

ts
type T = Uppercase<'hello'>; // 'HELLO'

type T2 = Uppercase<'foo' | 'bar'>; // 'FOO' | 'BAR'

type T3 = Uppercase<`aB${S}`>; type T4 = T3<'xYz'>; // 'ABXYZ'

type T5 = Uppercase; // string type T6 = Uppercase; // any type T7 = Uppercase; // never type T8 = Uppercase<42>; // Error, type 'number' does not satisfy the constraint 'string'

- [`Lowercase`](https://www.typescriptlang.org/docs/handbook/utility-types.html#lowercasestringtype) - Transforms every character in a string into lowercase.
  Example

ts
type T = Lowercase<'HELLO'>; // 'hello'

type T2 = Lowercase<'FOO' | 'BAR'>; // 'foo' | 'bar'

type T3 = Lowercase<`aB${S}`>; type T4 = T3<'xYz'>; // 'abxyz'

type T5 = Lowercase; // string type T6 = Lowercase; // any type T7 = Lowercase; // never type T8 = Lowercase<42>; // Error, type 'number' does not satisfy the constraint 'string'

- [`Capitalize`](https://www.typescriptlang.org/docs/handbook/utility-types.html#capitalizestringtype) - Transforms the first character in a string into uppercase.
  Example

ts
type T = Capitalize<'hello'>; // 'Hello'

type T2 = Capitalize<'foo' | 'bar'>; // 'Foo' | 'Bar'

type T3 = Capitalize<`aB${S}`>; type T4 = T3<'xYz'>; // 'ABxYz'

type T5 = Capitalize; // string type T6 = Capitalize; // any type T7 = Capitalize; // never type T8 = Capitalize<42>; // Error, type 'number' does not satisfy the constraint 'string'

- [`Uncapitalize`](https://www.typescriptlang.org/docs/handbook/utility-types.html#uncapitalizestringtype) - Transforms the first character in a string into lowercase.
  Example

ts
type T = Uncapitalize<'Hello'>; // 'hello'

type T2 = Uncapitalize<'Foo' | 'Bar'>; // 'foo' | 'bar'

type T3 = Uncapitalize<`AB${S}`>; type T4 = T3<'xYz'>; // 'aBxYz'

type T5 = Uncapitalize; // string type T6 = Uncapitalize; // any type T7 = Uncapitalize; // never type T8 = Uncapitalize<42>; // Error, type 'number' does not satisfy the constraint 'string'

You can find some examples in the TypeScript docs.

Maintainers


- Sindre Sorhus
- Jarek Radosz
- Dimitri Benin
- Pelle Wessman
- Sébastien Mischler

License


SPDX-License-Identifier: (MIT OR CC0-1.0)