+++ /dev/null
-<div align="center">
- <br>
- <br>
- <img src="media/logo.svg" alt="type-fest" height="300">
- <br>
- <br>
- <b>A collection of essential TypeScript types</b>
- <br>
- <hr>
-</div>
-<br>
-<br>
-
-[](https://travis-ci.com/sindresorhus/type-fest)
-[](https://www.youtube.com/watch?v=9auOCbH5Ns4)
-<!-- Commented out until they actually show anything
-[](https://www.npmjs.com/package/type-fest?activeTab=dependents) [](https://www.npmjs.com/package/type-fest)
--->
-
-Many of the types here should have been built-in. You can help by suggesting some of them to the [TypeScript project](https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md).
-
-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](.github/contributing.md) first.
-
-
-## Install
-
-```
-$ npm install type-fest
-```
-
-*Requires TypeScript >=3.2*
-
-
-## Usage
-
-```ts
-import {Except} from 'type-fest';
-
-type Foo = {
- unicorn: string;
- rainbow: boolean;
-};
-
-type FooWithoutRainbow = Except<Foo, 'rainbow'>;
-//=> {unicorn: string}
-```
-
-
-## API
-
-Click the type names for complete docs.
-
-### Basic
-
-- [`Primitive`](source/basic.d.ts) - Matches any [primitive value](https://developer.mozilla.org/en-US/docs/Glossary/Primitive).
-- [`Class`](source/basic.d.ts) - Matches a [`class` constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes).
-- [`TypedArray`](source/basic.d.ts) - Matches any [typed array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), like `Uint8Array` or `Float64Array`.
-- [`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.
-- [`ObservableLike`](source/basic.d.ts) - Matches a value that is like an [Observable](https://github.com/tc39/proposal-observable).
-
-### Utilities
-
-- [`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/release-notes/typescript-3-5.html#the-omit-helper-type).
-- [`Mutable`](source/mutable.d.ts) - Convert an object with `readonly` keys into a mutable object. The inverse of `Readonly<T>`.
-- [`Merge`](source/merge.d.ts) - Merge two types into a new type. Keys of the second type overrides keys of the first 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-one.d.ts) - Create a type that requires exactly a single key of the given keys and disallows more.
-- [`PartialDeep`](source/partial-deep.d.ts) - Create a deeply optional version of another type. Use [`Partial<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1401-L1406) if you only need one level deep.
-- [`ReadonlyDeep`](source/readonly-deep.d.ts) - Create a deeply immutable version of an `object`/`Map`/`Set`/`Array` type. Use [`Readonly<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1415-L1420) 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](https://github.com/Microsoft/TypeScript/issues/29729).
-- [`Promisable`](source/promisable.d.ts) - Create a type that represents either the value or the value wrapped in `PromiseLike`.
-- [`Opaque`](source/opaque.d.ts) - Create an [opaque type](https://codemix.com/opaque-types-in-javascript/).
-- [`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.
-
-### Miscellaneous
-
-- [`PackageJson`](source/package-json.d.ts) - Type for [npm's `package.json` file](https://docs.npmjs.com/creating-a-package-json-file).
-
-
-## 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 PR 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<number>` vs `Record<string, number>`) from [`Record`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1429-L1434), which is more flexible and well-known. Also, you shouldn't use an object as a dictionary. We have `Map` in JavaScript now.
-
-
-## Tips
-
-### Built-in types
-
-There are many advanced types most users don't know about.
-
-- [`Partial<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1401-L1406) - Make all properties in `T` optional.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#code/KYOwrgtgBAMg9gcxsAbsANlA3gKClAeQDMiAaPKAEWACMwFz8BRAJxbhcagDEBDAF17ocAXxw4AliH7AWRXgGNgUAHJwAJsADCcEEQkJsFXgAcTK3hGAAuKAGd+LKQgDcFEx363wEGrLf46IjIaOi28EioGG5iOArovHZ2qhrAAIJmAEJgEuiaLEb4Jk4oAsoKuvoIYCwCErq2apo6egZQALyF+FCm5pY2UABETelmg1xFnrYAzAAM8xNQQZGh4cFR6AB0xEQUIm4UFa0IABRHVbYACrws-BJCADwjLVUAfACUXfhEHFBnug4oABrYAATygcCIhBoACtgAp+JsQaC7P9ju9Prhut0joCwCZ1GUAGpCMDKTrnAwAbWRPWSyMhKWalQMAF0Dtj8BIoSd8YSZCT0GSOu1OmAQJp9CBgOpPkc7uBgBzOfwABYSOybSnVWp3XQ0sF04FgxnPFkIVkdKB84mkpUUfCxbEsYD8GogKBqjUBKBiWIAen9UGut3u6CeqReBlePXQQQA7skwMl+HAoMU4CgJJoISB0ODeOmbvwIVC1cAcIGmdpzVApDI5IpgJscNL49WMiZsrl8id3lrzScsD0zBYrLZBgAVOCUOCdwa+95uIA)
-
- ```ts
- interface NodeConfig {
- appName: string;
- port: number;
- }
-
- class NodeAppBuilder {
- private configuration: NodeConfig = {
- appName: 'NodeApp',
- port: 3000
- };
-
- config(config: Partial<NodeConfig>) {
- type NodeConfigKey = keyof NodeConfig;
-
- for (const key of Object.keys(config) as NodeConfigKey[]) {
- const updateValue = config[key];
-
- if (updateValue === undefined) {
- continue;
- }
-
- this.configuration[key] = updateValue;
- }
-
- return this;
- }
- }
-
- // `Partial<NodeConfig>`` allows us to provide only a part of the
- // NodeConfig interface.
- new NodeAppBuilder().config({appName: 'ToDoApp'});
- ```
- </details>
-
-- [`Required<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1408-L1413) - Make all properties in `T` required.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#code/AQ4SwOwFwUwJwGYEMDGNgGED21VQGJZwC2wA3gFCjXAzFJgA2A-AFzADOUckA5gNxUaIYjA4ckvGG07c+g6gF8KQkAgCuEFFDA5O6gEbEwUbLm2ESwABQIixACJIoSdgCUYAR3Vg4MACYAPGYuFvYAfACU5Ko0APRxwADKMBD+wFAAFuh2Vv7OSBlYGdmc8ABu8LHKsRyGxqY4oQT21pTCIHQMjOwA5DAAHgACxAAOjDAAdChYxL0ANLHUouKSMH0AEmAAhJhY6ozpAJ77GTCMjMCiV0ToSAb7UJPPC9WRgrEJwAAqR6MwSRQPFGUFocDgRHYxnEfGAowh-zgUCOwF6KwkUl6tXqJhCeEsxDaS1AXSYfUGI3GUxmc0WSneQA)
-
- ```ts
- interface ContactForm {
- email?: string;
- message?: string;
- }
-
- function submitContactForm(formData: Required<ContactForm>) {
- // 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',
- });
- ```
- </details>
-
-- [`Readonly<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1415-L1420) - Make all properties in `T` readonly.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#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)
-
- ```ts
- enum LogLevel {
- Off,
- Debug,
- Error,
- Fatal
- };
-
- interface LoggerConfig {
- name: string;
- level: LogLevel;
- }
-
- class Logger {
- config: Readonly<LoggerConfig>;
-
- 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;
- ```
- </details>
-
-- [`Pick<T, K>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1422-L1427) - From `T`, pick a set of properties whose keys are in the union `K`.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#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)
-
- ```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<Article, 'title' | 'thumbnail'>;
-
- // 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'
- }
- ]);
- ```
- </details>
-
-- [`Record<K, T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1429-L1434) - Construct a type with a set of properties `K` of type `T`.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#code/AQ4ejYAUHsGcCWAXBMB2dgwGbAKYC2ADgDYwCeeemCaWArgE7ADGMxAhmuQHQBQoYEnJE8wALKEARnkaxEKdMAC8wAOS0kstGuAAfdQBM8ANzxlRjXQbVaWACwC0JPB0NqA3HwGgIwAJJoWozYHCxixnAsjAhStADmwESMMJYo1Fi4HMCIaPEu+MRklHj8gpqyoeHAAKJFFFTAAN4+giDYCIxwSAByHAR4AFw5SDF5Xm2gJBzdfQPD3WPxE5PAlBxdAPLYNQAelgh4aOHDaPQEMowrIAC+3oJ+AMKMrlrAXFhSAFZ4LEhC9g4-0BmA4JBISXgiCkBQABpILrJ5MhUGhYcATGD6Bk4Hh-jNgABrPDkOBlXyQAAq9ngYmJpOAAHcEOCRjAXqwYODfoo6DhakUSph+Uh7GI4P0xER4Cj0OSQGwMP8tP1hgAlX7swwAHgRl2RvIANALSA08ABtAC6AD4VM1Wm0Kow0MMrYaHYJjGYLLJXZb3at1HYnC43Go-QHQDcvA6-JsmEJXARgCDgMYWAhjIYhDAU+YiMAAFIwex0ZmilMITCGF79TLAGRsAgJYAAZRwSEZGzEABFTOZUrJ5Yn+jwnWgeER6HB7AAKJrADpdXqS4ZqYultTG6azVfqHswPBbtauLY7fayQ7HIbAAAMwBuAEoYw9IBq2Ixs9h2eFMOQYPQObALQKJgggABeYhghCIpikkKRpOQRIknAsZUiIeCttECBEP8NSMCkjDDAARMGziuIYxHwYOjDCMBmDNnAuTxA6irdCOBB1Lh5Dqpqn66tISIykawBnOCtqqC0gbjqc9DgpGkxegOliyfJDrRkAA)
-
- ```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<MemberPosition, Employee[]> = {
- 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<MemberPosition, null> = {
- intern: null,
- developer: null,
- };
- ```
- </details>
-
-- [`Exclude<T, U>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1436-L1439) - Exclude from `T` those types that are assignable to `U`.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#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)
-
- ```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<ServerConfig['port'], null>): 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);
- }
- ```
- </details>
-
-- [`Extract<T, U>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1441-L1444) - Extract from `T` those types that are assignable to `U`.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXzSwEdkQBJYACgEoAueVZAWwCMQYBuAKDDwGcM8MgBF4AXngBlAJ6scESgHIRi6ty5ZUGdoihgEABXZ888AN5d48ANoiAuvUat23K6ihMQ9ATE0BzV3goPy8GZjZOLgBfLi4Aejj4AEEICBwAdz54MAALKFQQ+BxEeAAHY1NgKAwoIKy0grr4DByEUpgccpgMaXgAaxBerCzi+B9-ZulygDouFHRsU1z8kKMYE1RhaqgAHkt4AHkWACt4EAAPbVRgLLWNgBp9gGlBs8uQa6yAUUuYPQwdgNpKM7nh7mMML4CgA+R5WABqUAgpDeVxuhxO1he0jsXGh8EoOBO9COx3BQPo2PBADckaR6IjkSA6PBqTgsMBzPsicdrEC7OJWXSQNwYvFEgAVTS9JLXODpeDpKBZFg4GCoWa8VACIJykAKiQWKy2YQOAioYikCg0OEMDyhRSy4DyxS24KhAAMjyi6gS8AAwjh5OD0iBFHAkJoEOksC1mnkMJq8gUQKDNttKPlnfrwYp3J5XfBHXqoKpfYkAOI4ansTxaeDADmoRSCCBYAbxhC6TDx6rwYHIRX5bScjA4bLJwoDmDwDkfbA9JMrVMVdM1TN69LgkTgwgkchUahqIA)
-
- ```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<keyof Person, string>,
- 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());
- ```
- </details>
-
-- [`NonNullable<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1446-L1449) - Exclude `null` and `undefined` from `T`.
- <details>
- <summary>
- Example
- </summary>
- Works with <code>strictNullChecks</code> set to <code>true</code>. (Read more <a href="https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html">here</a>)
-
- [Playground](https://typescript-play.js.org/?target=6#code/C4TwDgpgBACg9gJ2AOQK4FsBGEFQLxQDOwCAlgHYDmUAPlORtrnQwDasDcAUFwPQBU-WAEMkUOADMowqAGNWwwoSgATCBIqlgpOOSjAAFsOBRSy1IQgr9cKJlSlW1mZYQA3HFH68u8xcoBlHA8EACEHJ08Aby4oKDBUTFZSWXjEFEYcAEIALihkXTR2YSSIAB54JDQsHAA+blj4xOTUsHSACkMzPKD3HHDHNQQAGjSkPMqMmoQASh7g-oihqBi4uNIpdraxPAI2VhmVxrX9AzMAOm2ppnwoAA4ABifuE4BfKAhWSyOTuK7CS7pao3AhXF5rV48E4ICDAVAIPT-cGQyG+XTEIgLMJLTx7CAAdygvRCA0iCHaMwarhJOIQjUBSHaACJHk8mYdeLwxtdcVAAOSsh58+lXdr7Dlcq7A3n3J4PEUdADMcspUE53OluAIUGVTx46oAKuAIAFZGQwCYAKIIBCILjUxaDHAMnla+iodjcIA)
-
- ```ts
- type PortNumber = string | number | null;
-
- /** Part of a class definition that is used to build a server */
- class ServerBuilder {
- portNumber!: NonNullable<PortNumber>;
-
- 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;
- ```
- </details>
-
-- [`Parameters<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1451-L1454) - Obtain the parameters of a function type in a tuple.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#code/GYVwdgxgLglg9mABAZwBYmMANgUwBQxgAOIUAXIgIZgCeA2gLoCUFAbnDACaIDeAUIkQB6IYgCypSlBxUATrMo1ECsJzgBbLEoipqAc0J7EMKMgDkiHLnU4wp46pwAPHMgB0fAL58+oSLARECEosLAA5ABUYG2QAHgAxJGdpVWREPDdMylk9ZApqemZEAF4APipacrw-CApEgBogkKwAYThwckQwEHUAIxxZJl4BYVEImiIZKF0oZRwiWVdbeygJmThgOYgcGFYcbhqApCJsyhtpWXcR1cnEePBoeDAABVPzgbTixFeFd8uEsClADcIxGiygIFkSEOT3SmTc2VydQeRx+ZxwF2QQ34gkEwDgsnSuFmMBKiAADEDjIhYk1Qm0OlSYABqZnYka4xA1DJZHJYkGc7yCbyeRA+CAIZCzNAYbA4CIAdxg2zJwVCkWirjwMswuEaACYmCCgA)
-
- ```ts
- function shuffle(input: any[]): void {
- // Mutate array randomly changing its' elements indexes.
- }
-
- function callNTimes<Fn extends (...args: any[]) => any> (func: Fn, callCount: number) {
- // Type that represents the type of the received function parameters.
- type FunctionParameters = Parameters<Fn>;
-
- return function (...args: FunctionParameters) {
- for (let i = 0; i < callCount; i++) {
- func(...args);
- }
- }
- }
-
- const shuffleTwice = callNTimes(shuffle, 2);
- ```
- </details>
-
-- [`ConstructorParameters<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1456-L1459) - Obtain the parameters of a constructor function type in a tuple.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#code/MYGwhgzhAECCBOAXAlqApgWQPYBM0mgG8AoaaFRENALmgkXmQDsBzAblOmCycTV4D8teo1YdO3JiICuwRFngAKClWENmLAJRFOZRAAtkEAHQq00ALzlklNBzIBfYk+KhIMAJJTEYJsDQAwmDA+mgAPAAq0GgAHnxMODCKTGgA7tCKxllg8CwQtL4AngDaALraFgB80EWa1SRkAA6MAG5gfNAB4FABPDJyCrQR9tDNyG0dwMGhtBhgjWEiGgA00F70vv4RhY3hEZXVVinpc42KmuJkkv3y8Bly8EPaDWTkhiZd7r3e8LK3llwGCMXGQWGhEOsfH5zJlsrl8p0+gw-goAAo5MAAW3BaHgEEilU0tEhmzQ212BJ0ry4SOg+kg+gBBiMximIGA0nAfAQLGk2N4EAAEgzYcYcnkLsRdDTvNEYkYUKwSdCme9WdM0MYwYhFPSIPpJdTkAAzDKxBUaZX+aAAQgsVmkCTQxuYaBw2ng4Ok8CYcotSu8pMur09iG9vuObxZnx6SN+AyUWTF8MN0CcZE4Ywm5jZHK5aB5fP4iCFIqT4oRRTKRLo6lYVNeAHpG50wOzOe1zHr9NLQ+HoABybsD4HOKXXRA1JCoKhBELmI5pNaB6Fz0KKBAodDYPAgSUTmqYsAALx4m5nC6nW9nGq14KtaEUA9gR9PvuNCjQ9BgACNvcwNBtAcLiAA)
-
- ```ts
- class ArticleModel {
- title: string;
- content?: string;
-
- constructor(title: string) {
- this.title = title;
- }
- }
-
- class InstanceCache<T extends (new (...args: any[]) => any)> {
- private ClassConstructor: T;
- private cache: Map<string, InstanceType<T>> = new Map();
-
- constructor (ctr: T) {
- this.ClassConstructor = ctr;
- }
-
- getInstance (...args: ConstructorParameters<T>): InstanceType<T> {
- 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!');
- ```
- </details>
-
-- [`ReturnType<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1461-L1464) – Obtain the return type of a function type.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#code/MYGwhgzhAECSAmICmBlJAnAbgS2E6A3gFDTTwD2AcuQC4AW2AdgOYAUAlAFzSbnbyEAvkWFFQkGJSQB3GMVI1sNZNwg10TZgG4S0YOUY0kh1es07d+xmvQBXYDXLpWi5UlMaWAGj0GjJ6BtNdkJdBQYIADpXZGgAXmgYpB1ScOwoq38aeN9DYxoU6GFRKzVoJjUwRjwAYXJbPPRuAFkwAAcAHgAxBodsAx9GWwBbACMMAD4cxhloVraOCyYjdAAzMDxoOut1e0d0UNIZ6WhWSPOwdGYIbiqATwBtAF0uaHudUQB6ACpv6ABpJBINqJdAbADW0Do5BOw3u5R2VTwMHIq2gAANtjZ0bkbHsnFCwJh8ONjHp0EgwEZ4JFoN9PkRVr1FAZoMwkDRYIjqkgOrosepoEgAB7+eAwAV2BxOLy6ACCVxgIrFEoMeOl6AACpcwMMORgIB1JRMiBNWKVdhruJKfOdIpdrtwFddXlzKjyACp3Nq842HaDIbL6BrZBIVGhIpB1EMYSLsmjmtWW-YhAA+qegAAYLKQLQj3ZsEsdccmnGcLor2Dn8xGedHGpEIBzEzspfsfMHDNAANTQACMVaIljV5GQkRA5DYmIpVKQAgAJARO9le33BDXIyi0YuLW2nJFGLqkOvxFB0YPdBSaLZ0IwNzyPkO8-xkGgsLh8Al427a3hWAhXwwHA8EHT5PmgAB1bAQBAANJ24adKWpft72RaBUTgRBUCAj89HAM8xCTaBjggABRQx0DuHJv25P9dCkWRZVIAAiBjoFImpmjlFBgA0NpsjadByDacgIDAEAIAAQmYpjoGYgAZSBsmGPw6DtZiiFA8CoJguDmAQmoZ2QvtUKQLdoAYmBTwgdEiCAA)
-
- ```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<Func>
- >(iter: Iterable<Elem>, callback: Func): Ret[] {
- const mapped: Ret[] = [];
-
- for (const elem of iter) {
- mapped.push(callback(elem));
- }
-
- return mapped;
- }
-
- const setObject: Set<string> = new Set();
- const mapObject: Map<number, string> = new Map();
-
- mapIter(setObject, (value: string) => value.indexOf('Foo')); // number[]
-
- mapIter(mapObject, ([key, value]: [number, string]) => {
- return key % 2 === 0 ? value : 'Odd';
- }); // string[]
- ```
- </details>
-
-- [`InstanceType<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1466-L1469) – Obtain the instance type of a constructor function type.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#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-YhAA+qegAAYLKQLQj3ZsEsdccmnGcLor2Dn8xGedHGpEIBzEzspfsfMHDNAANTQACMVaIljV5GQkRA5DYmIpVKQAgAJARO9le33BDXIyi0YuLW2nJFGLqkOvxFB0YPdBSaLZ0IwNzyPkO8-xkGgsLh8Al427a3hWAhXwwHA8EHT5PmgAB1bAQBAANJ24adKWpft72RaBUTgRBUCAj89HAM8xCTaBjggABRQx0DuHJv25P9dCkWRZVIAAiBjoFImpmjlFBgA0NpsjadByDacgIDAEAIAAQmYpjoGYgAZSBsmGPw6DtZiiFA8CoJguDmAQmoZ2QvtUKQLdoAYmBTwgdEiCAA)
-
- ```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<Function, number> = 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<Constr>
- >(constructor: Constr, ...args: Args): InstanceType<Constr> {
- 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`
- ```
- </details>
-
-- [`Omit<T, K>`](https://github.com/microsoft/TypeScript/blob/71af02f7459dc812e85ac31365bfe23daf14b4e4/src/lib/es5.d.ts#L1446) – Constructs a type by picking all properties from T and then removing K.
- <details>
- <summary>
- Example
- </summary>
-
- [Playground](https://typescript-play.js.org/?target=6#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-SgfXlHqVUE4xiAA)
-
- ```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<Animal, 'images' | 'paragraphs'>;
-
- function renderAnimalHoverInfo (animals: AnimalShortInfo[]): HTMLElement {
- const container = document.createElement('div');
- // Internal implementation.
- return container;
- }
- ```
- </details>
-
-You can find some examples in the [TypeScript docs](https://www.typescriptlang.org/docs/handbook/advanced-types.html#predefined-conditional-types).
-
-
-## Maintainers
-
-- [Sindre Sorhus](https://github.com/sindresorhus)
-- [Jarek Radosz](https://github.com/CvX)
-- [Dimitri Benin](https://github.com/BendingBender)
-
-
-## License
-
-(MIT OR CC0-1.0)
-
-
----
-
-<div align="center">
- <b>
- <a href="https://tidelift.com/subscription/pkg/npm-type-fest?utm_source=npm-type-fest&utm_medium=referral&utm_campaign=readme">Get professional support for this package with a Tidelift subscription</a>
- </b>
- <br>
- <sub>
- Tidelift helps make open source sustainable for maintainers while giving companies<br>assurances about security, maintenance, and licensing for their dependencies.
- </sub>
-</div>
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