760 lines
33 KiB
Markdown
760 lines
33 KiB
Markdown
<div align="center">
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<br>
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<br>
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<img src="media/logo.svg" alt="type-fest" height="300">
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<br>
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<br>
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<b>A collection of essential TypeScript types</b>
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<br>
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<br>
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<br>
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<br>
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<div align="center">
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<p>
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<p>
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<sup>
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<a href="https://github.com/sponsors/sindresorhus">Sindre Sorhus' open source work is supported by the community</a>
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</sup>
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</p>
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<sup>Special thanks to:</sup>
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<br>
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<br>
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<a href="https://standardresume.co/tech">
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<img src="https://sindresorhus.com/assets/thanks/standard-resume-logo.svg" width="180"/>
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</a>
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</p>
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</div>
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<br>
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<hr>
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</div>
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<br>
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<br>
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[](https://giphy.com/gifs/illustration-rainbow-unicorn-26AHG5KGFxSkUWw1i)
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[](https://www.npmjs.com/package/type-fest?activeTab=dependents) [](https://www.npmjs.com/package/type-fest)
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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).
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Either add this package as a dependency or copy-paste the needed types. No credit required. 👌
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PR welcome for additional commonly needed types and docs improvements. Read the [contributing guidelines](.github/contributing.md) first.
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## Install
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```
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$ npm install type-fest
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```
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*Requires TypeScript >=3.4*
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## Usage
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```ts
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import {Except} from 'type-fest';
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type Foo = {
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unicorn: string;
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rainbow: boolean;
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};
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type FooWithoutRainbow = Except<Foo, 'rainbow'>;
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//=> {unicorn: string}
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```
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## API
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Click the type names for complete docs.
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### Basic
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- [`Primitive`](source/basic.d.ts) - Matches any [primitive value](https://developer.mozilla.org/en-US/docs/Glossary/Primitive).
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- [`Class`](source/basic.d.ts) - Matches a [`class` constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes).
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- [`TypedArray`](source/typed-array.d.ts) - Matches any [typed array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), like `Uint8Array` or `Float64Array`.
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- [`JsonObject`](source/basic.d.ts) - Matches a JSON object.
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- [`JsonArray`](source/basic.d.ts) - Matches a JSON array.
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- [`JsonValue`](source/basic.d.ts) - Matches any valid JSON value.
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- [`ObservableLike`](source/basic.d.ts) - Matches a value that is like an [Observable](https://github.com/tc39/proposal-observable).
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### Utilities
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- [`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).
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- [`Mutable`](source/mutable.d.ts) - Create a type that strips `readonly` from all or some of an object's keys. The inverse of `Readonly<T>`.
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- [`Merge`](source/merge.d.ts) - Merge two types into a new type. Keys of the second type overrides keys of the first type.
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- [`MergeExclusive`](source/merge-exclusive.d.ts) - Create a type that has mutually exclusive keys.
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- [`RequireAtLeastOne`](source/require-at-least-one.d.ts) - Create a type that requires at least one of the given keys.
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- [`RequireExactlyOne`](source/require-exactly-one.d.ts) - Create a type that requires exactly a single key of the given keys and disallows more.
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- [`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.
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- [`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.
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- [`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).
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- [`Promisable`](source/promisable.d.ts) - Create a type that represents either the value or the value wrapped in `PromiseLike`.
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- [`Opaque`](source/opaque.d.ts) - Create an [opaque type](https://codemix.com/opaque-types-in-javascript/).
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- [`SetOptional`](source/set-optional.d.ts) - Create a type that makes the given keys optional.
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- [`SetRequired`](source/set-required.d.ts) - Create a type that makes the given keys required.
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- [`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.
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- [`PromiseValue`](source/promise-value.d.ts) - Returns the type that is wrapped inside a `Promise`.
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- [`AsyncReturnType`](source/async-return-type.d.ts) - Unwrap the return type of a function that returns a `Promise`.
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- [`ConditionalKeys`](source/conditional-keys.d.ts) - Extract keys from a shape where values extend the given `Condition` type.
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- [`ConditionalPick`](source/conditional-pick.d.ts) - Like `Pick` except it selects properties from a shape where the values extend the given `Condition` type.
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- [`ConditionalExcept`](source/conditional-except.d.ts) - Like `Omit` except it removes properties from a shape where the values extend the given `Condition` type.
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- [`UnionToIntersection`](source/union-to-intersection.d.ts) - Convert a union type to an intersection type.
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- [`Stringified`](source/stringified.d.ts) - Create a type with the keys of the given type changed to `string` type.
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- [`FixedLengthArray`](source/fixed-length-array.d.ts) - Create a type that represents an array of the given type and length.
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- [`IterableElement`](source/iterable-element.d.ts) - Get the element type of an `Iterable`/`AsyncIterable`. For example, an array or a generator.
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- [`Entry`](source/entry.d.ts) - Create a type that represents the type of an entry of a collection.
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- [`Entries`](source/entries.d.ts) - Create a type that represents the type of the entries of a collection.
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- [`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.
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- [`Asyncify`](source/asyncify.d.ts) - Create an async version of the given function type.
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### Template literal types
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*Note:* These require [TypeScript 4.1 or newer](https://devblogs.microsoft.com/typescript/announcing-typescript-4-1/#template-literal-types).
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- [`CamelCase`](ts41/camel-case.d.ts) – Convert a string literal to camel-case (`fooBar`).
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- [`KebabCase`](ts41/kebab-case.d.ts) – Convert a string literal to kebab-case (`foo-bar`).
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- [`PascalCase`](ts41/pascal-case.d.ts) – Converts a string literal to pascal-case (`FooBar`)
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- [`SnakeCase`](ts41/snake-case.d.ts) – Convert a string literal to snake-case (`foo_bar`).
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- [`DelimiterCase`](ts41/delimiter-case.d.ts) – Convert a string literal to a custom string delimiter casing.
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- [`Get`](ts41/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.
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### Miscellaneous
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- [`PackageJson`](source/package-json.d.ts) - Type for [npm's `package.json` file](https://docs.npmjs.com/creating-a-package-json-file).
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- [`TsConfigJson`](source/tsconfig-json.d.ts) - Type for [TypeScript's `tsconfig.json` file](https://www.typescriptlang.org/docs/handbook/tsconfig-json.html) (TypeScript 3.7).
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## Declined types
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*If we decline a type addition, we will make sure to document the better solution here.*
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- [`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.
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- [`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.
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- [`SubType`](https://github.com/sindresorhus/type-fest/issues/22) - The type is powerful, but lacks good use-cases and is prone to misuse.
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- [`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.
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## Tips
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### Built-in types
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There are many advanced types most users don't know about.
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- [`Partial<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1401-L1406) - Make all properties in `T` optional.
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<details>
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<summary>
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Example
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</summary>
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[Playground](https://www.typescriptlang.org/play/#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)
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```ts
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interface NodeConfig {
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appName: string;
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port: number;
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}
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class NodeAppBuilder {
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private configuration: NodeConfig = {
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appName: 'NodeApp',
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port: 3000
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};
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private updateConfig<Key extends keyof NodeConfig>(key: Key, value: NodeConfig[Key]) {
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this.configuration[key] = value;
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}
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config(config: Partial<NodeConfig>) {
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type NodeConfigKey = keyof NodeConfig;
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for (const key of Object.keys(config) as NodeConfigKey[]) {
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const updateValue = config[key];
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if (updateValue === undefined) {
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continue;
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}
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this.updateConfig(key, updateValue);
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}
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return this;
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}
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}
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// `Partial<NodeConfig>`` allows us to provide only a part of the
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// NodeConfig interface.
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new NodeAppBuilder().config({appName: 'ToDoApp'});
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```
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</details>
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- [`Required<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1408-L1413) - Make all properties in `T` required.
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<details>
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<summary>
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Example
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</summary>
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[Playground](https://typescript-play.js.org/?target=6#code/AQ4SwOwFwUwJwGYEMDGNgGED21VQGJZwC2wA3gFCjXAzFJgA2A-AFzADOUckA5gNxUaIYjA4ckvGG07c+g6gF8KQkAgCuEFFDA5O6gEbEwUbLm2ESwABQIixACJIoSdgCUYAR3Vg4MACYAPGYuFvYAfACU5Ko0APRxwADKMBD+wFAAFuh2Vv7OSBlYGdmc8ABu8LHKsRyGxqY4oQT21pTCIHQMjOwA5DAAHgACxAAOjDAAdChYxL0ANLHUouKSMH0AEmAAhJhY6ozpAJ77GTCMjMCiV0ToSAb7UJPPC9WRgrEJwAAqR6MwSRQPFGUFocDgRHYxnEfGAowh-zgUCOwF6KwkUl6tXqJhCeEsxDaS1AXSYfUGI3GUxmc0WSneQA)
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```ts
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interface ContactForm {
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email?: string;
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message?: string;
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}
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function submitContactForm(formData: Required<ContactForm>) {
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// Send the form data to the server.
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}
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submitContactForm({
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email: 'ex@mple.com',
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message: 'Hi! Could you tell me more about…',
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});
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// TypeScript error: missing property 'message'
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submitContactForm({
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email: 'ex@mple.com',
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});
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```
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</details>
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- [`Readonly<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1415-L1420) - Make all properties in `T` readonly.
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<details>
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<summary>
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Example
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</summary>
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[Playground](https://typescript-play.js.org/?target=6#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)
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```ts
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enum LogLevel {
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Off,
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Debug,
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Error,
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Fatal
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};
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interface LoggerConfig {
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name: string;
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level: LogLevel;
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}
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class Logger {
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config: Readonly<LoggerConfig>;
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constructor({name, level}: LoggerConfig) {
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this.config = {name, level};
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Object.freeze(this.config);
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}
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}
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const config: LoggerConfig = {
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name: 'MyApp',
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level: LogLevel.Debug
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};
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const logger = new Logger(config);
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// TypeScript Error: cannot assign to read-only property.
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logger.config.level = LogLevel.Error;
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// We are able to edit config variable as we please.
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config.level = LogLevel.Error;
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```
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</details>
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- [`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`.
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<details>
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<summary>
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Example
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</summary>
|
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[Playground](https://typescript-play.js.org/?target=6#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)
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|
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```ts
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interface Article {
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title: string;
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thumbnail: string;
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content: string;
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}
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// Creates new type out of the `Article` interface composed
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// from the Articles' two properties: `title` and `thumbnail`.
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// `ArticlePreview = {title: string; thumbnail: string}`
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type ArticlePreview = Pick<Article, 'title' | 'thumbnail'>;
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// Render a list of articles using only title and description.
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function renderArticlePreviews(previews: ArticlePreview[]): HTMLElement {
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const articles = document.createElement('div');
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for (const preview of previews) {
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// Append preview to the articles.
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}
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return articles;
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}
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const articles = renderArticlePreviews([
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{
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title: 'TypeScript tutorial!',
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thumbnail: '/assets/ts.jpg'
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}
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]);
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```
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</details>
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- [`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`.
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<details>
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<summary>
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Example
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</summary>
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|
||
[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#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-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 ${Constr.name} class`);
|
||
|
||
return instance;
|
||
}
|
||
|
||
|
||
const idleService = getInstance(IdleService);
|
||
// Will log: `Created 1 instances of IdleService class`
|
||
const newsEntry = getInstance(News, 'New ECMAScript proposals!', 'Last month...');
|
||
// Will log: `Created 1 instances of News class`
|
||
```
|
||
</details>
|
||
|
||
- [`Omit<T, K>`](https://github.com/microsoft/TypeScript/blob/71af02f7459dc812e85ac31365bfe23daf14b4e4/src/lib/es5.d.ts#L1446) – Constructs a type by picking all properties from T and then removing K.
|
||
<details>
|
||
<summary>
|
||
Example
|
||
</summary>
|
||
|
||
[Playground](https://typescript-play.js.org/?target=6#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-SgfXlHqVUE4xiAA)
|
||
|
||
```ts
|
||
interface Animal {
|
||
imageUrl: string;
|
||
species: string;
|
||
images: string[];
|
||
paragraphs: string[];
|
||
}
|
||
|
||
// Creates new type with all properties of the `Animal` interface
|
||
// except 'images' and 'paragraphs' properties. We can use this
|
||
// type to render small hover tooltip for a wiki entry list.
|
||
type AnimalShortInfo = Omit<Animal, 'images' | 'paragraphs'>;
|
||
|
||
function renderAnimalHoverInfo (animals: AnimalShortInfo[]): HTMLElement {
|
||
const container = document.createElement('div');
|
||
// Internal implementation.
|
||
return container;
|
||
}
|
||
```
|
||
</details>
|
||
|
||
- [`Uppercase<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms every character in a string into uppercase.
|
||
<details>
|
||
<summary>
|
||
Example
|
||
</summary>
|
||
|
||
```ts
|
||
type T = Uppercase<'hello'>; // 'HELLO'
|
||
|
||
type T2 = Uppercase<'foo' | 'bar'>; // 'FOO' | 'BAR'
|
||
|
||
type T3<S extends string> = Uppercase<`aB${S}`>;
|
||
type T4 = T30<'xYz'>; // 'ABXYZ'
|
||
|
||
type T5 = Uppercase<string>; // string
|
||
type T6 = Uppercase<any>; // any
|
||
type T7 = Uppercase<never>; // never
|
||
type T8 = Uppercase<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
||
```
|
||
</details>
|
||
|
||
- [`Lowercase<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms every character in a string into lowercase.
|
||
<details>
|
||
<summary>
|
||
Example
|
||
</summary>
|
||
|
||
```ts
|
||
type T = Lowercase<'HELLO'>; // 'hello'
|
||
|
||
type T2 = Lowercase<'FOO' | 'BAR'>; // 'foo' | 'bar'
|
||
|
||
type T3<S extends string> = Lowercase<`aB${S}`>;
|
||
type T4 = T32<'xYz'>; // 'abxyz'
|
||
|
||
type T5 = Lowercase<string>; // string
|
||
type T6 = Lowercase<any>; // any
|
||
type T7 = Lowercase<never>; // never
|
||
type T8 = Lowercase<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
||
```
|
||
</details>
|
||
|
||
- [`Capitalize<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms the first character in a string into uppercase.
|
||
<details>
|
||
<summary>
|
||
Example
|
||
</summary>
|
||
|
||
```ts
|
||
type T = Capitalize<'hello'>; // 'Hello'
|
||
|
||
type T2 = Capitalize<'foo' | 'bar'>; // 'Foo' | 'Bar'
|
||
|
||
type T3<S extends string> = Capitalize<`aB${S}`>;
|
||
type T4 = T32<'xYz'>; // 'ABxYz'
|
||
|
||
type T5 = Capitalize<string>; // string
|
||
type T6 = Capitalize<any>; // any
|
||
type T7 = Capitalize<never>; // never
|
||
type T8 = Capitalize<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
||
```
|
||
</details>
|
||
|
||
- [`Uncapitalize<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms the first character in a string into lowercase.
|
||
<details>
|
||
<summary>
|
||
Example
|
||
</summary>
|
||
|
||
```ts
|
||
type T = Uncapitalize<'Hello'>; // 'hello'
|
||
|
||
type T2 = Uncapitalize<'Foo' | 'Bar'>; // 'foo' | 'bar'
|
||
|
||
type T3<S extends string> = Uncapitalize<`AB${S}`>;
|
||
type T4 = T30<'xYz'>; // 'aBxYz'
|
||
|
||
type T5 = Uncapitalize<string>; // string
|
||
type T6 = Uncapitalize<any>; // any
|
||
type T7 = Uncapitalize<never>; // never
|
||
type T8 = Uncapitalize<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
||
```
|
||
</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)
|
||
- [Pelle Wessman](https://github.com/voxpelli)
|
||
|
||
## 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>
|