sfcode
An Online Competing and Development Environment
|
Example
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.
Requires TypeScript >=3.2
Click the type names for complete docs.
Primitive
- Matches any primitive value.Class
- Matches a class
constructor.TypedArray
- Matches any typed array, like Uint8Array
or Float64Array
.JsonObject
- Matches a JSON object.JsonArray
- Matches a JSON array.JsonValue
- Matches any valid JSON value.ObservableLike
- Matches a value that is like an Observable.Except
- Create a type from an object type without certain keys. This is a stricter version of Omit
.Mutable
- Convert an object with readonly
keys into a mutable object. The inverse of Readonly<T>
.Merge
- Merge two types into a new type. Keys of the second type overrides keys of the first type.MergeExclusive
- Create a type that has mutually exclusive keys.RequireAtLeastOne
- Create a type that requires at least one of the given keys.RequireExactlyOne
- Create a type that requires exactly a single key of the given keys and disallows more.PartialDeep
- Create a deeply optional version of another type. Use Partial<T>
if you only need one level deep.ReadonlyDeep
- Create a deeply immutable version of an object
/Map
/Set
/Array
type. Use Readonly<T>
if you only need one level deep.LiteralUnion
- 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.Promisable
- Create a type that represents either the value or the value wrapped in PromiseLike
.Opaque
- Create an opaque type.SetOptional
- Create a type that makes the given keys optional.SetRequired
- Create a type that makes the given keys required.PromiseValue
- Returns the type that is wrapped inside a Promise
.AsyncReturnType
- Unwrap the return type of a function that returns a Promise
.ConditionalKeys
- Extract keys from a shape where values extend the given Condition
type.ConditionalPick
- Like Pick
except it selects properties from a shape where the values extend the given Condition
type.ConditionalExcept
- Like Omit
except it removes properties from a shape where the values extend the given Condition
type.PackageJson
- Type for npm's package.json
file.TsConfigJson
- Type for TypeScript's tsconfig.json
file (TypeScript 3.7).If we decline a type addition, we will make sure to document the better solution here.
Diff
and Spread
- 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
- You only save a few characters (Dictionary<number>
vs Record<string, number>
) from Record
, which is more flexible and well-known. Also, you shouldn't use an object as a dictionary. We have Map
in JavaScript now.There are many advanced types most users don't know about.
Partial<T>
- Make all properties in T
optional. <details>```ts interface NodeConfig { appName: string; port: number; }
class NodeAppBuilder { private configuration: NodeConfig = { appName: 'NodeApp', port: 3000 };
private updateConfig<Key extends keyof NodeConfig>(key: Key, value: NodeConfig[Key]) { this.configuration[key] = value; }
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.updateConfig(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>
- Make all properties in T
required. <details>Example
```ts interface ContactForm { email?: string; message?: string; }
function submitContactForm(formData: Required<ContactForm>) { // Send the form data to the server. }
submitContactForm({ email: 'ex@mp', message: 'Hi! Could you tell me more about…', }); le.c om
// TypeScript error: missing property 'message' submitContactForm({ email: 'ex@mp', }); ``` </details> le.c om
Readonly<T>
- Make all properties in T
readonly. <details>Example
```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>
- From T
, pick a set of properties whose keys are in the union K
. <details>Example
```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>
- Construct a type with a set of properties K
of type T
. <details>Example
```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>
- Exclude from T
those types that are assignable to U
. <details>Example
```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>
- Extract from T
those types that are assignable to U
. <details>Example
```ts declare function uniqueId(): number;
const ID = Symbol('ID');
interface Person {
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 = {
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>
- Exclude null
and undefined
from T
. <details>Example
Works with
set to
. (Read more here)
```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>
- Obtain the parameters of a function type in a tuple. <details>Example
```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>
- Obtain the parameters of a constructor function type in a tuple. <details>Example
```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>
– Obtain the return type of a function type. <details>Example
``ts /** Provides every element of the iterable
iterinto 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>
– Obtain the instance type of a constructor function type. <details>Example
```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>
– Constructs a type by picking all properties from T and then removing K. <details>Example
```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.
(MIT OR CC0-1.0)