TypeScript-cheatsheet
Een doorzoekbaar, afdrukbaar TypeScript-naslagwerk: types, interfaces, generics, utility types, narrowing, declaratiebestanden en tsconfig. Gratis.
Basic types
14let name: string = "Ada";
String type annotation
let age: number = 30;
Number (int and float)
let ok: boolean = true;
Boolean
let ids: number[] = [1, 2];
Array of numbers
let pair: [string, number] = ["a", 1];
Tuple: fixed-length typed array
let anything: unknown;
Safe any: must narrow before use
let loose: any;
Opts out of checking (avoid)
function log(): void {}
No return value
function fail(): never { throw new Error(); }
Never returns
let big: bigint = 9007199254740993n;
Arbitrary-precision integer
let id: string | null = null;
Nullable via union
const point = { x: 1 } as const;
Deep readonly literal types
enum Status { Active, Inactive }
Numeric enum
type Dir = "up" | "down";
String literal union (enum-lite)
Interfaces & type aliases
12interface User { id: number; name: string; }
Object shape contract
type User = { id: number; name: string };
Type alias for a shape
interface User { nickname?: string; }
Optional property
interface User { readonly id: number; }
Property cannot be reassigned
interface Admin extends User { role: string; }
Interface inheritance
type Admin = User & { role: string };
Extend an alias via intersection
interface Dict { [key: string]: number; }
Index signature
interface Fn { (x: number): string; }
Callable interface
interface User { greet(): void; }
Method signature
interface Box<T> { value: T; }
Generic interface
interface Window { myGlobal: string; }
Declaration merging (augment)
type Point = Readonly<{ x: number }>;
Readonly wrapper on an alias
Unions, intersections & narrowing
12type Id = string | number;
Union: one of several types
type Full = A & B;
Intersection: all members of both
if (typeof id === "string") { ... }
typeof narrowing
if (el instanceof HTMLElement) { ... }
instanceof narrowing
if ("radius" in shape) { ... }
in-operator narrowing
if (value != null) { ... }
Strip null AND undefined
switch (shape.kind) { case "circle": ... }
Discriminated union switch
type Shape = Circle | Square;
Discriminated union (kind field)
const x = cond ? a : b;
Result type is a union of both
user?.address?.city
Optional chaining
const name = input ?? "default";
Nullish coalescing
function assertNever(x: never): never { throw x; }
Exhaustiveness check helper
Generics
11function first<T>(arr: T[]): T { return arr[0]; }
Generic function
first<string>(["a", "b"])
Explicit type argument
interface Box<T> { value: T; }
Generic interface
class Stack<T> { items: T[] = []; }
Generic class
type Pair<K, V> = { key: K; value: V };
Generic type alias
<T extends { id: number }>
Constrain the type parameter
<T, K extends keyof T>(obj: T, key: K): T[K]
Typed property access
<T = string>
Default type parameter
function wrap<const T>(v: T): T[]
const modifier keeps literals
type Flatten<T> = T extends Array<infer U> ? U : T;
Extract inner type with infer
const map = new Map<string, User>();
Generic built-in collections
Utility types
14Partial<User>
All properties optional
Required<User>
All properties required
Readonly<User>
All properties readonly
Pick<User, "id" | "name">
Keep only the listed keys
Omit<User, "password">
Drop the listed keys
Record<string, number>
Object map of key to value type
Exclude<T, U>
Remove U members from union T
Extract<T, U>
Keep only U members of union T
NonNullable<T>
Strip null and undefined
ReturnType<typeof fn>
Type a function returns
Parameters<typeof fn>
Tuple of a function's params
Awaited<Promise<string>>
Unwrap promise type → string
InstanceType<typeof MyClass>
Instance type from a class
Uppercase<"id"> / Capitalize<"id">
String-literal case transforms
Functions & overloads
11function add(a: number, b: number): number
Typed parameters and return
const add = (a: number, b: number) => a + b;
Arrow function (return inferred)
function log(msg: string, level?: string)
Optional parameter
function log(msg: string, level = "info")
Default parameter value
function sum(...nums: number[]): number
Rest parameters
type Handler = (e: Event) => void;
Function type alias
function get(id: number): User;
function get(ids: number[]): User[];
function get(x: any): any { ... }
Overload signatures + one impl
function fn(this: HTMLElement, e: Event)
Typed this parameter
async function load(): Promise<User>
Async returns a Promise
function isUser(x: unknown): x is User
Type predicate return
const fn: typeof otherFn = ...;
Reuse another function's type
Classes
12class User { constructor(public name: string) {} }
Parameter property shorthand
private secret: string;
Compile-time private member
#secret: string;
Runtime private field (ES)
protected id: number;
Visible to subclasses only
readonly createdAt = new Date();
Assign once, in ctor only
static create(): User { return new User(); }
Static factory method
class Admin extends User { ... }
Inheritance (use super())
class Api implements Fetcher { ... }
Implement an interface
abstract class Shape { abstract area(): number; }
Abstract base class
get fullName(): string { return ...; }
Getter accessor
override toString(): string { ... }
Explicit override (safer)
declare id: number;
Declare without initializing
Type guards & assertions
11function isUser(x: unknown): x is User
Custom type guard
function assertUser(x: unknown): asserts x is User
Assertion function
function assertOk(x: unknown): asserts x
Assert truthy (non-null after)
const el = input as HTMLInputElement;
Type assertion (cast)
value!
Non-null assertion (careful!)
x as unknown as Y
Double assertion (last resort)
const roles = ["admin", "user"] as const;
Literal tuple via const assert
if (Array.isArray(value)) { ... }
Built-in array guard
satisfies Record<string, string>
Check shape, keep inference
typeof x === "object" && x !== null
Safe object check (null trap)
catch (e) { if (e instanceof Error) ... }
Narrow the unknown catch var
Mapped & conditional types
12type Flags<T> = { [K in keyof T]: boolean };
Mapped type over keys
{ [K in keyof T]?: T[K] }
Add ? modifier (Partial)
{ [K in keyof T]-?: T[K] }
Remove ? modifier (Required)
{ readonly [K in keyof T]: T[K] }
Add readonly to all keys
{ -readonly [K in keyof T]: T[K] }
Strip readonly (Mutable)
{ [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K] }
Key remapping with as
type IsString<T> = T extends string ? true : false;
Conditional type
T extends (infer U)[] ? U : never
infer inside a conditional
type Keys = keyof User;
Union of property names
type Value = User["name"];
Indexed access type
type Route = `/users/${number}`;
Template literal type
T extends any ? T[] : never
Distribute over union members
Modules & declaration files
12export interface User { ... }
Named export
export default class Api { ... }
Default export
import { User } from "./user";
Named import
import type { User } from "./user";
Type-only import (erased)
export type { User };
Type-only re-export
import * as path from "node:path";
Namespace import
declare module "my-lib" { ... }
Type an untyped package
declare global { interface Window { ... } }
Augment global scope
declare const VERSION: string;
Ambient declaration (.d.ts)
export {};
Force a file to be a module
/// <reference types="node" />
Triple-slash type reference
npm i -D @types/lodash
Install community typings
tsconfig essentials
13"strict": true
Enable all strict checks (do it)
"target": "ES2022"
Output JavaScript version
"module": "ESNext"
Emitted module system
"moduleResolution": "bundler"
Resolution for Vite/esbuild
"noEmit": true
Type-check only, no output
"esModuleInterop": true
Smooth CommonJS default imports
"skipLibCheck": true
Skip checking .d.ts files
"noUncheckedIndexedAccess": true
arr[i] becomes T | undefined
"paths": { "@/*": ["./src/*"] }
Import path aliases
"outDir": "./dist", "rootDir": "./src"
Output / source directories
"sourceMap": true, "declaration": true
Emit .map and .d.ts files
npx tsc --noEmit
CI type-check command
npx tsc --init
Generate a tsconfig.json
Geen vermelding komt overeen met “:q”.
Over TypeScript-cheatsheet
Deze TypeScript cheat sheet zet het typesysteem om in één doorzoekbare pagina: basistypes, interfaces en type aliases, unions, intersections en narrowing, generics, de ingebouwde utility types, functies en overloads, klassen, type guards en assertions, mapped en conditional types, modules en declaratiebestanden, en de tsconfig-opties die er echt toe doen.
Hij is geschreven voor dagelijks werk: de exacte vorm van een generic constraint, wat Pick, Omit, Record en ReturnType doen, hoe een discriminated union versmalt, wanneer je naar `satisfies` moet grijpen in plaats van een cast, zodat u een detail kunt controleren zonder uw editor te verlaten voor de handleiding.
Zoals elke cheat sheet in deze groep is hij gratis en client-side: filter rijen live met de zoekbalk, spring tussen secties met de plakkende inhoudsopgave, kopieer elke code met één klik en druk de pagina af als referentie op uw bureau.
Hoe gebruik je TypeScript-cheatsheet
- Open de sheet en blader door de secties, van Basistypes en Generics tot tsconfig-essentials.
- Zoek op een trefwoord zoals Partial, narrowing of satisfies om elke rij live te filteren.
- Ga naar Utility types of Mapped & conditional types wanneer u de geavanceerde type-syntax nodig heeft.
- Klik op een codefragment of het kopieerpictogram om de TypeScript naar uw klembord te kopiëren.
- Gebruik Afdrukken voor een papieren exemplaar van de volledige TypeScript-referentie.
Veelgestelde vragen
Elf secties: basistypes, interfaces en type aliases, unions en narrowing, generics, utility types, functies en overloads, klassen, type guards en assertions, mapped en conditional types, modules en declaratiebestanden, en tsconfig-essentials.
Ja. Een aparte sectie behandelt Partial, Required, Readonly, Pick, Omit, Record, Exclude, Extract, ReturnType, Awaited en de rest, elk met een uitleg van één regel.
Zeer. Aparte secties tonen typeof- en instanceof-narrowing, discriminated unions, door de gebruiker gedefinieerde type predicates, assertion functions en het verschil tussen een cast en `satisfies`.
Ja. Klik op de code op elke rij of het kopieerpictogram en het wordt direct naar uw klembord gekopieerd.
Ja, volledig gratis en draait in uw browser zonder in te loggen.
Populaire zoekopdrachten
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tsconfig options
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