Aura Dev

TypeScript Cheatsheet

TypeScript types, interfaces, and generics.

Basic Types

Primitives

let isDone: boolean = false;
let lines: number = 42;
let name: string = "Anders";

Arrays & Tuples

let list: number[] = [1, 2, 3];
let tuple: [string, number] = ["hello", 10];

Any, Void, Never

let notSure: any = 4;
function log(): void { console.log('hi'); }
function error(msg: string): never { throw new Error(msg); }

Interfaces & Types

Interfaces

interface User {
  id: number;
  name: string;
  age?: number; // Optional
  readonly role: string;
}

Type Aliases

type ID = string | number;
type Status = "pending" | "done" | "error";

Intersection Types

type Admin = User & { permissions: string[] };

Functions

Typing Functions

function add(x: number, y: number): number {
  return x + y;
}

const multiply = (x: number, y: number): number => x * y;

Function Overloads

function makeDate(timestamp: number): Date;
function makeDate(m: number, d: number, y: number): Date;
function makeDate(mOrTimestamp: number, d?: number, y?: number): Date {
  // implementation
}

Generics & Utility Types

Generics

function identity<T>(arg: T): T {
  return arg;
}

interface Box<T> {
  value: T;
}

Utility Types

type PartialUser = Partial<User>;
type ReadonlyUser = Readonly<User>;
type UserWithoutAge = Omit<User, 'age'>;
type UserKeys = keyof User;

What is TypeScript?

TypeScript is a strongly typed superset of JavaScript that adds static typing to catch errors at compile time.

This cheatsheet provides a quick reference for defining types, interfaces, generics, and utility types in TypeScript projects.

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