TypeScript Methods and Features Reference

This project provides a comprehensive overview of commonly used TypeScript methods and features, grouped by their functionality, along with brief descriptions and usage examples.

Basic Types

TypeScript Type	Description	Example
boolean	Represents true/false values	let isDone: boolean = false;
number	Represents numeric values	let decimal: number = 6;
string	Represents text values	let color: string = "blue";
array	Represents an array of values	let list: number[] = [1, 2, 3];
tuple	Represents an array with fixed number of elements of specific types	let x: [string, number]; x = ["hello", 10];
enum	Represents a collection of related values	enum Color {Red, Green, Blue}; let c: Color = Color.Green;
any	Represents any type	let notSure: any = 4; notSure = "maybe a string instead";
void	Represents the absence of a type	function warnUser(): void { console.log("This is my warning message"); }
null and undefined	Represents null and undefined values	let u: undefined = undefined; let n: null = null;

Interfaces

TypeScript Feature	Description	Example
interface	Defines a contract for objects	interface LabeledValue { label: string; } function printLabel(labeledObj: LabeledValue) { console.log(labeledObj.label); }
Optional Properties	Properties that are optional in interfaces	interface SquareConfig { color?: string; width?: number; }
Readonly Properties	Properties that cannot be modified	interface Point { readonly x: number; readonly y: number; }

Functions

TypeScript Feature	Description	Example
Function Types	Defines types for functions	let myAdd: (x: number, y: number) => number = function(x: number, y: number): number { return x + y; };
Optional Parameters	Parameters that are optional in functions	function buildName(firstName: string, lastName?: string) { if (lastName) return firstName + " " + lastName; else return firstName; }
Default Parameters	Parameters with default values	function buildName(firstName: string, lastName = "Smith") { return firstName + " " + lastName; }

Classes

TypeScript Feature	Description	Example
class	Defines a class	class Greeter { greeting: string; constructor(message: string) { this.greeting = message; } greet() { return "Hello, " + this.greeting; } }
Inheritance	Classes can inherit from other classes	class Animal { move(distanceInMeters: number = 0) { console.log(\Animal moved ${distanceInMeters}m.`); } } class Dog extends Animal { bark() { console.log('Woof! Woof!'); } }`
super	Calls the constructor of the base class	class Dog extends Animal { constructor(name: string) { super(name); } }
Public, Private, and Protected Modifiers	Access control keywords for class members	class Animal { private name: string; public constructor(theName: string) { this.name = theName; } }

Modules

TypeScript Feature	Description	Example
export	Exports a member from a module	export class ZipCodeValidator { isAcceptable(s: string) { return s.length === 5 && numberRegexp.test(s); } }
import	Imports a member from a module	import { ZipCodeValidator } from "./ZipCodeValidator";

Generics

TypeScript Feature	Description	Example
Generics	Enables creating components that work with any data type	function identity<T>(arg: T): T { return arg; } let output = identity<string>("myString");

Utility Types

TypeScript Utility Type	Description	Example
Partial	Constructs a type with all properties set to optional	interface Todo { title: string; description: string; } function updateTodo (todo: Todo, fieldsToUpdate: Partial<Todo>) { return { ...todo, ...fieldsToUpdate }; }
Readonly	Constructs a type with all properties set to readonly	interface Todo { title: string; } const todo: Readonly<Todo> = { title: "Delete inactive users" };

Type Assertions

TypeScript Feature	Description	Example
as syntax	Tells the compiler to treat an entity as a different type	let someValue: any = "this is a string"; let strLength: number = (someValue as string).length;

Type Guards

TypeScript Feature	Description	Example
typeof	Type guard for primitive types	`function padLeft(value: string, padding: string
instanceof	Type guard for class types	if (pet instanceof Dog) { pet.bark(); }

Advanced Types

TypeScript Feature	Description	Example
Intersection Types	Combines multiple types into one	interface ErrorHandling { success: boolean; error?: { message: string; } } interface ArtworksData { artworks: { title: string; }[] } type ArtworksResponse = ErrorHandling & ArtworksData;
Union Types	A value can be one of several types	`function printId(id: number

This document provides a quick reference to commonly used TypeScript methods and features. For more detailed information, refer to the TypeScript Handbook.