Add Comprehensive TypeScript Cheatsheet with Intro and Installation Guide

languages/typescript.sh

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+# *****************************************************************************
+# Introduction to TypeScript
+# *****************************************************************************
+
+# What is TypeScript?
+# TypeScript is a strongly typed programming language that builds on JavaScript, giving you better tooling at any scale.
+# It's a superset of JavaScript, which means all JavaScript code is valid TypeScript, but TypeScript has additional features like static typing, interfaces, and generics.
+
+# Why Use TypeScript?
+# - Provides type safety on top of the JavaScript, reducing runtime errors.
+# - Makes the code more readable and maintainable.
+# - Offers great tooling support with IntelliSense in popular editors.
+# - Facilitates easier refactoring and debugging.
+
+# *****************************************************************************
+# Installing TypeScript
+# *****************************************************************************
+
+# Prerequisites:
+# - Ensure Node.js is installed on your system. If not, download and install it from https://nodejs.org/
+
+# Installation:
+# - TypeScript can be installed as a Node.js package globally or in your project using npm (Node Package Manager).
+# - To install TypeScript globally, use the following command in your terminal:
+npm install -g typescript
+
+# Checking Installation:
+# - To verify that TypeScript has been installed correctly, you can check its version:
+tsc --version
+
+# Compiling TypeScript to JavaScript:
+# - Once installed, you can compile .ts files to .js using the TypeScript compiler. For example:
+tsc hello.ts
+
+# *****************************************************************************
+# Basic Syntax and Data Types
+# *****************************************************************************
+
+// Boolean type
+let isDone: boolean = false;
+
+// Number type
+let decimal: number = 6;
+
+// String type
+let color: string = "blue";
+
+// Array type
+let list: number[] = [1, 2, 3];
+
+// Tuple type
+let tuple: [string, number] = ["hello", 10];
+
+// Enum type
+enum Color { Red, Green, Blue }
+
+// Any type
+let notSure: any = 4;
+
+// Void type
+let unusable: void = undefined;
+
+// Null and Undefined
+let u: undefined = undefined;
+let n: null = null;
+
+# *****************************************************************************
+# Functions
+# *****************************************************************************
+
+// Function with no return type
+function warnUser(): void { /* ... */ }
+
+// Function with return type
+function buildName(firstName: string, lastName: string): string { /* ... */ }
+
+// Function with optional parameters
+function buildNameOptional(firstName: string, lastName?: string): string { /* ... */ }
+
+// Function with default parameters
+function buildNameDefault(firstName: string, lastName = "Smith"): string { /* ... */ }
+
+# *****************************************************************************
+# Interfaces
+# *****************************************************************************
+
+// Simple interface
+interface LabelledValue {
+ label: string;
+}
+
+// Function in an interface
+interface SearchFunc {
+ (source: string, subString: string): boolean;
+}
+
+// Indexable types
+interface StringArray {
+ [index: number]: string;
+}
+
+// Class types in interfaces
+interface ClockInterface {
+ currentTime: Date;
+ setTime(d: Date): void;
+}
+
+# *****************************************************************************
+# Classes
+# *****************************************************************************
+
+// Basic class
+class Greeter {
+ greeting: string;
+ constructor(message: string) { this.greeting = message; }
+ greet() { return "Hello, " + this.greeting; }
+}
+
+// Inheritance
+class Animal {
+ move(distanceInMeters: number = 0) { /* ... */ }
+}
+class Dog extends Animal {
+ bark() { /* ... */ }
+}
+
+// Class with interfaces
+class Clock implements ClockInterface {
+ currentTime: Date = new Date();
+ setTime(d: Date) { this.currentTime = d; }
+}
+
+# *****************************************************************************
+# Advanced Types
+# *****************************************************************************
+
+// Union types
+function padLeft(value: string, padding: string | number) { /* ... */ }
+
+// Intersection types
+interface BusinessPartner {
+ name: string;
+ credit: number;
+}
+type Contact = BusinessPartner & { email: string };
+
+// Type guards
+function isFish(pet: Fish | Bird): pet is Fish { /* ... */ }
+
+// Nullable types
+function f(sn: string | null): string { /* ... */ }
+
+// Type Aliases
+type NameOrNameArray = string | string[];
+
+// Generics
+function identity<T>(arg: T): T { return arg; }
+
+# *****************************************************************************
+# Enums and Namespaces
+# *****************************************************************************
+
+// Numeric enums
+enum Direction { Up = 1, Down, Left, Right }
+
+// String enums
+enum Response { No = "NO", Yes = "YES" }
+
+// Namespaces
+namespace Validation {
+ export interface StringValidator {
+ isAcceptable(s: string): boolean;
+ }
+}
+
+# *****************************************************************************
+# Modules
+# *****************************************************************************
+
+// Importing modules
+import { moduleName } from "module";
+
+// Exporting from modules
+export function someFunction() { /* ... */ }
+
+// Default exports
+export default class SomeType { /* ... */ }
+
+# *****************************************************************************
+# Decorators
+# *****************************************************************************
+
+// Class decorator
+function sealed(constructor: Function) { /* ... */ }
+
+// Method decorator
+function enumerable(value: boolean) {
+ return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) { /* ... */ };
+}
+
+// Accessor decorator
+function configurable(value: boolean) { /* ... */ }
+
+# *****************************************************************************
+# Type Assertions
+# *****************************************************************************
+
+let someValue: any = "this is a string";
+let strLength: number = (someValue as string).length;
+
+# *****************************************************************************
+# Miscellaneous
+# *****************************************************************************
+
+// Type inference
+let x = 3; // `x` will be inferred as `number`
+
+// Type compatibility
+interface Named {
+ name: string;
+}
+let x: Named;
+let y = { name: "Alice", location: "Seattle" };
+x = y; // OK
+
+// Ambient declarations
+declare var $: JQuery;