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TypeScript: Basics of the Type System

1. Introduction to TypeScript​

Developed by Microsoft, TypeScript is a superset of JavaScript. It provides a static type system, which is essential for large-scale application development.

  • Features: Static type checking, support for modern JS syntax, and deep integration with development tools (IDEs).
  • Advantages: Code auto-completion, ease of refactoring, and prevention of runtime errors.
  • Key Point: All valid JavaScript is also valid TypeScript (Substitutable).

2. Starting a Project​

The most common way to start is by using the tsc command.

# Global installation
npm install -g typescript

# Initialize project (creates tsconfig.json)
tsc --init

3. Core Syntax: Type Declarations​

// Basic type declarations
let name: string = "TypeScript User";
const age: number = 25;

// Interface
interface User {
    id: number;
    username: string;
    isAdmin: boolean;
}

const loginUser: User = {
    id: 1,
    username: "dev_user",
    isAdmin: true
};

// Function types
function add(a: number, b: number): number {
    return a + b;
}

4. Why Use TypeScript?​

By preventing errors like "undefined is not a function" during compile time, it significantly boosts productivity compared to JavaScript's dynamic typing nature.

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