Introduction to TypeScript

• TypeScript is a syntactic superset of JavaScript.
• Adds static typing to prevent common coding mistakes.
• Catches errors during development that JavaScript wouldn't.
• Acts like a buddy to double-check your work.

Setting Up TypeScript

1. Installation

   • Run in terminal: npm install typescript --save-dev

2. Initialize Configuration

   • Command: npx tsc --init

3. TS Config File

   • Contains various compiler options.
   • Compiler Options:
     • Target: Selects JavaScript version (e.g., ES2020).
     • Module: Default is CommonJS; can use ES6 or ESNext.
     • ES Module Interop: Smoothes compatibility issues.
     • Force Consistent Casing in File Names: Ensures case sensitivity.
     • Strict: Enables strict type-checking.
     • Skip Lib Check: Skips type-checking for library files.

Basic TypeScript Usage

Variable Types

• String Variable Example:

  • For user registration, declare: let name: string = 'John Doe';
  • TypeScript catches errors if non-string values are assigned.

• Number Variable Example:

  • For discounts: let discount: number;
  • Ensures only numbers are accepted, preventing revenue loss.

• Boolean Variable Example:

  • Feature toggle for beta users: let isBetaUser: boolean;

Arrays

• String Array Example:

  • Use let topSellers: string[]; to restrict array values.

• Union Type for Arrays:

  • let topSellers: (string | number)[];
  • Allows both strings and numbers in the array.

Functions

• Function Example: Loan Calculation
  • Function signature: function calculateLoan(amount: number, rate: number): number {}
  • TypeScript ensures both inputs and output are numbers.

Working with Objects

• Interfaces:

  • Define structure of objects (e.g., employee data).
  • Example: interface Employee { id: number; name: string; position?: string; // Optional property }
  • Ensures consistency in object structure.

• Type Aliases:

  • Create custom types for clarity (e.g., type Username = string;).
  • Can restrict to specific values using literal types (e.g., type Role = 'admin' | 'user';).

Enums

• Enums in TypeScript:
  • Define named constant values (e.g., Subscription tiers).
  • Example: enum Subscription { Free, Basic, Premium }
  • Improves readability and reduces errors.

Generics

• Generics Overview:
  • Create reusable components that work with multiple data types.
  • Example: function identity<T>(arg: T): T { return arg; }
  • Ensures type safety by making types consistent between input and output.

Conclusion

• This is just the basics of TypeScript.
• Advanced features will be covered in future videos.
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