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JavaScript, TypeScript, Python, Java and C#: syntax, types, OOP, concurrency and idioms.

JavaScript

01Variables and Data Types 02Scope 03Hoisting 04Closures 05The this Keyword 06Prototypes 07Prototype Chain 08Classes 09Objects 10Arrays 11Functions 12Higher-Order Functions 13Callbacks 14Destructuring 15Spread and Rest Operators 16Modules (ES Modules) 17Error Handling 18Iterators and Generators 19Symbols 20Map 21Set 22WeakMap and WeakSet 23Hashing and Hash Tables 24Time and Space Complexity 25Synchronous vs Asynchronous Execution 26Call Stack 27Event Loop 28Microtasks vs Macrotasks 29Promises 30async / await 31Promise Chaining 32Error Handling in Asynchronous Code 33Parallel vs Sequential Async Operations 34Concurrency in JavaScript 35Cancellation / AbortController

TypeScript

01Type System Fundamentals 02Type Inference 03Interfaces 04Type Aliases 05Union Types 06Intersection Types 07Generics 08Enums 09Utility Types 10Conditional Types 11Mapped Types 12Type Guards and Narrowing 13keyof and typeof Operators 14The infer Keyword 15Generic Constraints 16any vs unknown vs never 17Declaration Files 18TypeScript Configuration (tsconfig.json)

Python

01Syntax and Data Types 02Variables and Scope 03Functions and *args / **kwargs 04Data Structures 05Comprehensions 06OOP: Classes and Objects 07Inheritance and Polymorphism 08Decorators 09Generators and Iterators 10Exception Handling 11Modules and Packages 12Context Managers 13Type Hints 14Asyncio Basics 15The GIL and Choosing a Concurrency Model 16Python's Memory Model and Garbage Collection 17Dataclasses, Pydantic and Data Validation 18FastAPI Essentials 19Packaging, Dependencies and Environments 20Python Performance and Profiling

Java

01Syntax and Data Types 02OOP Fundamentals 03Inheritance and Polymorphism 04Collections Framework 05Exception Handling 06Generics 07Streams and Lambdas 08Concurrency Basics

C#

01C# Syntax and Data Types 02C# OOP Fundamentals 03LINQ (Language Integrated Query) 04Collections and Generics 05Exception Handling 06Async/Await 07.NET Project Structure 08Delegates and Events 09The CLR and Garbage Collection 10Value Types, Span<T> and Memory<T> 11Async Internals, ValueTask and Cancellation 12Threading, the TPL and Synchronization 13The ASP.NET Core Request Pipeline and Middleware 14Dependency Injection Lifetimes in .NET 15EF Core in Depth 16Modern C#: Records, Pattern Matching and Nullable Reference Types 17Performance and Benchmarking in .NET 18.NET Interview Gotchas