Welcome to OOP Interview Prep

This course covers the OOP concepts interviewers actually probe on: the four pillars, encapsulation and access modifiers, abstraction with abstract classes and interfaces, inheritance deep-dives, polymorphism through overloading and overriding, object relationships, SOLID principles, and foundational design patterns.

What You'll Learn

• OOP Fundamentals - What OOP is, classes vs objects, the four pillars, this, object lifecycle
• Encapsulation - Access modifiers, private fields in JS, getters and setters
• Abstraction - Abstract classes, interfaces, abstraction patterns in JavaScript
• Inheritance - Single, multilevel, multiple inheritance, the diamond problem, super
• Polymorphism - Method overriding, overloading simulation in JS, constructor overloading
• Object Relationships - Association, aggregation, composition and when to use each
• SOLID Principles - SRP, OCP, LSP, ISP, DIP with before/after refactoring examples
• Design Patterns - Singleton, Factory, Builder, Strategy, State patterns

How to Use This Course

Work through the chapters in order. Each lesson starts with a short hook, shows the concept with runnable JavaScript code, and ends with interview questions and a cheat sheet. Use the sidebar to jump around once you know the shape.

Prerequisites

• Basic JavaScript (functions, variables, arrays)
• Familiarity with ES6+ syntax (classes, arrow functions, destructuring)
• No prior OOP knowledge required

Let's get started with the fundamentals.