Interfaces in Object-Oriented Programming Languages and Prototype-Based Languages

What is an Interface in OOP

An interface is a programming structure used in many object-oriented languages (like Python, Java, and C#) that defines a set of methods and properties a class must implement, but without including the method bodies themselves.

Benefits of Using Interfaces:

• Abstraction: Interfaces allow us to hide implementation details and show only what’s necessary.
• Code consistency: All classes that implement the interface will follow the same structure.
• Polymorphism: Different classes can be used interchangeably if they implement the same interface
• Maintainability: Helps teams work more effectively by enforcing coding standards.
• Decoupling: Classes using interfaces are less dependent on specific implementations.

Why JavaScript Doesn’t Use Interfaces (By Default)

JavaScript is a prototype-based language, not a traditional OOP language. Until ES6, it didn’t even have class syntax, everything was built using functions and objects. Even today, under the hood, JavaScript still uses prototype based inheritance.

This design means that interfaces aren't built-in like they are in Python or Java. JavaScript doesn't enforce contracts between objects and methods. You can create an object and assign any property or method to it, there's no compiler checking to ensure it meets a defined structure.

JavaScript Object Creation Example:

How to Emulate Interfaces in JavaScript

JavaScript doesn't have built-in interfaces like languages such as Java or TypeScript. But interfaces are useful because they define a contract, a guarantee that certain methods and properties must exist on an object or class.

Even though JavaScript doesn’t enforce this by default, we can simulate interfaces in a few clever ways to bring structure and consistency to our code.

Here are the key ways to emulate interfaces in JavaScript, summarized in bullet points:

• Use comments/documentation to describe the expected methods and properties (soft contracts).
• Manually check for required methods using a custom function at runtime.
• Follow consistent naming conventions and structure using ES6 classes.
• Use JSDoc annotations with @interface and @implements for better tooling and IDE support.
• Adopt TypeScript, which adds real interface support and static type checking to JavaScript.

What is Strict Mode in JavaScript and Why Use It

Strict mode is a way to opt into a restricted version of JavaScript. It helps you catch bugs early and write cleaner code.

Why Use Strict Mode:

• Prevents usage of undeclared variables.
• Eliminates some silent JavaScript errors by throwing errors instead.
• Disallows usage of reserved keywords.
• Secures "this" keyword in functions.

What is TypeScript and How Does It Help with Interfaces

TypeScript is a superset of JavaScript developed by Microsoft. It adds static typing and other powerful features to JavaScript, such as interfaces, enums, and access modifiers.

Using TypeScript, we can define interfaces explicitly, just like we would in Java or Python, and the TypeScript compiler will enforce them.

It adds features like:

• Static typing (variables have defined types)
• Interfaces
• Classes with modifiers (public, private, etc.)
• Generics
• Better developer tooling (e.g., auto-complete, error checking)

TypeScript code is compiled into standard JavaScript so it can run in any browser or JavaScript environment

How TypeScript Enforces Strict Typing

TypeScript lets you declare variable and function types. The compiler then checks that your code follows those types, helping you catch bugs before runtime.

This prevents accidental type mismatches, which are common in plain JavaScript.