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Mastering TypeScript

Classes and Interfaces

Learn about the relationship between classes and interfaces in object-oriented design patterns.

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Relationship between classes and interfaces

There is a very strong relationship between classes and interfaces, particularly in object-oriented design patterns. An interface describes a custom type and can include both properties and functions. A class is the definition of an object, also including its properties and functions. This allows us to use interfaces to describe some common behavior within a set of classes and write code that will work with this set of classes.

As an example of this, consider the following class definitions:

TypeScript 4.9.5
// Define a class ClassA with a method print
class ClassA {
  // Method print with a void return type
  print(): void {
    // Log message indicating that ClassA.print has been called
    console.log(`ClassA.print() called.`)
  };
}
// Define a class ClassB with a method print
class ClassB {
  // Method print with a void return type
  print(): void {
    // Log message indicating that ClassB.print has been called
    console.log(`ClassB.print() called.`)
  };
}
Class definitions

Here, we have class definitions for two classes, named ClassA (lines 2–8) and ClassB (lines 11–17). Both of these ...