How to implement polymorphism in JavaScript

JavaScript is a dynamic, object-oriented programming language that supports polymorphism. Polymorphism means that the same method can exhibit different behaviors in different situations, which is of great significance to the flexibility and scalability of the program. In this article, we will explore how polymorphism is implemented in JavaScript.

Polymorphism in JavaScript is achieved based on its object-oriented features. Object-oriented programming in JavaScript is mainly implemented through objects and prototypes. We implement polymorphism in the following two ways.

1. Using inheritance

In JavaScript, one object can inherit the properties and methods of another object. Inheritance provides a way to achieve polymorphism. We can define methods with the same name in subclasses and parent classes, and provide different implementations for this method in different situations. The implementation of the parent class can be called through the super keyword.

The following is a simple example:

class Animal {
  speak() {
    console.log('Animal is speaking.')
  }
}

class Dog extends Animal {
  speak() {
    console.log('Woof!')
  }
}

class Cat extends Animal {
  speak() {
    console.log('Meow!')
  }
}

let animal = new Animal()
let dog = new Dog()
let cat = new Cat()

animal.speak() // 输出 "Animal is speaking."
dog.speak() // 输出 "Woof!"
cat.speak() // 输出 "Meow!"

In the above example, we created a parent class Animal and two subclasses Dog and Cat. They all override the speak() method and implement different behaviors in different situations. When we call this method, the output results are also different.

2. Using interfaces

There is no special concept of interface in JavaScript, but we can realize the concept of interface by defining a set of methods that need to be implemented. If an object implements this set of methods, we can consider it to implement this interface.

The following is an example:

class Shape {
  draw() {
    console.log('Shape is drawing.')
  }
}

class Circle extends Shape {
  draw() {
    console.log('Circle is drawing.')
  }
}

class Rectangle extends Shape {
  draw() {
    console.log('Rectangle is drawing.')
  }
}

let circle = new Circle()
let rectangle = new Rectangle()

function drawShape(shape) {
  if (shape.draw instanceof Function) {
    shape.draw()
  }
}

drawShape(circle) // 输出 "Circle is drawing."
drawShape(rectangle) // 输出 "Rectangle is drawing."

In the above example, we created a parent class Shape and two subclasses Circle and Rectangle. They all implement the draw() method. Then we define a function drawShape(), which receives a parameter shape, and when the shape implements the draw() method, we call it.

Conclusion

The above are two ways to achieve polymorphism in JavaScript. We can reflect polymorphism through inheritance and interfaces, thereby improving the flexibility and scalability of the program. In actual development, we can choose the appropriate way to implement polymorphism according to the specific situation.

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