What is the "extends" keyword in a Spider?

The keyword extends

allows you to inherit from an existing object. For example, suppose you have an object Animal

:

fn Animal(name) {
  this.name = name;

  this.walk = fn() {
    console.log('\(name) is walking...');
  };
}

Animal.prototype.getLegs = fn() {
  return 4;
};

      

        
        
        
      

    

Now you can create another object that inherits Animal

using the extends keyword:

fn Spider(name)
  extends Animal(name) {

}

Spider.prototype.getLegs = fn() {
  return 8;
};

      

        
        
        
      

    

When you create a new object Spider

, you will automatically get your method walk

, because Spider

extends Animal

.

var spider = new Spider("Skitter the Spider");
spider.walk();

      

        
        
        
      

    

The spider (language) also provides a keyword super

that allows you to easily access the object you are distributing. For example:

Spider.prototype.getLegs = fn() {
  return super.getLegs() + 4; 
};

spider.getLegs(); // => 8

      

        
        
        
      

    

Implementation

This code in Spider:

fn Spider() extends Animal {}

      

        
        
        
      

    

the following JavaScript is compiled:

function Spider() {
  Animal.call(this);
}

Spider.prototype = Object.create(Animal);