JavaScript Prototype

 Let me explain the varied way of making objects in JavaScript. one among the ways to make objects in JavaScript is that the constructor function. Consider the below constructor function:

function Bike(model,color){
   this.model = model,
   this.color = color,this.getDetails = function(){
     return this.model+' bike is '+this.color;
   }
}
var bikeObj1 = new Bike('BMW','BLACK');
var bikeObj2 = new Bike('BMW','WHITE');console.log(bikeObj1.getDetails()); //output: BMW bike is BLACK
console.log(bikeObj2.getDetails()); //output: BMW bike is WHITE

In the above example, we are creating two objects, bikeObj1, bikeObj2 employing a constructor. In JavaScript, every object has its own methods and properties. In our example, two objects have two instances of the constructor function getDetails(). It doesn’t add up having a replica of getDetails doing an equivalent thing.
Instead of employing a copy of instances, we are getting to use the prototype property of a constructor function.

Prototype

When an object is made in JavaScript, JavaScript engine adds a __proto__ property to the newly created object which is named dunder proto. dunder proto or __proto__ points to the prototype object of the constructor function.

function Bike(model,color){
  this.model = model,
  this.color = color
}Bike.prototype.getDetails = function(){
 return this.model+" bike is "+this.color;
}
var bikeObj1 = new Bike(‘BMW’,’Black’);console.log(bikeObj1.getDetails());

The bikeObj1 object, which is made using the Bike constructor function, features a dunder proto or __proto__ property which points to the prototype object of the constructor function Bike.

In below code, both bikeObj1 it's dunder proto or __proto__ property and Bike.prototype property is equal. Let’s check if they point at an equivalent location using === operator.

console.log(bikeObj1.__proto__ === Bike.prototype );//output : true                                                

TK [Not sure what the author intends to mention here] So using prototype property, what percentage objects are created functions are loaded into memory just one occasion and that we can override functions if required. JavaScript Prototype