JavaScript Object Prototypes

In JavaScript, object prototypes play a crucial role in the language's prototype-based inheritance system. A prototype is an object from which other objects inherit properties and methods. Every object in JavaScript has a prototype, and these prototypes are linked together to form a prototype chain.

1. Prototypes in JavaScript:

• Definition: A prototype in JavaScript is an object that is associated with another object and serves as a fallback for properties and methods that are not directly found on that object.

• Object Creation: When an object is created, it is linked to a prototype. If a property or method is not found on the object itself, JavaScript looks up the prototype chain to find it.

2. Object Prototypes:

• Prototype Property: Every object in JavaScript has a special property called __proto__ (or [[Prototype]]), which points to its prototype.

  
  var myObject = {};
  console.log(myObject.__proto__); // Output: [Object: null prototype] {}
  
  

• Object.create(): The Object.create() method is used to create a new object with the specified prototype. It provides a cleaner way to set up prototypal inheritance.

  
  var personPrototype = { greet: function() { console.log('Hello!'); } };
  var person = Object.create(personPrototype);
  person.greet(); // Output: 'Hello!'
  
  

3. Prototype Chain:

• Definition: The prototype chain is a series of linked objects where each object serves as the prototype for the next one. It is traversed when properties or methods are accessed on an object.

• Inheritance: If an object doesn't have a particular property or method, JavaScript looks up the prototype chain until it finds the first object in the chain that contains the desired property or method.

4. Object.prototype:

• Ultimate Prototype: The Object.prototype is the ultimate prototype in the JavaScript environment. It provides basic methods and properties that are inherited by all objects.

• Base for Most Objects: Object.prototype serves as the prototype for many objects, including those created using the Object constructor or object literals.

Conclusion:

Understanding JavaScript object prototypes is essential for grasping how inheritance works in the language. Prototypes allow for the sharing of properties and methods across objects, promoting code reuse and a more efficient use of memory. The prototype chain enables a dynamic and flexible system of object-oriented programming in JavaScript.

Prototype Inheritance

All JavaScript objects inherit properties and methods from a prototype:

• Date objects inherit from Date.prototype
• Array objects inherit from Array.prototype
• Person objects inherit from Person.prototype

The Object.prototype is on the top of the prototype inheritance chain:

Date objects, Array objects, and Person objects inherit from Object.prototype.

Adding Properties and Methods to Objects

Sometimes you want to add new properties (or methods) to all existing objects of a given type.

Sometimes you want to add new properties (or methods) to an object constructor.

codespan">prototype property allows you to add new properties to object constructors:

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Using the prototype Property

The JavaScript prototype property allows you to add new properties to object constructors:

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}

Person.prototype.nationality = "English";

The JavaScript prototype property also allows you to add new methods to objects constructors:

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}

Person.prototype.name = function() {
  return this.firstName + " " + this.lastName;
};