How does the prototype chain work in JavaScript

In JavaScript, every object has a prototype. The prototype is a reference to another object that the current object inherits properties and methods from. When you try to access a property or a method on an object, JavaScript first looks for it on that object. If it doesn't find it, it follows the prototype chain, going up the chain of linked objects until it finds the property or method or reaches the end of the chain.

Here's how the prototype chain works:

  1. Object Prototypes:
    • Every object in JavaScript has a prototype, except for the base object, which is at the top of the prototype chain. The base object has methods and properties that are available to all objects through inheritance.
  2. Prototype Linkage:
    • Objects in JavaScript are linked to their prototypes through an internal property called __proto__ (or [[Prototype]] in specifications).
  3. Accessing Properties and Methods:
    • When you access a property or method on an object, JavaScript first looks for it directly on that object. If it doesn’t find it, it follows the __proto__ chain, checking the prototype of the current object.
  4. Chain Traversal:
    • If the property or method isn't found in the immediate prototype, JavaScript continues up the prototype chain, checking the __proto__ of each linked object until it finds the property/method or reaches the end of the chain (the base object).

            // Creating an object
            let myObject = {
              name: 'Alice'
            // Adding a property to the prototype of myObject
            let myPrototype = {
              greet() {
                console.log(`Hello, ${}!`);
            // Linking the prototype to myObject
            myObject.__proto__ = myPrototype;
            // Accessing a property/method
            myObject.greet(); // Output: 'Hello, Alice!'            

In this example:

  • myObject has a name property directly on itself.
  • It doesn't have a greet method directly, but since it's linked to myPrototype via __proto__, it can access the greet method defined in myPrototype.
Important Notes:
  • Changing the prototype (__proto__) of an object dynamically is generally not recommended due to potential side effects and performance implications.
  • The prototype property is often used in constructor functions to define the prototype of objects created by that constructor function.
  • JavaScript engines optimize prototype chains for efficient property lookups to improve performance.
  • Understanding the prototype chain is crucial for comprehending inheritance and object relationships in JavaScript.

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