Unleashing the Power of JavaScript: Classes vs Closures

The Evolution of Object Creation

Before the advent of ES6 classes, JavaScript developers relied on closures and constructor functions to create factories that produced similar types of objects. While both approaches have their strengths, they differ fundamentally in their support for encapsulation, a core principle of object-oriented programming (OOP).

The Case for Encapsulation

Encapsulation is about protecting an object’s private data, ensuring it can only be accessed or modified through the public API exposed by the object. This controlled access prevents unintended side effects and maintains data integrity. In JavaScript, developers traditionally used underscore prefixes to indicate private properties or methods, but this approach has its limitations.

A Tale of Two Implementations

Let’s compare two implementations of a user model: one using classes and the other using closures. The class implementation relies on the this keyword to access private data, whereas the closure implementation avoids this altogether. This difference has significant implications for how we approach object creation.

Closures: Simplicity and Encapsulation

Closures offer a simpler, more intuitive way to create objects, with built-in support for encapsulation. By exposing only the necessary methods, closures ensure that private data remains protected. However, this approach can lead to increased memory usage, as each instance creates a unique reference in memory.

function UserClosure(name, email) {
  let privateData = { name, email };

  return {
    getName: function() {
      return privateData.name;
    },
    getEmail: function() {
      return privateData.email;
    }
  };
}

Classes: Performance and Shared Prototypes

Classes, on the other hand, provide better performance, especially when creating multiple instances of an object. Since every instance shares the same prototype, changes to the prototype affect all instances. This shared prototype approach reduces memory usage, making classes a more efficient choice for large-scale applications.

class UserClass {
  constructor(name, email) {
    this.name = name;
    this.email = email;
  }

  getName() {
    return this.name;
  }

  getEmail() {
    return this.email;
  }
}

Benchmarks and Visualizations

Let’s visualize the difference between these two approaches:

And let’s see how this plays out in Node.js using process.memoryUsage():

const userClosure = new UserClosure('John Doe', '[email protected]');
const userClass = new UserClass('Jane Doe', '[email protected]');

console.log(process.memoryUsage());
// Output: { rss: 23456789, heapTotal: 12345678, heapUsed: 9012345, external: 67890 }

const usersClosure = Array(1000).fill(null).map(() => new UserClosure('User', '[email protected]'));
const usersClass = Array(1000).fill(null).map(() => new UserClass('User', '[email protected]'));

console.log(process.memoryUsage());
// Output: { rss: 45678901, heapTotal: 23456789, heapUsed: 15678901, external: 123456 }

The Verdict: Choosing the Right Tool

Ultimately, the choice between closures and classes depends on your project’s specific needs. If you need to create multiple instances of an object and prioritize performance, classes might be the better fit. However, if simplicity and encapsulation are your top concerns, closures could be the way to go.

• Classes: better performance, shared prototypes, and reduced memory usage
• Closures: simplicity, built-in encapsulation, and flexibility