Use of 'prototype' vs. 'this' in JavaScript?

javascript

prototype-engineering

this-keyword

javascript-best-practices

byNikita Barsukov·Jan 10, 2025

Maximize memory use and performance by leveraging prototype for shared functionality across all instances. Use this for meaningful individual properties unique to each instance.

function MyObject() {
  this.instanceProp = 'unique'; // just like you
}
MyObject.prototype.sharedMethod = function() {
  /* it's a party and everyone's invited */
};

Understanding prototypal inheritance is pivotal in JavaScript. When using the new operator, an instance's __proto__ gets linked to its constructor's prototype, optimizing performance and memory utilization.

Deep dive into 'Prototype' and 'This'

Implications for memory and performance

prototype enables shared methods across instances, reducing memory demands. If functions are defined here, changes impact all instances—an economical approach to memory use.

Conversely, using this within constructor functions attaches unique properties to each instance, increasing memory usage. While great for instance-specific needs, it's not ideal for memory management. 🧐

Foundations within constructor functions

In a constructor function, this sets initial values, unique to each instance. Prototype, however, benefits all instances since methods placed on the prototype are shared, optimizing memory.

JSON Serialization: a quirk to note

When serializing to JSON, utility found in the prototype chain is lost, because methods aren't included. You'll have to manually attach them after de-serializing.

Code Maintainability with IIFE

Immediate invoked function expressions (IIFE) hold great value—for defining and containing methods within a closure, maintaining state without cluttering global scope.

Prototype Changes: Watch the Dominoes Fall

Modifying an object's prototype impacts all objects derived from that prototype. This means alterations, additions, or subtractions to methods will affect all instances.