Gotcha with Anonymous Class Instances: When and How to Avoid this JavaScript Pitfall?

Anonymous Class Instance: A Pitfall in JavaScript

In ES6, programmers can define anonymous classes with the class keyword and immediately instantiate them with the new operator:

<code class="javascript">var entity = new class {
    constructor(name) { this.name = name; }
    getName() { return this.name; }
}('Foo');</code>

While this may appear convenient, it's crucial to understand its underlying behavior and potential drawbacks.

Behind the Scenes

Behind the scenes, the new class expression creates a new constructor function and prototype object each time it's evaluated. This is unlike regular class declarations, which define a single constructor and prototype that are shared among all instances.

Caveats

a. Excessive Memory Consumption:

With immediate instantiation, a new constructor and prototype are created every time an object is created using the new class expression. This can lead to unnecessary memory consumption, especially if numerous objects are instantiated.

b. Lack of Inheritance:

Objects created using the new class pattern don't inherit from the parent constructor or share a common prototype. Hence, they lose the benefits of classes, such as inheritance, method reuse, and polymorphism.

Singleton Object Misconception

Some developers may use this pattern to create singleton objects, but it's not effective. The constructor function is still accessible, and a second instance can be created using new entity.constructor, defying the purpose of a singleton.

Avoidance Recommendation

Due to these drawbacks, it's strongly advised against using the new class pattern. Instead, favor traditional object literals for simplicity, readability, and instantiation efficiency:

<code class="javascript">var entity = {
    name: 'Foo',
    getName() { return this.name; }
};</code>

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