Should Constructors Return Promises?

Is it Advisable to Return a Promise from a Constructor Function?

In the realm of programming, the constructor function plays a pivotal role in the creation of new objects. It serves to initialize critical properties and establish the object's initial state. However, a lingering question arises: should the constructor function return a Promise, potentially delaying the availability of the newly created object?

The Rationale for a Promise-Returning Constructor

The appeal of returning a Promise from a constructor emerges when the object's initialization requires asynchronous operations. Such operations may encompass fetching data, parsing files, or executing intricate computations. By leveraging Promises, the constructor can defer the object's readiness until these tasks are complete.

Drawbacks of Promise-Returning Constructors

Despite the allure of a Promise-returning constructor, it poses several drawbacks:

• Disruption of the "new" Operator: Constructors should exclusively return an instance of their class. Returning a Promise instead contravenes this convention, disrupting the flow of new operator-based object creation.
• Inheritance Complications: Constructors serve as the foundation for class inheritance. When a constructor returns a Promise, it complicates the inheritance hierarchy, potentially leading to unexpected behaviors.
• Constructor Aromatization: A constructor's primary function is to initialize the object's state. Executing asynchronous operations within the constructor dilutes its narrow focus.

Alternative Approaches

To address concerns associated with Promise-returning constructors, alternative approaches are recommended:

• Post-Initialization Method: Defer asynchronous operations to a dedicated method rather than the constructor. This allows the constructor to return an immediately available object and enables chaining of asynchronous operations using Promises.
• Factory Functions: Employ static factory functions to create objects, especially when the construction process involves multiple asynchronous steps. These functions can return Promises, offering greater flexibility and decoupling the object creation from its initialization.

Conclusion

While returning a Promise from a constructor function may seem appealing for asynchronous initialization, it is generally an unwise practice. The potential disruption of the new operator, inheritance complications, and deviation from the constructor's sole purpose outweigh the perceived benefits.

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