Should Constructor Functions Return Promises?

Constructor Functions and Promises: A Practical Approach

Consider the scenario of creating a constructor function for a blogging platform with various asynchronous operations. The question arises: is it advisable to have the constructor function return a Promise instead of the object it was intended to create?

The Pros of Returning a Promise:

• Guaranteed Initialization: Promises allow the user to chain then handlers that are executed after the constructor has finished executing. This ensures that the object is fully initialized before any code attempts to access it.

The Cons of Returning a Promise:

• Disruption of the new Operator: Promises break the traditional behavior of constructor functions, which return the newly created object. This can lead to confusion and potential errors.
• Limited Immediate Access: The returned Promise means the object created by the constructor is not immediately available. Users may encounter issues when assuming it will be accessible directly after construction.

Alternative Approaches:

Instead of returning a Promise from the constructor, consider employing one of the following strategies:

• Separate Initialization Method: Create a method that explicitly initializes the object after construction. This allows the constructor to return the object immediately, while ensuring it is fully initialized before use:

var engine = new Engine({path: '/path/to/posts'});
engine.init().then(function() {
  // Object is now initialized.
});

• Static Factory Function: Use a static factory function to create and initialize the object asynchronously. This approach provides greater flexibility in data acquisition and simplifies the constructor:

Engine.create({path: '/path/to/posts'}).then(function(engine) {
  // Object is now initialized.
});

Conclusion:

While returning a Promise from a constructor function can offer certain benefits, it is generally considered a bad practice. By following the suggested alternative approaches, you can achieve the desired functionality without disrupting the expected constructor behavior.

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