How to Extend Function Objects with ES6 Classes Using Closures and Extension Functions?

Extending Function with ES6 Classes

ES6 allows the extension of special objects, including the Function object. This means that it is possible to inherit from the Function object and create objects that can be called as functions. However, implementing the logic for these calls can be challenging, as the behavior of this when calling a function as a function is different than when calling it as a method.

Using a Closure to Access Instance Data

The traditional approach to this problem is to use a closure. A closure is a function that has access to the environment in which it was created. This allows the function to access the instance data of the class even when it is called as a function.

<code class="js">class Smth extends Function {
  constructor(x) {
    super(() => { return x; });
  }
}</code>

Using an Extension Function

Another approach is to use an extension function. An extension function is a function that can be used to extend the behavior of existing objects. In this case, we can use an extension function to create an extended version of the Function object that will allow us to access instance data when the object is called as a function.

<code class="js">class ExtensibleFunction extends Function {
  constructor(f) {
    return Object.setPrototypeOf(f, new.target.prototype);
  }
}

class Smth extends ExtensibleFunction {
  constructor(x) {
    super(() => { return x; });
  }
}</code>

This approach is more flexible than using a closure, as it can be used to extend any function, not just the Function object.

By using these techniques, it is possible to extend the Function object with ES6 classes and implement custom logic for function calls.

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