Modify class method arguments

Question

I am using two different libraries.

The first one provides the following class:

class VolumeLoader {
    load(string: string): Promise<any> // Returns a promise to attach callbacks
    // rest of methods
}

The second one is using the previous loader like this

const loader = new Loader()
loader.load(string, callback) // Provides an argument to attach callback (without promises)

How can I modify VolumeLoader so it can accept string, callback?

I CAN NOT MODIFY ORIGINAL CLASS

What I've tried:

// Creating a new class using the previous loader. The load function works but I lose the rest of methods.
class _VolumeLoader {
    loader = new VolumeLoader
    load (string, callback) {
        this.loader.load(string).then(callback)
    }
    // rest of methods are lost! :(
}

// Modifying directly the prototype
const OriginalVolumeLoader = VolumeLoader;
const _VolumeLoader = VolumeLoader

_VolumeLoader.prototype.load = function (string, callback) {
    OriginalVolumeLoader.prototype.load.call(this, string).then(callback)
}
// Creates an infinite loop, not sure why :(

None worked :(

Answer 1

You need to save the original load method alone to avoid the infinite loop. Doing OriginalVolumeLoader = VolumeLoader will only create another reference to the same class in memory, so changes to the OriginalVolumeLoader end up as changes to VolumeLoader too.

Use:

const origLoad = VolumeLoader.prototype.load;
VolumeLoader.prototype.load = function (string, callback) {
    origLoad.call(this, string).then(callback)
};