'get' method of descriptor object of class method in javascript

Question

I am learning typescript on Udemy and the instructor is going through the method decorator to try to bind a method to the instance when it invoked in a event listener.

The way he did is to use decorator in TypeScript and amend the Property Descriptor.

Code is shown below.

function Autobind(_: any, _2: string, descriptor: PropertyDescriptor) {
    const originalMethod = descriptor.value;
    console.log(descriptor)
    console.log(originalMethod)
    const adjDescriptor: PropertyDescriptor = {
        configurable: true,
        enumerable: false,
        get() {
            const boundFn = originalMethod.bind(this);
            return boundFn;
        }
    }
    console.log(adjDescriptor)
    return adjDescriptor;
}

class Printer {
    message = 'This works!';

    @Autobind
    showMessage() {
        console.log(this.message);
    }
}

const p = new Printer();

const button = document.querySelector('button')!;
button.addEventListener('click', p.showMessage);

I have two questions on his method.

1. How the 'get' method of the property descriptor get invoked in this case?
2. Originally the descriptor has a value property which is the showMessage method. I am curious why he did not amend the value property. Instead, he is adding the get method to the descriptor and ignore the value property.