The official TypeScript decorator proposal defines a method decorator as follows:
"A method decorator function is a function that accepts three arguments: The object that owns the property, the key for the property (a string or a symbol), and optionally the property descriptor of the property. The function must return either undefined, the provided property descriptor, or a new property descriptor. Returning undefined is equivalent to returning the provided property descriptor".
— Ron Buckton, Decorators Proposal - TypeScript
The method decorator is like the class decorator, but it is used to override a method, as opposed to using it to ...
