The official decorators proposal defines a parameter decorator as follows:
"A parameter decorator function is a function that accepts three arguments: The object that owns the method that contains the decorated parameter, the property key of the property (or undefined for a parameter of the constructor), and the ordinal index of the parameter. The return value of this decorator is ignored".
- Ron Buckton, Decorators Proposal - TypeScript
The following type declares the signature of a parameter decorator:
declare type ParameterDecorator = (target: Object, propertyKey: string | symbol, parameterIndex: number) => void;
Please note that this signature ...