tap with promise chains

I’d like to add tap variant to a promise chain (from composeP or pipeP) with the idea that the tap is dealing with a promise. Does a tapP function have any use? Or do we just do

var tapP = function (fn) {
     return function (promise) {
         return promise
             .then(function (x) {
                  fn(x);
                  return promise;
             });
     };
};

[davidchambers]

@stevenyap, I recommend a Fantasy Land -compatible Future or Task type such as the one provided by Fluture.

[CrossEye]

I agree with @davidchambers. The main point is that Future/Task implementations follow known laws and can be used in a manner consistent with many other types. Promise implementations generally do not.