done-implementation-example-with-promises.js

function done_wrapper(fn){
  return function(value){
    fn(value);
    return value;
  };
}

function badlog(x){
  console.log(x);
  return 'return a complete nonsense string!';
}

var g = Promise.resolve(5)
  .then( done_wrapper( badlog ) )// protected usage
  .then( function(value){
    return value + 1;
  })
  .then( badlog );// unprotected usage

// logs: 5
// adds 1
// logs 6
// but g = Promise {
//  [[PromiseStatus]]: "resolved",
//  [[PromiseValue]]: "return a complete nonsense string!"
// }