let CIRCUIT_BREAKER_TRIP = { /* some data */ };

let breaker = promise => {
  let broken = false;

  promise.then(() => broken = true);

  return val => {
    if(broken) {
      throw CIRCUIT_BREAKER_TRIP;
    } else {
      return val;
    }
  };
};

let resetBreaker = err => {
  if(err !== CIRCUIT_BREAKER_TRIP) {
    throw err;
  }
}

let b = new Promise(resolve => {
  setTimeout(() => resolve(), 1000);
});


// If the XHR call takes more than a second, the breaker is tripped
// and `doSomething` is never resolved.
xhr(...).then(breaker(b)).then(doSomething);


// use the "resetBreaker" function to normalize breaker errors
// Here, if the XHR call takes less than a second, `doSomething` happens
// If it takes longer, it is skipped and the console log takes place
xhr(...)
  .then(breaker(b))
  .then(doSomething, resetBreaker)
  .then(() => console.log("This always happens."));