如果一个promise从一个.fail()里面返回一个错误,那就传播一个拒绝

Question

我有以下代码:

var myFunc = function(id, obj, backupObj) {
  return update(obj) // this returns a promise
  .fail(function(err){
    // if update is rejected
    restore(id, backupObj); // i wish to run this
    // and return the error that 'update(obj)' threw and propagate it
    return Q.reject(err); // should it be thrown like this???
  });
}

这是处理update()错误并返回错误的正确方法,所以当myFunc()从任何地方调用它时,它可以传播并最终处理？例如,在链中执行:

var foo = function(id, obj) {
  var backupObj = {};

  return checkIfValidObj(obj)
  .then(function(_backupObj) {
    backupObj = _backupObj;
    return doSomethingElse(id, obj);
  })
  .then(function() {
    // here!
    return myFunc(id, obj, backupObj);
  });
}

然后,作为foo调用者,我想做一些错误处理,并能够捕获update(obj).fail()可能返回的错误:

foo()
.then(function() { /* everything worked as expected, so we are happy */ })
.catch(function(err){ 
   // I want this to be executed also if 'update(obj)' inside 'myFunc' was rejected!
});