AngularJS - mixing HTTP and custom promises with recursion - angularjs

Question

I have written a function wrapper that returns cached values for HTTP responses. In a specific situation (marked by comment // <--HERE) I see inconsistent behavior. I'm frankly not sure what exactly the inconsistency is, but bottom line, when the cache expires (has_expired), it does not wait for the http get to return in the recursive call.
My guess is I haven't put a "return" somewhere on a promise but I can't find out where (and why). Do I need to put a return in front of localForage.removeItem (and if so why?)
function cache_or_http(url,key) {
if (dont_use_cache()) {
return $http.get(url);
}
var d = $q.defer();
localforage.getItem(key)
.then (function(data) {
if (data) { // exists
if (has_expired(data.created_at)) {
localforage.removeItem(key)
.then (function() {return cache_or_http(url,key);}) // <--HERE
.catch(function() {return do_error_handling();})
} else { // not expired
d.resolve(JSON.parse(data.value));
return d.promise;
}
} else {
// doesn't exist
return $http.get(url)
.then (function(data) {
cache_entry = {
'value': JSON.stringify(data),
'created_at': moment().toString()
};
localforage.setItem(key, cache_entry);
d.resolve(data);
return (d.promise);
});
} // doesn't exist
}); // getItem .then
return (d.promise);
}

Answer 1

There is no need to manufacture a new promise with $q.defer. The .then method of a promise already returns a promise.
function cache_or_http(url,key) {
̶v̶a̶r̶ ̶d̶ ̶=̶ ̶$̶q̶.̶d̶e̶f̶e̶r̶(̶)̶;̶
̲r̲e̲t̲u̲r̲n̲ localforage.getItem(key)
.then (function(data) {
if (data) { // exists
if (has_expired(data.created_at)) {
̲r̲e̲t̲u̲r̲n̲ localforage.removeItem(key)
.then (function() {return cache_or_http(url,key);}) // <--HERE
.catch(function() {return do_error_handling();})
} else { // not expired
̶d̶.̶r̶e̶s̶o̶l̶v̶e̶(̶J̶S̶O̶N̶.̶p̶a̶r̶s̶e̶(̶d̶a̶t̶a̶.̶v̶a̶l̶u̶e̶)̶)̶;̶
return JSON.parse(data.value);
}
} else {
// doesn't exist
return $http.get(url)
.then (function(data) {
cache_entry = {
'value': JSON.stringify(data),
'created_at': moment().toString()
};
̲r̲e̲t̲u̲r̲n̲ localforage.setItem(key, cache_entry);
̶d̶.̶r̶e̶s̶o̶l̶v̶e̶(̶d̶a̶t̶a̶)̶;̶
̶r̶e̶t̶u̶r̶n̶ ̶(̶d̶.̶p̶r̶o̶m̶i̶s̶e̶)̶;̶
});
} // doesn't exist
}); // getItem .then
̶r̶e̶t̶u̶r̶n̶ ̶(̶d̶.̶p̶r̶o̶m̶i̶s̶e̶)̶;̶
}
For more information, see
Is this a "Deferred Antipattern"?