Related
I have a scenario where I am returning a promise.
The promise is basically triggered by an ajax request.
On rejecting the promise it shows an error dialog that there is a server error.
What I want to do is when the response code is 401, I neither want to resolve the promise nor reject it (because it already shows the error dialog). I want to simply redirect to the login page.
My code looks something like this:
function makeRequest(ur, params) {
return new Promise(function (resolve, reject) {
fetch(url, params).then((response) => {
let status = response.status;
if (status >= 200 && status < 300) {
response.json().then((data) => {
resolve(data);
});
} else {
if (status === 401) {
redirectToLoginPage();
} else {
response.json().then((error) => {
if (!error.message) {
error.message = constants.SERVER_ERROR;
}
reject({ status, error });
});
}
}
});
});
}
As you can see, if the status is 401, I am redirecting to the login page. The promise is neither resolved nor rejected.
Is this code OK, or is there any better way to accomplish this?
A promise is just an object with properties in Javascript. There's no magic to it. So failing to resolve or reject a promise just fails to ever change the state from "pending" to anything else. This doesn't cause any fundamental problem in Javascript because a promise is just a regular Javascript object. The promise will still get garbage collected (even if still pending) if no code keeps a reference to the promise.
The real consequence here is what does that mean to the consumer of the promise if its state is never changed? Any .then() or .catch() listeners for resolve or reject transitions will never get called. Most code that uses promises expects them to resolve or reject at some point in the future (that's why promises are used in the first place). If they don't, then that code generally never gets to finish its work.
Or if code is using await on the promise instead of .then(), then that function will just remain suspended forever on that await. The rest of the function will be dead code and will never execute.
It's possible that you could have some other code that finishes the work for that task and the promise is just abandoned without ever doing its thing. There's no internal problem in Javascript if you do it that way, but it is not how promises were designed to work and is generally not how the consumer of promises expect them to work.
As you can see if the status is 401, I am redirecting to login page.
Promise is neither resolved nor rejected.
Is this code OK? Or is there any better way to accomplish this.
In this particular case, it's all OK and a redirect is a somewhat special and unique case. A redirect to a new browser page will completely clear the current page state (including all Javascript state) so it's perfectly fine to take a shortcut with the redirect and just leave other things unresolved. The system will completely reinitialize your Javascript state when the new page starts to load so any promises that were still pending will get cleaned up.
I think the "what happens if we don't resolve reject" has been answered fine - it's your choice whether to add a .then or a .catch.
However, Is this code OK? Or is there any better way to accomplish this. I would say there are two things:
You are wrapping a Promise in new Promise when it is not necessary and the fetch call can fail, you should act on that so that your calling method doesn't sit and wait for a Promise which will never be resolved.
Here's an example (I think this should work for your business logic, not 100% sure):
const constants = {
SERVER_ERROR: "500 Server Error"
};
function makeRequest(url,params) {
// fetch already returns a Promise itself
return fetch(url,params)
.then((response) => {
let status = response.status;
// If status is forbidden, redirect to Login & return nothing,
// indicating the end of the Promise chain
if(status === 401) {
redirectToLoginPage();
return;
}
// If status is success, return a JSON Promise
if(status >= 200 && status < 300) {
return response.json();
}
// If status is a failure, get the JSON Promise,
// map the message & status, then Reject the promise
return response.json()
.then(json => {
if (!json.message) {
json.message = constants.SERVER_ERROR;
}
return Promise.reject({status, error: json.message});
})
});
}
// This can now be used as:
makeRequest("http://example", {})
.then(json => {
if(typeof json === "undefined") {
// Redirect request occurred
}
console.log("Success:", json);
})
.catch(error => {
console.log("Error:", error.status, error.message);
})
By contrast, calling your code using:
makeRequest("http://example", {})
.then(info => console.log("info", info))
.catch(err => console.log("error", err));
Will not log anything because the call to http://example will fail, but the catch handler will never execute.
As others stated it's true that it's not really an issue if you don't resolve/reject a promise. Anyway I would solve your problem a bit different:
function makeRequest(ur,params) {
return new Promise(function(resolve,reject) {
fetch(url,params)
.then((response) => {
let status = response.status;
if (status >= 200 && status < 300) {
response.json().then((data) => {
resolve(data);
})
}
else {
reject(response);
}
})
});
}
makeRequest().then(function success(data) {
//...
}, function error(response) {
if (response.status === 401) {
redirectToLoginPage();
}
else {
response.json().then((error) => {
if (!error.message) {
error.message = constants.SERVER_ERROR;
}
//do sth. with error
});
}
});
That means I would reject every bad response state and then handle this in your error handler of your makeRequest.
It works and isn't really a problem, except when a caller of makeRequest expects of promise to fulfil. So, you're breaking the contract there.
Instead, you could defer the promise, or (in this case) reject with status code/error.
The ECMAScript spec explains the purpose of promises and new Promise():
A Promise is an object that is used as a placeholder for the eventual results of a deferred (and possibly asynchronous) computation.
25.6.3.1 Promise ( executor )
NOTE The executor argument must be a function object. It is called for initiating and reporting completion of the possibly deferred action represented by this Promise object.
You should use promises to obtain future values. Furthermore, to keep your code concise and direct, you should only use promises to obtain future values, and not to do other things.
Since you’ve also mixed program control flow (redirection logic) into your promise’s “executor” logic, your promise is no longer “a placeholder for the results of a computation;” rather, it’s now a little JavaScript program masquerading as a promise.
So, instead of wrapping this JavaScript program inside a new Promise(), I recommend just writing it like a normal JavaScript program:
async function makeRequest(url, params) {
let response = await fetch(url, params);
let { status } = response;
if (status >= 200 && status < 300) {
let data = await response.json();
successLogic(data);
} else if (status === 401) {
redirectToLoginPage();
} else {
let error = await response.json()
if (!error.message) {
error.message = constants.SERVER_ERROR;
}
errorLogic({ status, error });
}
}
Here's the code:
vm.saveData = function(data) {
demoService.saveData(data, function(response) {
if (response.status === 200) {
principal.identity(true).then(function() {
$state.reload();
return toastr.success('Success');
});
}
return toastr.error('Failure');
});
}
On getting success response from the api, it should display only the 'success' message. But, instead it displays the 'failure' message first and then the 'success' message. What am I doing wrong? Do I have to put a timeout or is there something which I'm missing here?
If the status is 200 then you set up a promise to call success later on.
Regardless of what the status is (because it is outside of the if and you haven't used an else) you always call error.
Presumably you just want to move return toastr.error('Failure'); into an else
That's not how you setup promises. Promises uses .then(). You are simply using passing the function in as a callback.
vm.saveData = function(data) {
demoService
.saveData(data)
.then(success, error);
function success(response) {
principal.identity(true).then(function() {
$state.reload();
return toastr.success('Success');
});
}
function error(response) {
return toastr.error('Failure');
}
};
Many systems such as AJAX send multiple messages to indicate progress in the task. You want to ignore the earlier messages. The failure message is from the earlier events while the action is incomplete.
I found out my mistake. Adding 'return' resolved the issue.
'return principal.identity(true).then(function(){
//do something here
});'
vm.saveData = function(data) {
demoService.saveData(data, function(response) {
if (response.status === 200) {
return principal.identity(true).then(function() {
$state.reload();
return toastr.success('Success');
});
}
return toastr.error('Failure');
});
}
I have a scenario where I am returning a promise.
The promise is basically triggered by an ajax request.
On rejecting the promise it shows an error dialog that there is a server error.
What I want to do is when the response code is 401, I neither want to resolve the promise nor reject it (because it already shows the error dialog). I want to simply redirect to the login page.
My code looks something like this:
function makeRequest(ur, params) {
return new Promise(function (resolve, reject) {
fetch(url, params).then((response) => {
let status = response.status;
if (status >= 200 && status < 300) {
response.json().then((data) => {
resolve(data);
});
} else {
if (status === 401) {
redirectToLoginPage();
} else {
response.json().then((error) => {
if (!error.message) {
error.message = constants.SERVER_ERROR;
}
reject({ status, error });
});
}
}
});
});
}
As you can see, if the status is 401, I am redirecting to the login page. The promise is neither resolved nor rejected.
Is this code OK, or is there any better way to accomplish this?
A promise is just an object with properties in Javascript. There's no magic to it. So failing to resolve or reject a promise just fails to ever change the state from "pending" to anything else. This doesn't cause any fundamental problem in Javascript because a promise is just a regular Javascript object. The promise will still get garbage collected (even if still pending) if no code keeps a reference to the promise.
The real consequence here is what does that mean to the consumer of the promise if its state is never changed? Any .then() or .catch() listeners for resolve or reject transitions will never get called. Most code that uses promises expects them to resolve or reject at some point in the future (that's why promises are used in the first place). If they don't, then that code generally never gets to finish its work.
Or if code is using await on the promise instead of .then(), then that function will just remain suspended forever on that await. The rest of the function will be dead code and will never execute.
It's possible that you could have some other code that finishes the work for that task and the promise is just abandoned without ever doing its thing. There's no internal problem in Javascript if you do it that way, but it is not how promises were designed to work and is generally not how the consumer of promises expect them to work.
As you can see if the status is 401, I am redirecting to login page.
Promise is neither resolved nor rejected.
Is this code OK? Or is there any better way to accomplish this.
In this particular case, it's all OK and a redirect is a somewhat special and unique case. A redirect to a new browser page will completely clear the current page state (including all Javascript state) so it's perfectly fine to take a shortcut with the redirect and just leave other things unresolved. The system will completely reinitialize your Javascript state when the new page starts to load so any promises that were still pending will get cleaned up.
I think the "what happens if we don't resolve reject" has been answered fine - it's your choice whether to add a .then or a .catch.
However, Is this code OK? Or is there any better way to accomplish this. I would say there are two things:
You are wrapping a Promise in new Promise when it is not necessary and the fetch call can fail, you should act on that so that your calling method doesn't sit and wait for a Promise which will never be resolved.
Here's an example (I think this should work for your business logic, not 100% sure):
const constants = {
SERVER_ERROR: "500 Server Error"
};
function makeRequest(url,params) {
// fetch already returns a Promise itself
return fetch(url,params)
.then((response) => {
let status = response.status;
// If status is forbidden, redirect to Login & return nothing,
// indicating the end of the Promise chain
if(status === 401) {
redirectToLoginPage();
return;
}
// If status is success, return a JSON Promise
if(status >= 200 && status < 300) {
return response.json();
}
// If status is a failure, get the JSON Promise,
// map the message & status, then Reject the promise
return response.json()
.then(json => {
if (!json.message) {
json.message = constants.SERVER_ERROR;
}
return Promise.reject({status, error: json.message});
})
});
}
// This can now be used as:
makeRequest("http://example", {})
.then(json => {
if(typeof json === "undefined") {
// Redirect request occurred
}
console.log("Success:", json);
})
.catch(error => {
console.log("Error:", error.status, error.message);
})
By contrast, calling your code using:
makeRequest("http://example", {})
.then(info => console.log("info", info))
.catch(err => console.log("error", err));
Will not log anything because the call to http://example will fail, but the catch handler will never execute.
As others stated it's true that it's not really an issue if you don't resolve/reject a promise. Anyway I would solve your problem a bit different:
function makeRequest(ur,params) {
return new Promise(function(resolve,reject) {
fetch(url,params)
.then((response) => {
let status = response.status;
if (status >= 200 && status < 300) {
response.json().then((data) => {
resolve(data);
})
}
else {
reject(response);
}
})
});
}
makeRequest().then(function success(data) {
//...
}, function error(response) {
if (response.status === 401) {
redirectToLoginPage();
}
else {
response.json().then((error) => {
if (!error.message) {
error.message = constants.SERVER_ERROR;
}
//do sth. with error
});
}
});
That means I would reject every bad response state and then handle this in your error handler of your makeRequest.
It works and isn't really a problem, except when a caller of makeRequest expects of promise to fulfil. So, you're breaking the contract there.
Instead, you could defer the promise, or (in this case) reject with status code/error.
The ECMAScript spec explains the purpose of promises and new Promise():
A Promise is an object that is used as a placeholder for the eventual results of a deferred (and possibly asynchronous) computation.
25.6.3.1 Promise ( executor )
NOTE The executor argument must be a function object. It is called for initiating and reporting completion of the possibly deferred action represented by this Promise object.
You should use promises to obtain future values. Furthermore, to keep your code concise and direct, you should only use promises to obtain future values, and not to do other things.
Since you’ve also mixed program control flow (redirection logic) into your promise’s “executor” logic, your promise is no longer “a placeholder for the results of a computation;” rather, it’s now a little JavaScript program masquerading as a promise.
So, instead of wrapping this JavaScript program inside a new Promise(), I recommend just writing it like a normal JavaScript program:
async function makeRequest(url, params) {
let response = await fetch(url, params);
let { status } = response;
if (status >= 200 && status < 300) {
let data = await response.json();
successLogic(data);
} else if (status === 401) {
redirectToLoginPage();
} else {
let error = await response.json()
if (!error.message) {
error.message = constants.SERVER_ERROR;
}
errorLogic({ status, error });
}
}
I have a global error handler for my angular app which is written as an $http interceptor, but I'd like to take it a step further. What I'd like is for each $http call that fails (is rejected), any "chained" consumers of the promise should first try to resolve the error, and if it is STILL unresolved (not caught), THEN I'd like the global error handler to take over.
Use case is, my global error handler shows a growl "alert box" at the top of the screen. But I have a couple of modals that pop up, and I handle the errors explicitly there, showing an error message in the modal itself. So, essentially, this modal controller should mark the rejected promise as "handled". But since the interceptor always seems to be the first to run on an $http error, I can't figure out a way to do it.
Here is my interceptor code:
angular.module("globalErrors", ['angular-growl', 'ngAnimate'])
.factory("myHttpInterceptor", ['$q', '$log', '$location', '$rootScope', 'growl', 'growlMessages',
function ($q, $log, $location, $rootScope, growl, growlMessages) {
var numLoading = 0;
return {
request: function (config) {
if (config.showLoader !== false) {
numLoading++;
$rootScope.loading = true;
}
return config || $q.when(config)
},
response: function (response) {
if (response.config.showLoader !== false) {
numLoading--;
$rootScope.loading = numLoading > 0;
}
if(growlMessages.getAllMessages().length) { // clear messages on next success XHR
growlMessages.destroyAllMessages();
}
return response || $q.when(response);
},
responseError: function (rejection) {
//$log.debug("error with status " + rejection.status + " and data: " + rejection.data['message']);
numLoading--;
$rootScope.loading = numLoading > 0;
switch (rejection.status) {
case 401:
document.location = "/auth/login";
growl.error("You are not logged in!");
break;
case 403:
growl.error("You don't have the right to do this: " + rejection.data);
break;
case 0:
growl.error("No connection, internet is down?");
break;
default:
if(!rejection.handled) {
if (rejection.data && rejection.data['message']) {
var mes = rejection.data['message'];
if (rejection.data.errors) {
for (var k in rejection.data.errors) {
mes += "<br/>" + rejection.data.errors[k];
}
}
growl.error("" + mes);
} else {
growl.error("There was an unknown error processing your request");
}
}
break;
}
return $q.reject(rejection);
}
};
}]).config(function ($provide, $httpProvider) {
return $httpProvider.interceptors.push('myHttpInterceptor');
})
This is rough code of how I'd expect the modal promise call to look like:
$http.get('/some/url').then(function(c) {
$uibModalInstance.close(c);
}, function(resp) {
if(resp.data.errors) {
$scope.errors = resp.data.errors;
resp.handled = true;
return resp;
}
});
1. Solution (hacky way)
You can do that by creating a service doing that for you. Because promises are chain-able and you basically mark a property handled at the controller level, you should pass this promise to your service and it'll take care of the unhandled errors.
myService.check(
$http.get('url/to/the/endpoint')
.then( succCallback, errorCallback)
);
2. Solution (preferred way)
Or the better solution would be to create a wrapper for $http and do something like this:
myhttp.get('url/to/the/endpoint', successCallback, failedCallback);
function successCallback(){ ... }
function failedCallback(resp){
//optional solution, you can even say resp.handled = true
myhttp.setAsHandled(resp);
//do not forget to reject here, otherwise the chained promise will be recognised as a resolved promise.
$q.reject(resp);
}
Here the myhttp service call will apply the given success and failed callbacks and then it can chain his own faild callback and check if the handled property is true or false.
The myhttp service implementation (updated, added setAsHandled function which is just optional but it's a nicer solution since it keeps everything in one place (the attribute 'handled' easily changeable and in one place):
function myhttp($http){
var service = this;
service.setAsHandled = setAsHandled;
service.get = get;
function setAsHandled(resp){
resp.handled = true;
}
function get(url, successHandler, failedHandler){
$http.get(url)
.then(successHandler, failedHandler)
.then(null, function(resp){
if(resp.handled !== true){
//your awesome popup message triggers here.
}
})
}
}
3. Solution
Same as #2 but less code needed to achieve the same:
myhttp.get('url/to/the/endpoint', successCallback, failedCallback);
function successCallback(){ ... }
function failedCallback(resp){
//if you provide a failedCallback, and you still want to have your popup, then you need your reject.
$q.reject(resp);
}
Other example:
//since you didn't provide failed callback, it'll treat as a non-handled promise, and you'll have your popup.
myhttp.get('url/to/the/endpoint', successCallback);
function successCallback(){ ... }
The myhttp service implementation:
function myhttp($http){
var service = this;
service.get = get;
function get(url, successHandler, failedHandler){
$http.get(url)
.then(successHandler, failedHandler)
.then(null, function(){
//your awesome popup message triggers here.
})
}
}
I am putting catches at the end, but they are returning empty object in one particular instance at least. Is a catch necessary for anything unbeknownst, or is it just screwing me up?
$( document).ready(function(){
app.callAPI()//a chainable a RSVP wrapper around a jquery call, with its own success() fail() passing forward to the wrapper, so it will either be a resolved or rejected thenable to which is now going to be chained
.then(
function(env) {
//set the property you needed now
app.someSpecialEnvObj = env;
},
function(rejectMessage){
console.log('call.API() cant set some special env object..');
console.log(rejectMessage);
}
)
.catch(
function(rejectMessage){
if(rejectMessage){
//a just incase, DOES IT HAVE VALUE, for somebody that may have not done their homework in the parent calls?
console.log('you have some kind of legitimate error, maybe even in callAPI() that is not part of any problems inside them. you may have forgotton handle something at an early state, your so lucky this is here!)
} else {
console.log('can this, and or will this ever run. i.e., is there any value to it, when the necessity to already be logging is being handled in each and every then already, guaranteeing that we WONT be missing ANYTHING')
}
}
);
});
Is it wrong? or is there some kind of use for it, even when I still use an error/reject handler on all usages of .then(resolve, reject) methods in all parent chained then-ables?
EDIT: Better code example, I hope. I think I might be still be using some kind of anti-pattern in the naming, I rejectMessage in my e.g., it's the jqXhr object right?
So maybe I should be naming them exactly that or what? i.e. jqXhr? By the way, the reason I like to reject it on the spot inside each then(), if there was an error, is because this way I can copiously log each individual call, if there was a problem specifically there, that way I don't have to track anything down. Micro-logging, because I can.
Promises are helping opening up the world of debugging this way.
Here's the three examples I have tried. I prefer method1, and method2, and by no means am I going back to method3, which is where I started off in the promise land.
//method 1
app.rsvpAjax = function (){
var async,
promise = new window.RSVP.Promise(function(resolve, reject){
async = $.extend( true, {},app.ajax, {
success: function(returnData) {
resolve(returnData);
},
error: function(jqXhr, textStatus, errorThrown){
console.log('async error');
console.log({jqXhr: jqXhr, textStatus: textStatus, errorThrown: errorThrown});
reject({ jqXhr: jqXhr, textStatus: textStatus, errorThrown: errorThrown}); //source of promise catch data believe
}
});
$.ajax(async); //make the call using jquery's ajax, passing it our reconstructed object, each and every time
});
return promise;
};
app.callAPI = function () {
var promise =app.rsvpAjax();
if ( !app.ajax.url ) {
console.log("need ajax url");
promise.reject(); //throw (reject now)
}
return promise;
};
//method 2
app.ajaxPromise = function(){
var promise, url = app.ajax.url;
var coreObj = { //our XMLHttpRequestwrapper object
ajax : function (method, url, args) { // Method that performs the ajax request
promise = window.RSVP.Promise( function (resolve, reject) { // Creating a promise
var client = new XMLHttpRequest(), // Instantiates the XMLHttpRequest
uri = url;
uri = url;
if (args && (method === 'POST' || method === 'PUT')) {
uri += '?';
var argcount = 0;
for (var key in args) {
if (args.hasOwnProperty(key)) {
if (argcount++) {
uri += '&';
}
uri += encodeURIComponent(key) + '=' + encodeURIComponent(args[key]);
}
}
}
client.open(method, uri);
client.send();
client.onload = function () {
if (this.status == 200) {
resolve(this.response); // Performs the function "resolve" when this.status is equal to 200
}
else {
reject(this.statusText); // Performs the function "reject" when this.status is different than 200
}
};
client.onerror = function () {
reject(this.statusText);
};
});
return promise; // Return the promise
}
};
// Adapter pattern
return {
'get' : function(args) {
return coreObj.ajax('GET', url, args);
},
'post' : function(args) {
return coreObj.ajax('POST', url, args);
},
'put' : function(args) {
return coreObj.ajax('PUT', url, args);
},
'delete' : function(args) {
return coreObj.ajax('DELETE', url, args);
}
};
};
app.callAPI = function () {
var async, callback;
async =app.ajaxPromise() ; //app.ajaxPromise() is what creates the RSVP PROMISE HERE<
if(app.ajax.type === 'GET'){async = async.get();}
else if(app.ajax.type === 'POST') {async = async.post();}
else if(app.ajax.type === 'PUT'){async = async.put();}
else if(app.ajax.type === 'DELETE'){ async = async.delete();}
callback = {
success: function (data) {
return JSON.parse(data);
},
error: function (reason) {
console.log('something went wrong here');
console.log(reason);
}
};
async = async.then(callback.success)
.catch(callback.error);
return async;
};
//method 3 using old school jquery deferreds
app.callAPI = function () {
//use $.Deferred instead of RSVP
async = $.ajax( app.ajax) //run the ajax call now
.then(
function (asyncData) { //call has been completed, do something now
return asyncData; //modify data if needed, then return, sweet success
},
function(rejectMessage) { //call failed miserably, log this thing
console.log('Unexpected error inside the callApi. There was a fail in the $.Deferred ajax call');
return rejectMessage;
}
);
return async;
};
I also run this somewhere onready as another backup.
window.RSVP.on('error', function(error) {
window.console.assert(false, error);
var response;
if(error.jqXhr){
response = error.jqXhr;
} else {
//response = error;
response = 'is this working yet?';
}
console.log('rsvp_on_error_report')
console.log(response);
});
Edit error examples
//one weird error I can't understand, an empty string("")?
{
"jqXhr": {
"responseText": {
"readyState": 0,
"responseText": "",
"status": 0,
"statusText": "error"
},
"statusText": "error",
"status": 0
},
"textStatus": "error",
"errorThrown": "\"\""
}
//another wierd one, but this one comes from a different stream, the RSVP.on('error') function
{
"readyState": 0,
"responseText": "",
"status": 0,
"statusText": "error"
}
I am putting catches at the end
That's the typical position for them - you handle all errors that were occurring somewhere in the chain. It's important not to forget to handle errors at all, and having a catch-all in the end is the recommended practise.
even if I use onreject handlers in all .then(…) calls?
That's a bit odd. Usually all errors are handled in a central location (the catch in the end), but of course if you want you can handle them anywhere and then continue with the chain.
Just make sure to understand the difference between an onreject handler in a then and in a catch, and you can use them freely. Still, the catch in the end is recommended to catch errors in the then callbacks themselves.
they are returning empty object in one particular instance atleast.
Then the promise screwed up - it should never reject without a reason. Seems to be caused be the
if ( !app.ajax.url ) {
console.log("need ajax url");
promise.reject();
}
in your code that should have been a
if (!app.ajax.url)
return Promise.reject("need ajax url");
Is a catch necessary for anything unbeknownst?
Not really. The problem is that catch is usually a catch-all, even catching unexpected exceptions. So if you can distinguish them, what would you do with the unexpected ones?
Usually you'd set up some kind of global unhandled rejection handler for those, so that you do not have to make sure to handle them manually at the end of every promise chain.
I think the general question deserves a simple answer without the example.
The pedantic technical answer is 'no', because .catch(e) is equivalent to .then(null, e).
However (and this is a big "however"), unless you actually pass in null, you'll be passing in something that can fail when it runs (like a coding error), and you'll need a subsequent catch to catch that since the sibling rejection handler by design wont catch it:
.then(onSuccess, onFailure); // onFailure wont catch onSuccess failing!!
If this is the tail of a chain, then (even coding) errors in onSuccess are swallowed up forever. So don't do that.
So the real answer is yes, unless you're returning the chain, in which case no.
All chains should be terminated, but if your code is only a part of a larger chain that the caller will add to after your call returns, then it is up to the caller to terminate it properly (unless your function is designed to never fail).
The rule I follow is: All chains must either be returned or terminated (with a catch).
If I remember correctly, catch will fire when your promise is rejected. Since you have the fail callback attached, your catch will not fire unless you call reject function in either your fail or success callback.
In other words, catch block is catching rejection in your then method.