We are trying to implement QUnit JavaScript tests for a JS-heavy web app. We are struggling to find a way to successfully test methods that involve jQuery AJAX requests. For example, we have the following constructor function (obviously this is a very simplistic example):
var X = function() {
this.fire = function() {
$.ajax("someURL.php", {
data: {
userId: "james"
},
dataType: "json",
success: function(data) {
//Do stuff
}
});
};
};
var myX = new X();
myX.fire();
We are trying to find a way to test the fire method, preferably with a stubbed URL instead of the real someURL.php.
The only obvious solution to me at the moment is add the URL, and the success callback, as arguments to the constructor function. That way, in the test, we can create a new instance of X and pass in the stub URL, and a callback to run when the stub returns a response. For example:
test("Test AJAX function", function() {
stop();
var myX = new X();
//Call the AJAX function, passing in the stub URL and success callback
myX.fire("stub.php", function(data) {
console.log(data);
start();
});
});
However, this doesn't seem like a very nice solution. Is there a better way?
With jQuery, you can use the xhr object that .ajax() returns as a promise, so you can add more handlers (see below) than just the single success, complete and error ones you define in the options. So if your async function can return the xhr object, you can add test-specific handlers.
As for the URL, that's a little trickier. I've sometimes set up a very simple Node server on localhost, which just serves canned responses that were copied from the real server. If you run your test suite off that same server, your URLs just need to be absolute paths to hit the test server instead of the production server. And you also get a record of the requests themselves, as a server sees them. Or you can have the test server send back errors or bad responses on purpose, if you want to see how the code handles it.
But that's of course a pretty complex solution. The easier one would be to define your URLs in a place where you can redefine them from the test suite. For instance:
/* in your code */
var X = function () {
this.fire = function () {
return $.ajax({ url: this.constructor.url, ... });
};
};
X.url = "someURL.php"; // the production url
/* in your tests */
X.url = "stub.php"; // redefine to the test url
Also, QUnit has an asyncTest function, which calls stop() for you. Add a tiny helper to keep track of when to start again, and you've got a pretty good solution.
Here's what I've done before
// create a function that counts down to `start()`
function createAsyncCounter(count) {
count = count || 1; // count defaults to 1
return function () { --count || start(); };
}
// ....
// an async test that expects 2 assertions
asyncTest("testing something asynchronous", 2, function() {
var countDown = createAsyncCounter(1), // the number of async calls in this test
x = new X;
// A `done` callback is the same as adding a `success` handler
// in the ajax options. It's called after the "real" success handler.
// I'm assuming here, that `fire()` returns the xhr object
x.fire().done(function(data, status, jqXHR) {
ok(data.ok);
equal(data.value, "foobar");
}).always(countDown); // call `countDown` regardless of success/error
});
Basically countDown is a function that counts down to zero from whatever you specify, and then calls start(). In this case, there's 1 async call, so countDown will count down from that. And it'll do so when the ajax call finishes, regardless of how it went, since it's set up as an always callback.
And because the asyncTest is told to expect 2 assertions, it'll report an error if the .done() callback is never called, since no assertions will be run. So if the call completely fails, you'll know that too. If you want to log something on error, you can add a .fail() callback to the promise chain.
If it's a unit test that can (and should) be run in isolation from the server side, you can simply "replace" $.ajax to simulate whatever behavior.
One easy example:
test("Test AJAX function", function() {
// keep the real $.ajax
var _real_ajax = $.ajax;
// Simulate a successful response
$.ajax = function(url, opts) {
opts.success({expected: 'response'});
}
var myX = new X();
// Call your ajax function
myX.fire();
// ... and perform your tests
// Don't forgot to restore $.ajax!
$.ajax = _real_ajax;
});
Obviously you can also perform a real ajax call with stubbed url/data:
// Simulate a successfully response
$.ajax = function(url, opts) {
opts.success = function(data) {
console.log(data);
start();
}
_real_ajax('stub.php', opts)
}
If you haven't a complex response, I prefer the first approach, because it is faster and easy to comprehend.
However, you can also take another way and put the Ajax logic in it's own method, so you can easily stub it during tests.
Related
I am writing some javascript that includes a series AJAX calls and I am looking for an elegant solution to the following issue: The goal of the script is to gather parameters and then execute an API call with these parameters. The very first time the call is executed there is one parameter that needs to be requested from the server - every subsequent call will use a stored value of this parameter. This is where the issue begins. I want a conditional AJAX call to be made only if this is the first time. I don't want to put the rest of the code into the success function of that AJAX call as that seems convoluted. I would like something like the following but due to the obvious asynchronous nature of the call I realize this is not possible. I also want to avoid having a synchronous call as this would cause the thread to block:
var myParameter;
if(!params.myParam.isStored) {
myParameter = getParamWithAjaxCall();
} else {
myParameter = params.myParam;
}
// Continue with the rest of execution here of which there is a lot of code
Sorry if this seems like an obvious question and I have looked into solutions using the following but I am looking for an experienced opinion on what the most elegant solution would be:
jQuery: when.done
jQuery: async: false
Passing a callback to the Ajax call
I would create a wrapper function which you pass your logic to as a callback in done(). Something like this:
function makeRequest(callback) {
if (!params.myParam) {
// retrieve param
$.ajax({
url: '/getParam',
success: function(data) {
params.myParam = data.param;
}
}).done(callback);
}
else {
// param already has a value...
callback();
}
}
makeRequest(function() {
// make your AJAX request here, knowing that params.myParam will have a value.
});
You could use promises like so (I have used JQuery promises here):
function ParameterValueProvider() {
var parameterValue;
return function() {
var deferred = $.Deferred();
if ( parameterValue === undefined ) {
$.ajax({
// ... ajax parameters go here
}).done(function(rsp) {
parameterValue = rsp;
deferred.resolve(parameterValue);
});
}
deferred.resolve(parameterValue);
return deferred;
}
}
// Your Application
(function() {
'use strict';
var getParam = ParameterValueProvider();
// this will get the value from server the firs time
// and subsequent calls will use the cached value
getParam().then(function() {
// subsequent ajax calls go here
});
}());
I have an asynchronous Ajax function which runs a command string at the server side and returns the result to the client. It calls a callback to process the result.
function ajaxCall(commandStr,callback){
var url=......//make a url with the command string
jquery.get(url,function(result){
//process the result using callback
callback(result);
});
}
The asynchronous call (ajaxCall) may take a while to be finished but I want it to do the same command after an interval (1000ms).
I want to write a function that is like this:
function ajaxCallRepeated(interval,commandStr,callback)
I tried closures like this:
function ajaxCallRepeated(interval,commandStr,callback){
//This feature uses closures in Javascript. Please read this to know why and how: http://jibbering.com/faq/notes/closures/#clSto
function callLater(param1,param2,param3){
return (function(){
ajaxCall(param2,function(out,err){
if(param3)param3(out,err);
var functRef = callLater(param1,param2,param3);
setTimeout(functRef, interval);
});
});
}
//the first call
var functRef = callLater(interval,commandStr,callback);
setTimeout(functRef, interval);
}
Then I call it like this:
ajaxCallRepeated(2000,"ls",function(result){
alert(result);
});
But it only runs the command 2 times.
How can I write a function that will reschedule itself after it is called as a callback of an asynchronous function?
PS. I want to fire another Ajax call after the previous one is finished. Also, it worth to mention that axashCallRepeated() will be called with various parameters, so several Ajax calls are running in parallel, but for each commandStr, there is only one Ajax call going on, and after the Ajax call returns, another one will be fired after X seconds.
I would not use setTimeout to trigger the second Ajax call ! Because you never know how long it will take and if it's finished !
As far as you tagged your question right and you ARE using jquery you should consider something like this:
$.ajax({
type: 'POST',
url: url,
data: data,
success: function(){
// The AJAX is successfully done, now you trigger your custom event:
$(document).trigger('myAjaxHasCompleted');
},
dataType: dataType
});
$(function(){
//somehwere in your document ready block
$(document).on("myAjaxHasCompleted",function(){
$.ajax({
//execute the second one
});
});
});
So this would ensure that the ajax post is DONE and was successful and now you could execute the second one. I know its not the exact answer to your question but you should consider on using something like this ! Would make it safer I guess :-)
The key to solve this problem is to save a reference to the closure itself and use it when scheduling the next call:
function ajaxCallRepeated(interval,commandStr,callback){
//This feature uses closures in Javascript. Please read this to know why and how: http://jibbering.com/faq/notes/closures/#clSto
function callLater(_interval,_commandString,_callback){
var closure=(function(){
ajaxCall(_commandString,function(out,err){
if(_callback)_callback(out,err);
setTimeout(closure,_interval);
});
});
return closure;
}
//now make a closure for every call to this function
var functRef = callLater(interval,commandString,callback);
//the first call
functRef();
}
It becomes easier to reason about if you separate things up a bit.
For example, the repetition logic doesn't have to know about AJAX or callbacks at all:
function mkRepeater(interval, fn, fnScope, fnArgs) {
var running;
function repeat() {
if (!running) return;
fn.apply(fnScope, fnArgs);
setTimeout(repeat, interval);
}
return {
start: function() { running = true; repeat(); },
stop: function() { running = false; }
};
}
You can use it like this:
var r = mkRepeater(2000, ajaxFunction, this, ["getStuff", callbackFn]);
r.start();
...
r.stop();
If I use a closure to define something is there a means of waiting so to speak until the variable is populated before moving on to the next bit.
Example:
var myVari = someFunction();
$.each(myVari, function(){/*code for each*/});
the function that defines myVari is an AJAX call, which can take a second or 4 (yea its not to fast) to define the variable. Problem is, before the AJAX call yields its results the $.each has already fired off and errored due to myVari being empty. Is there a better way to approach this scenario?
You should adapt your code so that you can pass a callback to someFunction, which you execute when the AJAX call is completed.
The only way you can wait for the AJAX call to complete is to change the call to synchronous, but this is heavily discouraged as it locks up the browser completely for the duration of the AJAX call.
Because you are already using the jQuery libary, this process of callbacks becomes a whole lot easier. Instead of returning the variable like you are at the moment, I'd return the jQuery AJAX object (which has a promise interface as of 1.6), so you can easily add callbacks to it:
function someFunction () {
return jQuery.ajax('some/url.php', {
// whatever
});
}
var myVari = someFunction();
myVari.done(function (data) {
$.each(data, function(){/*code for each*/});
});
If I understand what you are trying to do, then you could try your $.each inside the 'success' handler of your ajax call.
Rewrite someFunction to something like -
var myVari; //define this here or in whichever calling scope where it needs to be available.
$.ajax({
'url': 'http://..',
'type': 'GET', // or POST
'data': { } // whatever data you need to send
'success': function(data) {
myVari = process_the_server(data);
$.each(myVari, function() {...});
}
});
Use a callback, like this:
someFunction(function(myVari) {
$.each(myVari, function(){ /*code for each*/ });
});
Then redefine someFunction like this:
function someFunction(callback) {
var myVari;
/* ... */
/* calcuate myVari */
/* ... */
/* instead of returning it, pass it to the callback: */
callback(myVari);
}
The correct way is: Instead of running the each on its own, run it inside the ajax call.
You could, I suppose do:
function checkFunc() {
setTimeout(function() {
if(myVari) {
$.each(........);
} else {
checkFunc();
}
}, 1000);
}
That not really good coding practice, but it will work.
Given the following:
var doThings = (function ($, window, document) {
var someScopedVariable = undefined,
methods,
_status;
methods = {
init: function () {
_status.getStatus.call(this);
// Do something with the 'someScopedVariable'
}
};
// Local method
_status = {
getStatus: function () {
// Runs a webservice call to populate the 'someScopedVariable'
if (someScopedVariable === undefined) {
_status.setStatus.call(this);
}
return someScopedVariable;
},
setStatus: function () {
$.ajax({
url: "someWebservice",
success: function(results){
someScopedVariable = results;
}
});
}
};
return methods;
} (jQuery, window, document));
The issue is clear, this is an async situation were I would like to wait until someScopedVariable is not undefined, then continue.
I thought of using jQuery's .when() -> .done() deferred call but I cant seem to get it to work. I've also thought of doing a loop that would just check to see if its defined yet but that doesnt seem elegant.
Possible option 1:
$.when(_status.getStatus.call(this)).done(function () {
return someScopedVariable;
});
Possible option 2 (Terrible option):
_status.getStatus.call(this)
var i = 0;
do {
i++;
} while (formStatusObject !== undefined);
return formStatusObject;
UPDATE:
I believe I stripped out too much of the logic in order to explain it so I added back in some. The goal of this was to create an accessor to this data.
I would suggest to wait for the complete / success event of an ajax call.
methods = {
init: function () {
_status.getStatus.call(this);
},
continueInit: function( data ) {
// populate 'someScopedVariable' from data and continue init
}
};
_status = {
getStatus: function () {
$.post('webservice.url', continueInit );
}
};
You cannot block using an infite loop to wait for the async request to finish since your JavaScript is most likely running in a single thread. The JavaScript engine will wait for your script to finish before it tries to call the async callback that would change the variable you are watching in the loop. Hence, a deadlock occurrs.
The only way to go is using callback functions throughout, as in your second option.
I agree with the other answer about using a callback if possible. If for some reason you need to block and wait for a response, don't use the looping approach, that's about the worst possible way to do that. The most straightforward would be use set async:false in your ajax call.
See http://api.jquery.com/jQuery.ajax/
async - Boolean Default: true By default,
all requests are sent asynchronously
(i.e. this is set to true by default).
If you need synchronous requests, set
this option to false. Cross-domain
requests and dataType: "jsonp"
requests do not support synchronous
operation. Note that synchronous
requests may temporarily lock the
browser, disabling any actions while
the request is active.
If I have an ajax call off fetching (with a callback) and then some other code running in the meantime. How can I have a third function that will be called when both of the first 2 are done. I'm sure it is easy with polling (setTimeout and then check some variables) but I'd rather a callback.
Is it possible?
You could just give the same callback to both your AJAX call and your other code running in the meantime, use a variable to track their combined progress, then link them to a callback like below:
// Each time you start a call, increment this by one
var counter = 0;
var callback = function() {
counter--;
if (counter == 0) {
// Execute code you wanted to do once both threads are finished.
}
}
Daniel's solution is the proper one. I took it and added some extra code so you don't have to think too much ;)
function createNotifier() {
var counter = 2;
return function() {
if (--counter == 0) {
// do stuff
}
};
}
var notify = createNotifier();
var later = function() {
var done = false;
// do stuff and set done to true if you're done
if (done) {
notify();
}
};
function doAjaxCall(notify) {
var ajaxCallback = function() {
// Respond to the AJAX callback here
// Notify that the Ajax callback is done
notify();
};
// Here you perform the AJAX call action
}
setInterval(later, 200);
doAjaxCall(notify);
The best approach to this is to take advantage of the fact that functions are first-order objects in JavaScript. Therefore you can assign them to variables and invoke them through the variable, changing the function that the variable refers to as needed.
For example:
function firstCallback() {
// the first thing has happened
// so when the next thing happens, we want to do stuff
callback = secondCallback;
}
function secondCallback() {
// do stuff now both things have happened
}
var callback = firstCallback;
If both your pieces of code now use the variable to call the function:
callback();
then whichever one executes first will call the firstCallback, which changes the variable to point to the secondCallback, and so that will be called by whichever executes second.
However your phrasing of the question implies that this may all be unnecessary, as it sounds like you are making an Ajax request and then continuing processing. As JavaScript interpreters are single-threaded, the Ajax callback will never be executed until the main body of code that made the request has finished executing anyway, even if that is long after the response has been received.
In case that isn't your situation, I've created a working example on my site; view the source to see the code (just before the </body> tag). It makes a request which is delayed by the server for a couple of seconds, then a request which receives an immediate response. The second request's response is handled by one function, and the first request's response is later handled by a different function, as the request that received a response first has changed the callback variable to refer to the second function.
You are talking about a thing called deferred in javascript as #Chris Conway mentioned above. Similarly jQuery also has Deferred since v1.5.
Check these Deferred.when() or deferred.done()
Don't forget to check jQuery doc.
But to give you some idea here is what I am copying from that site.
$.when($.ajax("/page1.php"), $.ajax("/page2.php")).done(function(a1, a2){
/* a1 and a2 are arguments resolved for the
page1 and page2 ajax requests, respectively */
var jqXHR = a1[2]; /* arguments are [ "success", statusText, jqXHR ] */
if ( /Whip It/.test(jqXHR.responseText) ) {
alert("First page has 'Whip It' somewhere.");
}
});
//Using deferred.then()
$.when($.ajax("/page1.php"), $.ajax("/page2.php"))
.then(myFunc, myFailure);
Something like this (schematic):
registerThread() {
counter++;
}
unregisterThread() {
if (--counter == 0) fireEvent('some_user_event');
}
eventHandler_for_some_user_event() {
do_stuff();
}
You can do this easily with Google's Closure library, specifically goog.async.Deferred:
// Deferred is a container for an incomplete computation.
var ajaxFinished = goog.async.Deferred();
// ajaxCall is the asynchronous function we're calling.
ajaxCall( //args...,
function() { // callback
// Process the results...
ajaxFinished.callback(); // Signal completion
}
);
// Do other stuff...
// Wait for the callback completion before proceeding
goog.async.when(ajaxFinished, function() {
// Do the rest of the stuff...
});
You can join multiple asynchronous computations using awaitDeferred, chainDeferred, or goog.async.DeferredList.