I am having some trouble with a bit of code. I have a function that does some stuff to some data, calls a remote system (activating a script on that system and passing in the data), and then makes another call to the same system to activate a different script (which acts on the data saved above). The problem is that the 1st call to the remote system appears to get lost in the execution.
This is being run in Safari, uses jquery; the function is tied to a button click, which is defined in the javascript code with an onclick function (i.e. it is not defined in the html button definition).
Here's a rough breakdown of the function (cleaned out for viewing purposes - I hope I left enough to make it clear):
function compareJSON() {
// loop through the objects, testing and changing data
// ...
dataSession=({ //build object for output });
$.each( dataSession.chapters , function( indexC, value ) {
//compare objects to some others, testing and changing data
});
// ...
//Call remote script on other system
urlString="url://blah.dee.com/Blar?script=SaveJSON&$JSONobject=";
window.location= urlString + JSON.stringify(dataSession);
//Call remote script on other system
window.location="url://blah.dee.com/Blar?script=EditJSON";
}
The last three lines of code are the two calls. It uses the window.location to actually trigger the remote system, passing the data through the URL. But I need BOTH scripts to get called and run. It appears that only the LAST script in the sequence ever gets run. If I switch them around it remains whatever is in last place.
Is there something about the window.location that doesn't actually process until the end of the function?
This script actually used to be a series of separate function calls, but I figured I was running into asynchronous execution that was causing the various script calls to not register. But once I put the code into this single function, it was still happening.
Any clues would be helpful.
Thanks,
J
Modifing the value of window.location is reserved exclusively for instances in which you'd like to cause a browser redirect.
It looks like you want to trigger a page request instead. You say you already have jQuery loaded, if so, you can trigger such a request using jQuery.get or a similar function.
For example:
// Loads the myscript.php page in the background
$.get('myscript.php');
// You can also pass data (in the form of an object as the second argument)
$.get('myscript.php', { name: "John", time: "2pm" });
Related
I'm completely new in javascript and I'm trying to understand its asynch nature. For this purpose here is my sample code :
$("#calculate-similarity").click(function(){
// assume input is an array whose length is larger than 0
var requestData={"uris":input,"limit":100};
client=new Ajax(requestData);
alert('inside .click function');
})
Ajax=function(requestData){
alert('inside ajax');
$.ajax({
url: 'http://localhost:8080/',
type:'POST',
dataType: 'json',
contentType: 'application/json',
data: JSON.stringify(requestData),
xhrFields: {
withCredentials: true
}
}).done(function(data) {
$("#ws-results").children().detach();
$("#ws-results").append('<table id="my-final-table"><thead><th>fname</th><th>furi</th><th>sname</th><th>suri</th><th>similarity</th></thead><tbody></tbody></table>');
$('#my-final-table').dynatable({
dataset: {
records:data
}
});
});
}
Now, above, I'm creating new Ajax() and inside of it, I'm making a ajax request. As far as I know its asynch event. Therefore, I though that, this request should be completed first of all, and then my other javascript lines (alert('inside .click function')) should be executed. In other words, I would expect :
1) alert inside ajax
2) show my datatable on the browser
3) alert inside .click function
However, I got with the following order :
1) alert inside ajax
2) alert inside .click function
3) show table on the browser
So, what do you suggest me to understand these concepts ? I've a solid background with several programming languages like c++ and java but this is my first time with web development and javascript.
EDIT
If I modify my .click function like below, do you say first of all always 10000 times hello will be printed out and then table will be shown ? Or table would be shown somewhere at the middle of logging ? I mean when the response comes, engine should wait first in order to show it ?
Modified code : (Let's remove all of the alert statements)
$("#calculate-similarity").click(function(){
// assume input is an array whose length is larger than 0
var requestData={"uris":input,"limit":100};
client=new Ajax(requestData);
for(var z=0;z<10000;z++){
console.log(z+'hi!');
}
})
As far as I know its asynch event. Therefore, I though that, this request should be completed first of all, and then my other javascript lines should be executed.
That is exactly the opposite of what it means.
The Ajax function will run. It will trigger an HTTP request. The Ajax function will finish. alert will run.
At some point in the future, the HTTP response will arrive and the done event handler will fire.
This is exactly the same principle as:
alert(1);
$("#calculate-similarity").click(function(){ alert(2); });
alert(3);
JavaScript doesn't wait for you to click on calculate-similarity before firing alert(3).
If I modify my .click function like below, do you say first of all always 10000 times hello will be printed out and then table will be shown ? Or table would be shown somewhere at the middle of logging ? I mean when the response comes, engine should wait first in order to show it ?
JavaScript won't interrupt a running function in order to execute a different (event handler) function. It will wait until it isn't busy before it goes looking for events.
new Ajax is object instantiation and it's synchronous. Therefore you get inside ajax as the first result because it happens when your Ajax object is instantiated, not to be confused with when the Ajax request is fired.
alert is executed synchronously, so that's the second thing you get.
$.ajax which wraps around XMLHttpRequest, responsible for firing the actual ajax request, is the only async part in your code and its result, which is encapsulated inside done, is what you get last.
In other words, I think the confusion comes from the fact that you introduce another layer of abstraction called new Ajax() which provide little actual value and a lot of confusion :P. inside ajax signal inside the instantiation of your Ajax object, not the firing of the actual request.
I'll try my best to explain it. Think of this more as an analogy, it's not exactly what's going on but I think it might help you understand:
alert('inside ajax'); - this is a blocking call, it will run and wait for you to click OK.
Then when you call Ajax, what you're essentially doing is saying "go make this web request when you have a chance, and when it finishes call my done method." That's a network operation. It could finish in 1 second, it could take many seconds. Rather than freezing up the whole browser, this is done "in the background." So that makes the UI remains responsive. At some point in the future the network request will finish. When it does, the function you specified in done will get called to let you know it finished. Think of making the Ajax request as adding it to a queue rather than actually connecting to the network. When the browser gets to it it will execute your request and wait for the server to respond. When it does, it will signal you to let you know.
Next you alert('inside .click function'); which displays the alert and blocks.
Like I said, that's not a technically accurate description of what's going on, but I'm hoping it helps you understand the principle of it.
I am trying to update a document using rpc service.
I have an xpage with a button. I want to click that button and by using CS javascript to setInterval and update a document field every 5 seconds.
I used the remote service control and the code is this:
<xe:jsonRpcService id="jsonRpcService1" serviceName="heartBeat">
<xe:this.methods>
<xe:remoteMethod name="send">
<xe:this.script><![CDATA[var db = session.getCurrentDatabase();
var heartView = db.getView("Heartbeats");
var doc:NotesDocument = heartView.getFirstDocument();
var vl = doc.getItemValueString();
if(vl==""){
doc.replaceItemValue("dummyH","z");
}else{
doc.replaceItemValue("dummyH",vl+"z");
}
doc.computeWithForm(false, false);
doc.save();]]></xe:this.script>
</xe:remoteMethod>
</xe:this.methods></xe:jsonRpcService>
The code of the button is this:
<xp:button value="Label" id="button1">
<xp:eventHandler event="onclick" submit="false">
<xp:this.script><![CDATA[setInterval(function(){heartBeat.send()},3000);]]></xp:this.script>
</xp:eventHandler></xp:button>
It doesnt work. I get no error but i also get no updates in the document... What is wrong in the code?
UPDATE
if i replace rpc script with a simple print("aaaaa") it works perfectly (i also followed the suggestions of Tim in the answer below, for my client side code).
when i use again my previous code i get the following javascript error:
Unable to load /Databases/Test/Mike/my1.nsf/RPCpage.xsp/mm?$$viewid=!dqducrahog! status:400
how can i access the database and documents from a remote service?
The syntax of RPC calls is slightly unusual; your call to heartbeat.send(), for example, does not actually call the remote send method. Rather, it returns a handle on a remote method descriptor... to actually call the remote method, you need to add a callback:
var remoteMethod = heartbeat.send();
remoteMethod.addCallback(function(response){
// handle whatever came back from the server
});
If, for instance, you designed your remote method to return whether or not the heartbeat was successful, a more complete example would look like this:
var heartbeatInterval = 3000;
var periodicHeartbeat = function() {
var remoteMethod = heartbeat.send();
remoteMethod.addCallback(function(response){
if (response.stillAlive) {
setTimeout(periodicHeartbeat, heartbeatInterval);
}
});
}
setTimeout(periodicHeartbeat, heartbeatInterval);
It's generally recommended to use setTimeout to initially schedule a deferred function, and then call setTimeout again from within that deferred function to schedule its own next execution, instead of using setInterval.
In this use case, however, this is particularly true because each remote method call is asynchronous, so with setInterval, you would eventually end up with request overlap, because each call requires at least a few milliseconds to complete.
Additionally, the preferred pattern of scheduling the next execution from inside the current allows you to check what the server sent back to determine whether to even bother continuing to send subsequent requests. Right now you're not returning any value from your remote method; if you change just the last line to:
return { stillAlive: doc.save() };
...then that JSON object will be automatically passed to your callback function as its first argument. Taking another look at one line from the prior example:
if (response.stillAlive) {
...so the RPC call only reschedules itself if the prior call succeeded. This probably isn't the precise behavior you want, but given that you can return data from the remote method, and the data that was returned is passed to your callback function, you can design a call and response approach that best fits your business specifications for this functionality.
Having said all that, you may want to take a look at the keepAlive component from the XPages Extension Library... it doesn't store heartbeat data in Domino documents, but if all you're trying to do is prevent idle sessions from expiring, it's a much simpler solution.
The problem
I am having is the following code will not update the tow select boxes "select1" and "select2", unless I have an alert immediately preceding the code.
Background info -
I am posting two variables to this page, "sel1val" and "sel2val", and I am assigning them to hidden input boxes with id's "sel1valtry" and "sel2valtry" respectively. I am assigning the values of these input boxes to the variables in the function and have named them "sel1val" and "sel2val". I can post more code if need be, but it is what I call "franken code"...haha! because I am a novice, it is assembled from many different styles of code.
Objective - what I am trying to achieve is to set two select boxes based upon the value of "sel1val" and "sel2val". The correct functionality is only obtained when I have an alert prior to the code.
Methods I have tried - I have left in some commented out code, to illustrate my attempts. I have been through many forums and that is where I got these ideas from. I suspect that the alert "reloads" the javascript part of the page, but I have no real basis for this. I have tried "document ready", variations of "window load", and even tried slowing things down with a delay, in case it was a timing issue. Each of the methods I have tried have resulted in the same outcome, whereby it only works with an alert.
I have achieved much success with my web based projects, and this would not have been possible without the invaluable resource in forums such as this one. I would like to thank anyone that has ever provided input/solutions, as without this I would never have been able to progress.
$(document).ready(function(){
// $(document).ajaxSuccess(function(){
// alert("AJAX request successfully completed");
// });
//$(window).load(function()
//window.onload = function()
//$(function ()
//Code goes here
//alert("got here");
//{
var sel1val = $("#sel1valtry").val()
var sel2val = $("#sel2valtry").val()
if (sel2val)
{
//alert("will not work without this alert"+sel1val);
//$("#select1").delay(2000).val(sel1val);
//$("#select1").val(sel1val);
$("#select1").prop('value',sel1val);
// var element = document.getElementById('select1');
// element.value = sel1val;
dochange('selection2', sel1val)
//var element = document.getElementById('select2');
// element.value = sel2val;
alert("will not work without this alert"+sel2val);
$("#select2").val(sel2val);
}
//}
});
//}
It seems like the dochange function is using some asynchronous API (like an AJAX call for example) which is setting value to the sel2val variable in its success callback. But since AJAX is asynchronous, this function returns immediately, not waiting for the server to return a response. By putting an alert you are blocking the execution of the next line of code and leaving enough time for the AJAX call to complete and assign a value to the sel2val variable.
The proper way to fix your code is to provide a callback to this function where you will perform the necessary actions:
dochange('selection2', sel1val, function(result) {
$("#select2").val(result);
});
And in your dochange function you will invoke this callback in the success event of your AJAX call.
I'm creating a website that will feature news articles. These articles will appear in two columns at the bottom of the page. There will be a button at the bottom to load additional news stories. That means that I need to be able to specify what news story to load. Server-side, I'm simply implementing this with a LIMIT clause in my SQL statement, supplying the :first parameter like so:
SELECT *
FROM news
ORDER BY `date` DESC
LIMIT :first, 1
This means that, client-side, I need to keep track of how many news items I've loaded. I've implemented this by having the function to load new information be kept in an object with a property holding the number of items loaded. I'm worried that this is somehow a race condition that I am not seeing, though, where my loadNewInformation() will be called twice before the number is incremented. My code is as follows:
var News = {
newInfoItems: 0,
loadNewInformation: function(side) {
this.newInfoItems += 1;
jQuery.get(
'/api/news/'+ (this.newInfoItems - 1),
function(html) {
jQuery('div.col'+side).append(html);
}
);
}
}
On page load, this is being called in the following fashion:
News.loadNewInformation('left');
News.loadNewInformation('right');
I could have implemented this in such a way that the success handler of a first call made another AJAX request for the second, which clearly would not be a race condition...but this seems like sloppy code. Thoughts?
(Yes, there is a race condition.)
Addressing Just the JavaScript
All JavaScript code on a page (excluding Web-Workers), which includes callbacks, is run "mutually exclusive".
In this case, because newInfoItems is eagerly evaluated, it is not even that complex: both "/api/news/0" and "/api/news/1" are guaranteed to be fetched (or fail in an attempt). Compare it to this:
// eager evaluation: value of url computed BEFORE request
// this is same as in example (with "fixed" increment order ;-)
// and is just to show point
var url = "/api/news/" + this.newInfoItems
this.newInfoItems += 1;
jQuery.get(url,
function(html) {
// only evaluated on AJAX callback - order of callbacks
// not defined, but will still be mutually exclusive.
jQuery('div.col'+side).append(html);
}
);
However, the order in which the AJAX requests complete is not defined and is influenced by both the server and browser. Furthermore, as discussed below, there is no atomic context established between the server and individual AJAX requests.
Addressing the JavaScript in Context
Now, even though it's established that "/api/news/0" and "/api/news/1" will be invoked, imagine this unlikely, but theoretically possible situation:
articles B,A exist in database
browser sends both AJAX requests -- asynchronously or synchronously, it doesn't matter!
an article is added to the database sometime between when
the server processes the news/0 request, and
the server processes the news/1 request
Then, this happens:
news/0 returns article B (articles B,A in database)
article C added
news/1 returns article B (articles C,B,A in database)
Note that article B was returned twice! Oops :)
So, while the race-condition "seems fairly unlikely", it does exist. A similar race condition (with different results) can occur if news/1 is processed before news/0 and (once again) an article is added between the requests: there no atomic guarantee in either case!
(The above race condition would be more likely if executing the AJAX requests in-series as the time for a new article being added is increased.)
Possible Solution
Consider fetching say, n (2 is okay!) articles in a single request (e.g. "/api/latest/n"), and then laying out the articles as appropriate in the callback. For instance, the first half of the articles on the left and the second half on right, or whatever is appropriate.
As well as eliminating the particular race-condition above by making the single request an atomic action -- with respect to article additions -- it will also result in less network traffic and less work for the server.
The fetch for the API might then look like:
SELECT *
FROM news
ORDER BY `date` DESC
LIMIT :n
Happy coding.
Yes, technically, this could create a race condition of sorts. The calls are asynchronous, and if the first got held up for some reason, the second could return first.
However, as you don't have a great deal that goes on in your callback functions that depend on the presence of the other 'side' being populated I don't see where it should cause you too much grief.
Shouldn't be any race conditions, must be something else wrong in your code. The counter is incremented before your .get() call, so prior to each get the counter should be incremented correctly. Short example to demostrate that it works when called sequentially: http://jsfiddle.net/KkpwF/
I reckon you're hinting at the newItemInfo counter?
Observations:
You're calling News.loadNewInformation twice, with a callback function which will be executed on AJAX completion.
The callback method you provide does not alter the News object.
In this case, you don't have to worry. The second call to News.loadNewInformation will only be executed once the first call completes - that is, excluding executing the callback method. Hence your newItemInfo counter will contain the correct value.
Try this:
loadNewInformation: function(side) {
jQuery.get(
'/api/news/'+ (this.newInfoItems++),
function(html) {
jQuery('div.col'+side).append(html);
}
);
}
A little (!) bit of background before I can get to the question :
I am implementing a web based search solution. Technology used: javascript (jquery), .net, html etc. etc.
All my web service calls are done through javascript (cross domain ws call). I have few sequential web service calls which all have different success callback function.
I am not able to digest - when i call those ws individually in seperate places they are returning me proper results but sequentially sometime they are giving and sometime not.
sample code: this is not giving expected results all the time.
function submitSearchRequest(_queryString, Stores) {
if (Stores[1].length>0) {
//generate 'searchRequestForArtifact' request object
getSearchResponse("successcallForArtifact", _searchRequestForArtifact);
}
if (Stores[2].length > 0) {
//generate 'searchRequestForPerson' request object
getSearchResponse("successcallForPerson", _searchRequestForPerson);
}
}
function successcallForArtifact(response)
{
//show the results
}
function successcallForPerson(response)
{
//show the results
}
}
If you need sequentially you will need to kick off each search only after one has returned. Currently you are making async calls, meaning it gets kicked off then continues with the code. Currently if the second call is simply faster the order will be off. You will either need to make a sync call or simply have the order enforced by calling the second search from the success function for the artifact.
If you are using JQuery which it seems you are you can set the async parameter to false which will force the order you want but it will slow the overall performance of your page. See this question.