According to this question, when we set the window.location, javascript will "stop" executing or turn into a race condition.
Sometimes we need to fire window.location = SOMESCH://xxx multiple times inside a WebView to send "Notifications" back to our app. For example setting window.location = myapp://loginButtonEnabled?e=1 to tell the app that the user had filled in some nessasary info and can start login. It seems to be impossible to do something like this:
function(){
window.location = myapp://loginButtonEnable?e=1;
window.location = myapp://hideHintView;
.....
window.location = myapp://theLastThing;
}
Only the last window.location = myapp://theLastThing will be fired and then the execution of Javascript will stop(though we stopped the redirecting in our app by returning NO in webView:shouldStartLoadWithRequest:navigationType:).
I found it interesting that PhoneGap made this possible by using a dispatching queue, but I still haven't figure out why it works, anybody knows the trick??
BTW, is there a simple way to "resume" the execution after setting location? It will be much better than using an operation queue.
You need to give the event loop a chance to respond to the location change each time. The typical way of doing this is using a setTimeout with a small/zero delay, which has the effect of moving execution to the next event loop tick. Try something like this:
var q=[];
function dequeue() {
window.location='myapp://'+q.shift();
if (q.length>0) setTimeout(dequeue,0);
}
function notifyApp(cmd) {
q.push(cmd);
if (q.length==1) setTimeout(dequeue,0);
}
notifyApp('loginButtonEnable?e=1');
notifyApp('hideHintView');
notifyApp('theLastThing');
As for javascript execution stopping, setting window.location shouldn't have this effect unless it actually results in a page change - perhaps try using the technique above and see if your javascript continues after the last notifyApp() call.
EDIT: Another approach to this issue is to create temporary iframes instead of changing the location of the current page - see for example
Triggering shouldStartLoadWithRequest with multiple window.location.href calls
Related
i have this function:
<script language="javascript">
function live(){
var d = $live;
var elm = document.getElementById("live");
if(d==1){
elm.style.display = 'block';
} else{
elm.style.display = 'none';
}
}
</script>
setInterval(function(){live();},10000);
and im just concerned about my page getting stuck after having it open on the browser for a while or causing my users browser to stop responding or anything like that. How safe is to use loops like this?
Is this what google or facebook use to show new notifications alerts on their page in real time? That seems to go pretty smoothly.
Thank you.
This isn't a loop in the traditional sense, it's really just a function which is called at a regular interval, so you are in the clear here. Just be careful that nothing increases the memory use each time it executes, as that is what will most likely be what will kill the user's browser.
Also, the setInterval needs to me in a script tag, otherwise it will show up on your page.
Use of setInterval is a common practice for showing notifications on websites. It wont hang your page, although you must clear the interval once it is no longer required. Say you have already shown the notification, so better hold the reference of setInterval so that you could clear it later.
var ref = setInterval(fn, 100);
clearInterval(ref);
I am trying to start 3 applications from a browser by use of custom protocol names associated with these applications. This might look familiar to other threads started on stackoverflow, I believe that they do not help in resolving this issue so please dont close this thread just yet, it needs a different approach than those suggested in other threads.
example:
ts3server://a.b.c?property1=value1&property2=value2
...
...
to start these applications I would do
location.href = ts3server://a.b.c?property1=value1&property2=value2
location.href = ...
location.href = ...
which would work in FF but not in Chrome
I figured that it might by optimizing the number of writes when there will be effectively only the last change present.
So i did this:
function a ()
{
var apps = ['ts3server://...', 'anotherapp://...', '...'];
b(apps);
}
function b (apps)
{
if (apps.length == 0) return;
location.href = apps[0]; alert(apps[0]);
setTimeout(function (rest) {return function () {b(rest);};} (apps.slice(1)), 1);
}
But it didn't solve my problem (actually only the first location.href assignment is taken into account and even though the other calls happen long enough after the first one (thanks to changing the timeout delay to lets say 10000) the applications do not get started (the alerts are displayed).
If I try accessing each of the URIs separately the apps get started (first I call location.href = uri1 by clicking on one button, then I call location.href = uri2 by clicking again on another button).
Replacing:
location.href = ...
with:
var form = document.createElement('form');
form.action = ...
document.body.appendChild(form);
form.submit();
does not help either, nor does:
var frame = document.createElement('iframe');
frame.src = ...
document.body.appendChild(frame);
Is it possible to do what I am trying to do? How would it be done?
EDIT:
a reworded summary
i want to start MULTIPLE applications after one click on a link or a button like element. I want to achieve that with starting applications associated to custom protocols ... i would hold a list of links (in each link there is one protocol used) and i would try to do "location.src = link" for all items of the list. Which when used with 'for' does optimize to assigning only once (the last value) so i make the function something like recursive function with delay (which eliminates the optimization and really forces 3 distinct calls of location.src = list[head] when the list gets sliced before each call so that all the links are taken into account and they are assigned to the location.src. This all works just fine in Mozilla Firefox, but in google, after the first assignment the rest of the assignments lose effect (they are probably performed but dont trigger the associated application launch))
Are you having trouble looping through the elements? if so try the for..in statement here
Or are you having trouble navigating? if so try window.location.assign(new_location);
[edit]
You can also use window.location = "...";
[edit]
Ok so I did some work, and here is what I got. in the example I open a random ace of spades link. which is a custom protocol. click here and then click on the "click me". The comments show where the JSFiddle debugger found errors.
With unload event of window, it is possible to show the user a confirmation dialog , let's say in a situation where there is an ongoing request you are waiting for to finish and navigating away from the page will terminate that request.
Is there a way to accomplish this with onpopstate of HTML5 history API? Or any other way with the same outcome?
I guess you could modify the behavior of pushState to ask for confirmation before pushing a new state :
// Store original pushState
var _pushState = window.history.pushState;
// Some bad global variable to determine if confirmation is needed
var askForConfirm = true;
// Modify pushState behavior
window.history.pushState = function() {
if(!askForConfirm || confirm('Are you sure you want to quit this page ?')) {
// Call original pushState
_pushState.apply(window.history,arguments);
}
};
I don't know if it helps in your situation, but Sammy.js, a popular hash-routing library has a before handler. I've used it in my application to record the previously accessed hash, and if it's the hash I want to stop them from leaving, return false will keep them on that page. You still need to rewrite the URL to display the previous page, but it seems to be working.
See my answer in this other thread for more info.
I'm using javascript to include some content served up from a php file on another server. However, this other service can sometimes get flaky and either take a long time to load or will not load at all.
Is there a way in JS to try to get the external data for x number of seconds before failing and displaying a "please try again" message?
<script type="text/javascript" src="htp://otherserver.com/myscript.php"></script>
Couple issues: you can use timeout thresholds with XMLHttpRequest (aka ajax), but then since it's on an otherserver.com you cannot use XMLHttpRequest (and support all A-grade browsers) due to the Same Origin Policy restriction.
If the script introduces any kind of global name (eg any variable name, function name, etc) You can try setTimeout to keep checking for it:
var TIMELIMIT = 5; // seconds until timeout
var start = new Date;
setTimeout(function() {
// check for something introduced by your external script.
// A variable, namespace or function name here is adequate:
var scriptIncluded = 'otherServerVariable' in window;
if(!scriptIncluded) {
if ((new Date - start) / 1000 >= TIMELIMIT) {
// timed out
alert("Please try again")
}
else {
// keep waiting...
setTimeout(arguments.callee, 100)
}
}
}, 100)
The problem as I see it is you cannot cancel the request for the script. Please someone correct me if I'm wrong but removing the <script> from the DOM will still leave the browser's request for the resource active. So although you can detect that the script is taking longer than x seconds to load, you can't cancel the request.
I think you may be out of luck.
The only way I can think of doing this is to create a proxy on another (PHP-enabled) server which will fetch the data for you, but will stop when a certain timeout limit has been reached (and it can just return an empty result).
This is purely, purely theoretical:
<script> tags can be dynamically inserted into the DOM, at which point the script will be fetched and processed. This dynamic script tag injection is how some achieve cross-domain "AJAX."
I would imagine you could declare a global variable var hasLoaded = false;. At the end of the script you are attempting to load you could set that variable to true hadLoaded=true;. After injecting the script tag into the DOM you could then kickoff a setTimeout() whose callback function checks to see if "hasLoaded" is set to true. If it isn't, you can assume the script has not yet loaded fully into the browser. If it has, you can assume it has loaded completely.
Again, this is theoretical, but if you test it be sure to report back, I'm very curious.
I think that the only way to do this is take the content of the file via ajax and then set a timer. If the request finishes before the timer you can evaluate the respons with eval(that's not the better solution anyway), otherwise you can stop the ajax request and write the error message.
I have some code that I'd like to run on a page. My problem is that I don't want it to be run more than once at any one point. It can run multiple times, but just not while another instance of itself is running. I'm using jQuery and loading ajax content.
I just need something that prevents users from clicking hundereds of times and building up the que and pinging my server heaps.
Is this possible?
Thanks.
If it's just the one function being called in different areas, sounds like you're just wanting some sort of basic semaphore test, e.g:
isRunning = false;
function whatever() {
if (!isRunning) {
isRunning = true;
$.ajax(...., function() {
isRunning = false;
});
}
}
This question looks slightly related.
RE your edit: It's also worth noting that whatever javascript solution you put in place here to avoid a barrage of requests should additionally be considered on the server side.
Just keep a variable to flag whether it's running or not:
var running = true;
... complete: function() { running = false; }
I think it would be more user-friendly if you disabled your controls for the time the ajax request is on its way.
This way not only would you be saved from mass clicking, but also the user would know that there is no point in killing the mouse.