Develop Reference

Can you alter a statement in a javascript function after is run once

I'm having a hard time figuring this out. I'd like the xxp.run.pause(); to be replaced by xxp.run.play(); after the initial code below is actioned by a user once. I've tried creating a closure but I'm not sure I set it up right. Any help would be very much appreciated.
doSkip: function() {
XXP.run.removeListener('canper', XXP.Skip);
XXP.run.currentTime = XXP.skipTo;
XXP.run.pause(); // this is what I would like to change
}

You may set a flag somewhere which records whether or not the doSkip function has been called before:
var hasSkip = false;
doSkip: function() {
XXP.run.removeListener('canper', XXP.Skip);
XXP.run.currentTime = XXP.skipTo;
if (!hasSkip) {
XXP.run.pause();
hasSkip = true;
}
else {
XXP.run.play();
}
}

You can wrap the function in an IIFE with a persistent variable that checks to see if it's been paused. This has the advantage over having a separate variable elsewhere because hasPausedOnce is only needed for the doSkip function - no need to populate the outer scope (which can have readers of your code worrying about whether hasPausedOnce is going to be altered elsewhere)
doSkip: (() => {
let hasPausedOnce = false;
return function() {
XXP.run.removeListener('canper', XXP.Skip);
XXP.run.currentTime = XXP.skipTo;
if (!hasPausedOnce) {
XXP.run.pause();
hasPausedOnce = true;
} else XXP.run.play();
};
})()

JavaScript Too much recursion error with facebook JavaScript SDK

i am sending FB.login request to facebook. but FB is not defined while javascript SDK is still loading core javascript resources.
so, i put a check to get FB variable
function check_FB_variable(){
if(typeof FB=='undefined'){
check_FB_variable();
}else{}
}
check_FB_variable();
But this approach gives me Too much recursion error.
so , i put this code as
function check_FB_variable(){
if(typeof FB=='undefined'){
setTimeout(check_FB_variable,600);
}else{}
}
check_FB_variable();
but in this approach the before timeout function make a call function moves down and gives error
FB.login not defined.
please, help.

I've used something similar to check if JQMobi exists, I don't know exactly why but I think the exception is thrown because you call the pointer to the function every time.
You should try checking in an interval like this (Untested):
var facebookChecker = window.setInterval(fbCheck, 200);
var fbCheck = function () {
if (typeof FB != 'undefined' && facebookChecker != null) {
window.clearInterval(facebookChecker);
facebookChecker = null;
// Whatever you want to do if facebook is loaded
// Example: InitFBLogin();
}
}
Or you could use a while statement (the one I used):
/*
* This JQ Fix tries to attach Jquery to a variable to ensure it exists.
* - Marvin Brouwer.
*/
var FixJQ = function () {
var JQFIX = null;
while (!JQFIX || JQFIX == null) {
try {
JQFIX = jQuery;
} catch (nothing) { jQuery = $; };
};
JQFIX = null;
return true;
};
if (FixJQ()) {
FixJQ = null;
};
The beauty of the last one is that you can put you next step below this, because it will wait until the while loop has finished.
I honestly do not know which one is better/faster but I’m sure the bottom one will work.

Solution to "this" reference changing inside callbacks?

One of the issues I've been encountering again and again is the reference to the this pointer changing. Take the below example. I want to create a Server object, and store the resolution of the camera as a property. This is not possible, as this.resolution applies to a property in the camera callback object instead of the Server object.
function Server(options) {
this.settings = options.settings;
this.camera = options.camera;
// Grab camera resolution
this.camera.getImageResolution(function(err, data) {
this.resolution = data;
});
}
Server.prototype.start = function() {
console.log(this.resolution); // This outputs an undefined variable error
}
In the past, I have worked around this by renaming this to self temporarily to call functions. This does not work when I am storing a value. I would need to to pass this into the callback, which I obviously cannot do.
Additionally, I cannot use apply, as that would not allow camera.getImageResolution to call its own methods.
What is the best route to take in solving this issue? Please ask for clarification if my question is vague.

function Server(options) {
var self = this;
self.settings = options.settings;
self.camera = options.camera;
// Grab camera resolution
this.camera.getImageResolution(function(err, data) {
self.resolution = data;
});
}
Server.prototype.start = function () {
return this.resolution;
}
var server = new Server({options: {...}, settings: {...}});
server.camera.getImageResolution();
// after getImageResolution's asynch method has completed
server.start() // === data parameter from getImageResolution's asynch method callback

Titanium mvc - call function and wait for result

I am currently in the process of making my first Titanium iPhone app.
In a model I got:
(function() {
main.model = {};
main.model.getAlbums = function(_args) {
var loader = Titanium.Network.createHTTPClient();
loader.open("GET", "http://someurl.json");
// Runs the function when the data is ready for us to process
loader.onload = function() {
// Evaluate the JSON
var albums = eval('('+this.responseText+')');
//alert(albums.length);
return albums;
};
// Send the HTTP request
loader.send();
};
})();
and I call this function in a view like:
(function() {
main.ui.createAlbumsWindow = function(_args) {
var albumsWindow = Titanium.UI.createWindow({
title:'Albums',
backgroundColor:'#000'
});
var albums = main.model.getAlbums();
alert(albums);
return albumsWindow;
};
})();
however it seems like the call to the model (which fetches some data using HTTP) doesn't wait for a response. In the view when I do the alert it haven't received the data from the model yet. How do I do this in a best-practice way?
Thanks in advance

OK,
Something like this,
function foo(arg1, callback){
arg1 += 10;
....
... Your web service code
....
callback(arg1); // you can have your response instead of arg1
}
you will call this function like this,
foo (arg1, function(returnedParameter){
alert(returnedParameter); // here you will get your response which was returned in above function using this line .... callback(arg1);
});
so here arg1 is parameter (simple parameter like integer, string etc ... ) and second argument is your call back function.
Cheers.

What you need is Synchronous call to web service, so that it will wait till you get the response from the service.
To achieve this in java script you have to pass callback function as parameter and get the return value in callback function instead of returning value by return statement.
Actually coding style you are using is new for me because i am using different coding style.
But the main thing is you have to use call back function to retrieve value instead of return statement. Try this and if you still face the problem than tell me i will try to give an example.

the callback way like zero explained is nicely explained, but you could also try to get it handled with events.
(function() {
main.ui.createAlbumsWindow = function(_args) {
var albumsWindow = Titanium.UI.createWindow({
title:'Albums',
backgroundColor:'#000'
});
var status = new object(), // eventlistener
got_a_valid_result = false;
// catch result
status.addEventListener('gotResult',function(e){
alert(e.result);
got_a_valid_result = true;
});
// catch error
status.addEventListener('error',function(e){
alert("error occured: "+e.errorcode);
git_a_valid_result = true;
});
var albums = main.model.getAlbums(status);
// wait for result
while (!got_a_valid_result){};
return albumsWindow;
};
})();
and your model may something like
main.model.getAlbums = function(status) {
var loader = Titanium.Network.createHTTPClient();
loader.open("GET", "http://someurl.json");
loader.onload = function() {
var albums = eval('('+this.responseText+')');
status.fireEvent('gotResult',{result:albums});
return albums;
};
loader.onerror = function(e){
status.fireEvent('error',{errorcode:"an error occured"});
};
// Send the HTTP request
loader.send();
};

Just as a suggestion, try to use JSON.parse instead of eval as there are risks involved with using eval since it runs all javascript code.

I think that the solution The Zero posted is likely better for memory management, but I'm not totally sure. If you do and eventListener, be aware of the following
(see https://wiki.appcelerator.org/display/guides/Managing+Memory+and+Finding+Leaks)
function doSomething(_event) {
var foo = bar;
}
// adding this event listener causes a memory leak
// as references remain valid as long as the app is running
Ti.App.addEventListener('bad:idea', doSomething);
// you can plug this leak by removing the event listener, for example when the window is closed
thisWindow.addEventListener('close', function() {
// to remove an event listener, you must use the exact same function signature
// as when the listener was added
Ti.App.removeEventListener('bad:idea', doSomething);
});

How to lock AJAX functions from overlapping?

I've got one function checkEvery15Seconds that runs every 15 seconds. It checks to see if new comments have been added to a page.
I've got a form that submits a new comment once the submit button is pressed, then displays the new comment on the page.
In the process of adding a new comment checkEvery15Seconds is querying the database at the same time, so I end up with duplicate comments on the page (not in the database though, this is purely a JavaScript issue).
How can I get my "submitComment" function to stop checkEvery15Seconds and restart it after the "submitComment" function has finished executing?

add a boolean called somewhat suspend15sCheck in a scope which is accessible by both functions. enable it while adding the comment and afterwards set it to false again.
in your 15sCheck-function you first have to check if you are allowed to check :-)
var suspend15sCheck = false;
function addComment()
{
suspend15sCheck = true;
// add comment on base of form data
suspend15sCheck = false;
}
function myTimer()
{
if(suspend15sCheck === false)
{
// add comments via ajax request
// remember to check if the comments who will be added already exist :-)
}
}

Simplest solution: use a flagging variable that you turn on and off. The first line of your "checkEvery15Seconds" function reads: if (!global_checkingEvery15Seconds) return;
Just set that variable (whatever you name it, global or object-bound) to true when you want the checking turned on, and off when you don't.

You'll need a status variable to indicate the current state of the comment ajax request
var requestComments = false;
if(requestComments === false) {
requestComments = true;
// make ajax request
// on ajax success/fail
requestComments = false;
}

Wrap it up in an object that allows other functions to set start/stop flags on it.
function My15SecondsObj() {
var objSelf = this;
//
this.run();
}
My15SecondsObj.Paused = false;
My15SecondsObj.prototype.run= function() {
if (!Paused)
{
// Do your call here
}
var _this = this;
setTimeout(function() { _this.run(); }, 15000);
}
Now when you want to use this object, just do
var myObj = new My15SecondsObj();
and when you want to pause it,
myObj.Paused = true;
and start it again by doing:
myObj.Paused = false;
Add some events if you want to get really crazy, so that other objects can subscribe to notifications about when the database updates have succeeded, etc...