Develop Reference

Enable binding breaks when observable array updated via Ajax success callback

http://jsfiddle.net/FZ6K6/24/
I have a button (Remove inputs) with enable and css bindings that are returned when an observable array contains more than 2 items.
<button data-bind="click: removeInput, enable: Integers().length >2, css { red: Integers().length >2 }">Remove Input</button>
I also have a function (loadIntegerSorter) that sets the observable array to contain 2 items.
self.loadIntegerSorter = function () {
self.Integers([new integer(0, 0, 0), new integer(0, 0, 0)]);
};
I also have a save function that submits via ajax. Within the success callback, loadIntegerSorter is called.
success: function (result) {
if (result.Status == "success") {
isvm.loadSortedIntegers();
}
}
However, this seems to break the enable binding. The CSS binding behaves as expected with the array items = 2. But the Enable binding does not. I can run loadIntegerSorter outside of the Ajax function successfully so I suppose this is a synchronization problem but I don't know what the solution is.
The fiddle I've linked to doesn't fully demonstrate the problem because it depends on making a genuine Ajax request. But I hope it shows enough to understand.
Elaboration:
This results in the expected behaviour from the enable binding:
self.save = function () {
self.isloading();
};
But this doesn't:
self.save = function () {
$.ajax("/Home/Index", {
data: ko.toJSON(self.integerSorter),
cache: false,
type: "post",
contentType: "application/json",
context: self,
success: function (result) {
this.isloading();
}
});
};
And nor does this:
self.save = function () {
self.isloading();
$.ajax("/Home/Index", {
data: ko.toJSON(self.integerSorter),
cache: false,
type: "post",
contentType: "application/json",
context: self,
success: function (result) {
}
});
};
Whatever the cause of the problem, it seems to be related to the ajax call.

1)
Inside of your self.save function you're calling
self.isLoading(true);
Which yields
TypeError: 'undefined' is not a function (evaluating
'self.isLoading(true)')
telling you that self.isLoading is not declared anywhere in your code. This will break code execution even before the ajax request is sent.
2)
Same as 1) but this time for self.msgbox.status(). Undeclared: will break your code.
3)
The function self.loadIntegerSorter appears as self.loadSortedIntegers in the success function. Also, the self.save function appears declared two times. The second one will ovverride the first, but I guess the first one is there just in the fiddle.
4)
Inside of the success function, result.Status doesn't have any sense. You must understand that result is just a string of plain text, accessing the Status property of a string will result in an error. Perhaps you expect the response to be a JSON object with a Status property? If that is the case, you have to deserialize the string either by yourself (JSON.parse(response)) or by telling jQuery to do that for you (replace $.ajax with $.getJSON).
However, it may also be that you're not receiving any JSON back and you just wanted to access the response status, assuming you could do it that way. You can't. Being inside of a success function, you already know that your request has been successfully sent and a response received. No need to check it again.
5)
You're calling the loadSortedIntegers() method on the variable isvm. That's a totally wrong approach, even if it should work now it may cause huge troubles in the future. isvm is a global variable you use to contain an instance of your viewModel. The success function is contained in the viewModel itself, you should access it's own methods with this or self. A class should not access an instance of itself with a global variable. Question: how can I make this and/or self available in the success function? this can be reached by setting the context property to your $.ajax object. Exactly as you write success: function(){} you should write, just before that, context: this or, in your case, context: self.
Do that, and then just change the success function contents with this.loadSortedIntegers().
I've took the liberty to make some edits to your fiddle. Take your time to examine the difference here and to run it here.

Try to use valueHasMutated to push update for observable directly:
self.loadIntegerSorter = function () {
self.Integers([new integer(0, 0, 0), new integer(0, 0, 0)]);
self.Integers.valueHasMutated();
};

Variables in js

I am quite a noob in regards to js and today I come across bit of js I don't really understand and I would like to. Could you please shed some light ? There is Kendo involved but the question is plain js.
I have a nested grid, eg. each row can expand into other grid and each of this grid has its own datasource. I populate the datasources via the method below one by one as user clicks and I had a problem with forcing the datasource to read when it receives async response from the create call. (calling the read is pretty much incorrect thing to do, but Kendo has its own bugs - not a point here.). My problem was, I didn't have an instance to call the read() on, the method only returns datasource and assigns it to a grid, when the event comes back I can't find any reference to anything I could get the correct datasource instance from. this is different context in here.
In order to resolve this I added a datasource variable into the method what builds the datasource and I return the variable instead the datasource, which is the same thing. However this helps to have something to call the problematic read() on. Now in my create handler I call create on the variable I am returning in the method during innit. Well it works, but I am not sure if every datasource is calling read on its own instance after innit ?
function _getDatasource() {
var datasource = new kendo.data.DataSource({
transport: {
read: {
url: serviceBaseUrl + "ReadQuestionnaire",
dataType: "json",
type: "POST",
contentType: "application/json; charset=utf-8",
},
create: {
url: serviceBaseUrl + "CreateQuestionnaire",
dataType: "json",
type: "POST",
contentType: "application/json; charset=utf-8",
complete: function (jqXhr, textStatus) {
if (CheckForExceptions(jqXhr, textStatus) == false) {
// this is the variable I am not sure about
// after innit does this always refers to this same datasource ?
datasource.read();
}
}
}
}
});
return datasource;
}

Your solution is correct, and yes, the datasource.read() call is the correct datasource object in each case.
Here's why this works: closures.
A closure is the ability to have a variable declared in one function accessible from a nested function. Or, for a more accurate description, see the wikipedia page: http://en.wikipedia.org/wiki/Closure_(computer_science)
Here's a very simple example:
function doStuff(){
var name = "Derick";
function sayMyName(){
console.log(name);
}
sayMyName();
}
doStuff();
In this example, I'm declaring a variable name inside of the doStuff function. Then I'm nesting another function inside of the first function. The sayMyName function is accessing the name variable through the use of a closure.
When I call doStuff(), the variable is defined and assigned to a value. Then the sayMyName function is defined and it uses that variable. I then call sayMyName() and it logs the name to the console.
Similarly, in your code you are creating a variable that is assigned to the instance of the DataSource. Later, you are defining a function for the complete callback. After the data source has loaded and the complete callback is fired, you are accessing the same dataSource variable that you had assigned to the DataSource instance through the use of a closure around that variable.
Since you are declaring var dataSource every time you call _getDataSource, you are creating a new variable / reference, assigned to a new DataSource instance. I don't think you need to return datasource at the bottom of your function, though... at least, not for the complete callback function to work. Maybe you need it for something else, outside of this function, though?
For more information on closures in JavaScript:
https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Closures
How do JavaScript closures work?
http://www.javascriptkit.com/javatutors/closures.shtml
http://www.watchmecode.net/javascript-scope (paid screencast)
HTH

JS Prototype scope with this/bind

I have the following code that creates an object in JavaScript. It uses prototype to define functions and constructors.
function objectClass(){
this.variables = new Array();
}
objectClass.prototype =
{
contructor: objectClass,
setInfo: function(){
$.ajax({
url: "info.json",
success: function(){
//for each json element returned...
this.variables.push(json[i]);
}
});
}
getInfo: function(){
return this.variables;
},
}
This is a similar example of what I am trying to do. I need to be able to return the array of variables when I call obj.getInfo(). It always throws an error. I believe it is because the "this" is referring to the scope of the ajax success function.
Any ideas on how to get it to reference the objects variable?

That's correct, the this value is not automatically passed and thus not set to the instance. To force this, you can use the context property that $.ajax accepts:
$.ajax({
context: this, // `this` is the instance here
This sets the this value inside the success callback to the one you specified.

javascript dynamic properties dissapears after succesfully declaring it from json - becomes empty object (not undefined)

var s = store.get('billablexxxx');
if (!s) {
if (false) {
s = {
"something" : 'Value', ....
}
}
}else {
s = new Object;
$.getJSON('Translation/GetIndexLabels', function(data) {
$.each(data, function(key, val) {
s[key] = val;
// temp[key] = val;
})}) ;
}
}
//here i use the variable
But where i use the variable, the dynamic properties dissapaered, it's not undefined but it's an empty object.
However, when it has been set in the $.getJSON() function, all values are added.
What did i do wrong?
Edit:
Fixed the problem by putting it into a function. When i posted the question, i was already close to the answer that i have looked for the last "hour" (weird javascript console results brought confusion).
Thanks for the advice!

The call to $.getJSON() is asynchronous, so the execution will reach the part where you "use the variable" before the asynchronous call completes.
The usual way to deal with this is to have the use of the variable inside a callback function that is referenced in the getJSON() call.
Here's the reference: http://api.jquery.com/jQuery.getJSON/

The getJSON method is asynchronous, it calls your function(data) once it has completed.
At the point which you are using s, the getJSON method has not yet returned so the properties of s have not been initialised.

Accessing a variable whose value is set in an AJAX function

I've got a problem. I've been trying to solve the problem of how to avoid using global variables. I decided to use an object with functions on it instead, and wrote a script accordingly. However, the script won't run as expected:
GetXML: function() {
$.ajax({
type: "GET",
url: "questions.xml",
dataType: "xml",
success: function(xml) {
this.xml=xml;
$(window).trigger("canUseXML");
var docLength = $(xml).find('Question').length + 1;
alert("this really is an '" + this.xml + "' and the actual doclength is: " + docLength)//This is the first alert I mention.
} //close success
});//close AJAX
alert("yes! this is still a: " +this.xml) //This is the second alert I mention.
},
If it all ran as expected, both alerts would result in an 'object XMLDocument' (a variable declared elsewhere in this line: this.xml = null;). The first runs as expected. However, the second, outside of that function, returns value "null". Why?
Thanks, Elliot Bonneville
P.S. I've been stuck on the seemingly simple question of passing variables between functions for a week.

In JavaScript "this" always refers to the “owner” of the function executed, or rather, to the object that a function is a method of. So your first and second "this" does not refer to the same thing.
Assuming that the "success" function executes before the second alert (which it probably doesn't). You could do something like this:
GetXML: function() {
var that=this;
.
.
and then use "that" instead of "this".

Scoping.
Once you travel outside of anonymous function(xml) this.xml no longer exists.

You have two problems:
Scoping: this inside the callback is not your object with GetXML as a member. Use something like me = this; in the constructor of your object and then use me instead of this to explicitely set the value.
You callback function waits for a success of your Ajax request, but the rest of the script is going on, which is the purpose of callbacks. So, the Ajax request is made, and then you do alert("yes! this is still a: " +this.xml), while the callback has not yet been executed.

This is probably happening because ajax takes time to process. Javascript doesn't wait for one request before executing the next command, so while AJAX is being called, its trying to figure out what happened to this.xml.