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Object's function getting called while sending data via AJAX

Sending a plain javascript object with function via AJAX request results in invoking this function.
Why is that happening?
The problem does not occur when sending JSON data.
What is the best way to convert that object to JSON?
I enclose sample code that presents this behaviour.
var A = (function () {
function A(value) {
this.value = value;
}
A.prototype.getValue = function () {
console.log('getValue');
return this.value;
};
return A;
})();
$(document).ready(function () {
var a = new A(10);
var xhr = $.ajax("http://example.com/", {
data: a,
type: 'post',
error: function (data) {
console.log('error');
},
success: function (data) {
console.log('success');
},
crossDomain: true
});
}
Output of the code is:
getValue
success

This is because jQuery.param (used internally by jQuery.ajax) uses the return value of a function when serializing the request parameters. From the docs:
As of jQuery 1.3, the return value of a function is used instead of the function as a String.
Thus, when jQuery.param encounters your a object and sees the getValue property being a function, it calls the function and uses the (serialized) the return value.
Either way, why would you want to pass such a complex object as request data? If you don't want to pass that function along with the request data, you're better off creating a custom serialization function for your A class, such as:
A.prototype.serialize = function() {
return { value: this.value };
}
and use that instead:
var xhr = $.ajax("http://example.com/", {
data: a.serialize(),
// ...
});

Set Private Variable for Reuse In Encapsulated JavaScript function

I have a JavaScript function that is reading some data from a text file containing JSON. Ideally, I wanted to pass all the JSON data to a private variable within my encapulated function, so that if I was required to read the data again the variable could be used.
I don't want to be reading the text file everytime I'm need to make certain checks. To me, this doesn't sound good for performance.
Here's my code:
function someObj() {
var siteDataSet = null;
this.Init = function () {
populateData();
}
this.GetPageData = function () {
var props = new Array();
props[0] = siteDataSet.pagetitle;
props[1] = siteDataSet.week_no;
props[2] = siteDataSet.intro_text;
return props;
}
function populateData() {
$.ajax({
type: "GET",
url: "data.txt",
contentType: "application/json; charset=utf-8",
dataType: "json",
data: "",
success: function (result) {
siteDataSet = result;
},
error: function () { },
complete: function () { }
});
}
}
$(document).ready(function () {
o_obj = new someObj();
o_obj.Init();
var t = o_obj.GetPageData();
});
As you can see, I'm calling Init() to use jQuery Ajax to pass all JSON to a variable called siteDataSet. When I call GetPageData(), the siteDataSet variable is null when this should not be the case.
Am I approaching what I am trying to achieve in a completely absurd way?

It's probably because your ajax call happens asynchronously and has not yet completed when you attempt to access the variable. Typically, in a situation like that, your best bet is to use a promise which will tell your code to expect a result, since it has not yet been set.
There are several libraries that provide an implementation, such as: https://github.com/promises-aplus/promises-spec
As an alternative, could create a method you wish to be called on completion that will have all of the code you wish to execute and then pass it in. Something like:
function afterRetrieved(o_obj) {
var t = o_obj.GetPageData();
...
}
o_obj.Init(afterRetrieved);
That passes the function into your Init method to be executed after the data is retrieved. It would require a few changes to your implementation as below:
this.Init = function (fn) {
populateData(fn);
}
function populateData(fn) {
....
success: function (result) {
siteDataSet = result;
fn(this)
},
...
}
I'd imagine that either of those should resolve your issue.

Passing function name as a parameter to another function

I am calling a web services from client side on .aspx page, and I want to call a function on the success of this service.
The name of function will be passed as a parameter to this function, which will dynamically change.
I am passing it like this:
function funName parm1, parm2, onSucceedCallFuntion
function onSucceedCallFuntion(result)
//doing something here.
Perhaps because it's a string is why the "succeed" function could not be called
function funName(parm1, par2, onSucceedFunName) {
$.ajax({
url: "../WebServices/ServiceName.asmx/ServiceFunName",
data: JSON.stringify({
parm1: parm1,
par2: par2
}), // parameter map type: "POST", // data has to be POSTED
contentType: "application/json",
dataType: "json",
success: onSucceedFunName,
});
function onSucceedFunName() {}

If you're passing the name of the function as a string, you could try this:
window[functionName]();
But that assumes the function is in the global scope. Another, much better way to do it would be to just pass the function itself:
function onSuccess() {
alert('Whoopee!');
}
function doStuff(callback) {
/* do stuff here */
callback();
}
doStuff(onSuccess); /* note there are no quotes; should alert "Whoopee!" */
Edit
If you need to pass variables to the function, you can just pass them in along with the function. Here's what I mean:
// example function
function greet(name) {
alert('Hello, ' + name + '!');
}
// pass in the function first,
// followed by all of the variables to be passed to it
// (0, 1, 2, etc; doesn't matter how many)
function doStuff2() {
var fn = arguments[0],
vars = Array.prototype.slice.call(arguments, 1);
return fn.apply(this, vars);
}
// alerts "Hello, Chris!"
doStuff2(greet, 'Chris');

javascript prototype access this

I have a javascript 'class' which contains a wrapper method to call jquery .ajax(). I want to pass in the onSuccess and onError function handlers, but am not sure how. I can do this with plain old global functions, but I'm trying to improve my javascript (from Java background). Any pointers would be appreciated.
In the _makeAjaxCall() method below, how do I reference the onSuccessHandler
function testApp() {
new X();
}
function X() {
// Init X by making Ajax call, passing the func to be called on ajax return
this._makeAjaxCall(initUrl, this.onSuccessInit, this.onError);
// Make another ajax call to init another component
this._makeAjaxCall(initUrl, this.onSuccessSomeOtherAjaxCall, this.onError);
}
X.prototype.onSuccessInit = function(){
this.doStuff(...);
}
X.prototype.onSuccessSomeOtherAjaxCall = function(){
this.doOtherStuff(...);
}
/**
* make an ajax call, and call the provided success/error handler
*/
X.prototype._makeAjaxCall = function(url, onSuccessHandler, onError){
$.ajax({
url : url,
success : function (jsonData, textStatus, XMLHttpRequest) {
// If I don't user 'this', the func called but I've lost my reference
// to my instance of X
onSuccessHandler();
// If I use 'this', it points to the ajax call object, not to my X object.
this.onSuccessHandler();
}
});
}

The problem is that when the success callback is called by the $.ajax function, the default context is used window. You need to tell JQuery that you want a different context, so you can do one of 3 things:
Add a context attribute to the hash that is sent to $.ajax, so I your case you can do:
$.ajax({
url: url,
context: this, // this will tell JQuery to use the right context
success: this.onSuccessHandler
});
Use JQuery's $.proxy function, like:
$.ajax({
url: url,
success: $.proxy(this.onSuccessHandler, this) // this will bind the correct context to the callback function
});
Cache the variable this, like #mVChr suggested, although I would encourage you to use self as it has become somewhat of a javascript idiom
var self = this;
$.ajax({
url: url,
success: function(data) {
self.onSuccessHandler(data);
}
});
Edit:
If you need a more in depth explanation of context and scope in javascript checkout this article: http://www.digital-web.com/articles/scope_in_javascript/

Cache this within the local scope of _makeAjaxCall before conducting the ajax call:
X.prototype._makeAjaxCall = function(url, onSuccessHandler, onError){
var _X = this; // cache this
$.ajax({
url : url,
success : function (jsonData, textStatus, XMLHttpRequest) {
// use cached this
_X.onSuccessHandler();
}
});
}

Thanks to input from CarlosZ & mVChr, I've figured out the solution, http://jsfiddle.net/bX35E/3/
$(document).ready(function testApp() {
new X();
});
function X() {
console.dir(this);
var initUrl = "/echo/json/";
this._instanceVariable = "I AM defined!";
// Init X by making Ajax call, passing the func to be called on ajax return
this._makeAjaxCall(initUrl, this.onSuccessInit(), this.onError);
// Make another ajax call to init another component
this._makeAjaxCall(initUrl, this.onSuccessSomeOtherAjaxCall(), this.onError);
}
X.prototype.onSuccessInit = function(){
//this.doStuff(...);
var self = this;
return function() {
alert("onSuccessInit, _instanceVariable="+self._instanceVariable);
}
}
X.prototype.onSuccessSomeOtherAjaxCall = function(){
var self = this;
return function() {
alert("onSuccessSomeOtherAjaxCall, _instanceVariable="+self._instanceVariable);
}
}

jQuery pass more parameters into callback

Is there a way to pass more data into a callback function in jQuery?
I have two functions and I want the callback to the $.post, for example, to pass in both the resulting data of the AJAX call, as well as a few custom arguments
function clicked() {
var myDiv = $("#my-div");
// ERROR: Says data not defined
$.post("someurl.php",someData,doSomething(data, myDiv),"json");
// ERROR: Would pass in myDiv as curData (wrong)
$.post("someurl.php",someData,doSomething(data, myDiv),"json");
}
function doSomething(curData, curDiv) {
}
I want to be able to pass in my own parameters to a callback, as well as the result returned from the AJAX call.

The solution is the binding of variables through closure.
As a more basic example, here is an example function that receives and calls a callback function, as well as an example callback function:
function callbackReceiver(callback) {
callback("Hello World");
}
function callback(value1, value2) {
console.log(value1, value2);
}
This calls the callback and supplies a single argument. Now you want to supply an additional argument, so you wrap the callback in closure.
callbackReceiver(callback); // "Hello World", undefined
callbackReceiver(function(value) {
callback(value, "Foo Bar"); // "Hello World", "Foo Bar"
});
Or, more simply using ES6 Arrow Functions:
callbackReceiver(value => callback(value, "Foo Bar")); // "Hello World", "Foo Bar"
As for your specific example, I haven't used the .post function in jQuery, but a quick scan of the documentation suggests the call back should be a function pointer with the following signature:
function callBack(data, textStatus, jqXHR) {};
Therefore I think the solution is as follows:
var doSomething = function(extraStuff) {
return function(data, textStatus, jqXHR) {
// do something with extraStuff
};
};
var clicked = function() {
var extraStuff = {
myParam1: 'foo',
myParam2: 'bar'
}; // an object / whatever extra params you wish to pass.
$.post("someurl.php", someData, doSomething(extraStuff), "json");
};
What is happening?
In the last line, doSomething(extraStuff) is invoked and the result of that invocation is a function pointer.
Because extraStuff is passed as an argument to doSomething it is within scope of the doSomething function.
When extraStuff is referenced in the returned anonymous inner function of doSomething it is bound by closure to the outer function's extraStuff argument. This is true even after doSomething has returned.
I haven't tested the above, but I've written very similar code in the last 24 hours and it works as I've described.
You can of course pass multiple variables instead of a single 'extraStuff' object depending on your personal preference/coding standards.

When using doSomething(data, myDiv), you actually call the function and do not make a reference to it.
You can either pass the doStomething function directly but you must ensure it has the correct signature.
If you want to keep doSomething the way it is, you can wrap its call in an anonymous function.
function clicked() {
var myDiv = $("#my-div");
$.post("someurl.php",someData, function(data){
doSomething(data, myDiv)
},"json");
}
function doSomething(curData, curDiv) {
...
}
Inside the anonymous function code, you can use the variables defined in the enclosing scope. This is the way Javascript scoping works.

It's actually easier than everyone's making it sound... especially if you use the $.ajax({}) base syntax vs. one of the helper functions.
Just pass in the key: value pair like you would on any object, when you setup your ajax request... (because $(this) hasn't changed context yet, it's still the trigger for the bind call above)
<script type="text/javascript">
$(".qty input").bind("keypress change", function() {
$.ajax({
url: "/order_items/change/"+$(this).attr("data-order-item-id")+"/qty:"+$(this).val()+"/returnas.json",
type: "POST",
dataType: "json",
qty_input: $(this),
anything_else_i_want_to_pass_in: "foo",
success: function(json_data, textStatus, jqXHR) {
/* here is the input, which triggered this AJAX request */
console.log(this.qty_input);
/* here is any other parameter you set when initializing the ajax method */
console.log(this.anything_else_i_want_to_pass_in);
}
});
});
</script>
One of the reasons this is better than setting the var, is that the var is global and as such, overwritable... if you have 2 things which can trigger ajax calls, you could in theory trigger them faster than ajax call responds, and you'd have the value for the second call passed into the first. Using this method, above, that wouldn't happen (and it's pretty simple to use too).

In today's world there is a another answer that is cleaner, and taken from another Stack Overflow answer:
function clicked()
{
var myDiv = $( "#my-div" );
$.post( "someurl.php", {"someData": someData}, $.proxy(doSomething, myDiv), "json" );
}
function doSomething( data )
{
// this will be equal to myDiv now. Thanks to jQuery.proxy().
var $myDiv = this;
// doing stuff.
...
}
Here's the original question and answer:
jQuery HOW TO?? pass additional parameters to success callback for $.ajax call?

You can also try something like the following:
function clicked() {
var myDiv = $("#my-div");
$.post("someurl.php",someData,function(data){
doSomething(data, myDiv);
},"json");
}
function doSomething(curData, curDiv) {
}

You can use a closure of JavaScript:
function wrapper( var1, var2,....) // put here your variables
{
return function( data, status)
{
//Handle here results of call
}
};
and when you can do:
$.post("someurl.php",data,wrapper(var1, var2, etc...),"html");

I've made a mistake in the last my post. This is working example for how to pass additional argument in callback function:
function custom_func(p1,p2) {
$.post(AJAX_FILE_PATH,{op:'dosomething',p1:p1},
function(data){
return function(){
alert(data);
alert(p2);
}(data,p2)
}
);
return false;
}

Let's go simple ! :)
$.ajax({
url: myUrl,
context: $this, // $this == Current $element
success: function(data) {
$.proxy(publicMethods.update, this)(data); // this == Current $element
}
});

A more general solution for sending asynchronous requests using the .ajax() jQuery API and closures to pass additional parameters to the callback function:
function sendRequest(method, url, content, callback) {
// additional data for the callback
var request = {
method: method,
url: url
};
$.ajax({
type: method,
url: url,
data: content
}).done(function(data, status, xhr) {
if (callback) callback(xhr.status, data, request);
}).fail(function(xhr, status) {
if (callback) callback(xhr.status, xhr.response, request);
});
};

For me, and other newbies who has just contacted with Javascript,
I think that the Closeure Solution is a little kind of too confusing.
While I found that, you can easilly pass as many parameters as you want to every ajax callback using jquery.
Here are two easier solutions.
First one, which #zeroasterisk has mentioned above, example:
var $items = $('.some_class');
$.each($items, function(key, item){
var url = 'http://request_with_params' + $(item).html();
$.ajax({
selfDom : $(item),
selfData : 'here is my self defined data',
url : url,
dataType : 'json',
success : function(data, code, jqXHR){
// in $.ajax callbacks,
// [this] keyword references to the options you gived to $.ajax
// if you had not specified the context of $.ajax callbacks.
// see http://api.jquery.com/jquery.ajax/#jQuery-ajax-settings context
var $item = this.selfDom;
var selfdata = this.selfData;
$item.html( selfdata );
...
}
});
});
Second one, pass self-defined-datas by adding them into the XHR object
which exists in the whole ajax-request-response life span.
var $items = $('.some_class');
$.each($items, function(key, item){
var url = 'http://request_with_params' + $(item).html();
$.ajax({
url : url,
dataType : 'json',
beforeSend : function(XHR) {
// 为了便于回调，把当前的 jquery对象集存入本次 XHR
XHR.selfDom = $(item);
XHR.selfData = 'here is my self defined data';
},
success : function(data, code, jqXHR){
// jqXHR is a superset of the browser's native XHR object
var $item = jqXHR.selfDom;
var selfdata = jqXHR.selfData;
$item.html( selfdata );
...
}
});
});
As you can see these two solutions has a drawback that : you need write a little more code every time than just write:
$.get/post (url, data, successHandler);
Read more about $.ajax : http://api.jquery.com/jquery.ajax/

If someone still comes here, this is my take:
$('.selector').click(myCallbackFunction.bind({var1: 'hello', var2: 'world'}));
function myCallbackFunction(event) {
var passedArg1 = this.var1,
passedArg2 = this.var2
}
What happens here, after binding to the callback function, it will be available within the function as this.
This idea comes from how React uses the bind functionality.

$(document).on('click','[action=register]',function(){
registerSocket(registerJSON(),registerDone,second($(this)));
});
function registerSocket(dataFn,doneFn,second){
$.ajax({
type:'POST',
url: "http://localhost:8080/store/public/register",
contentType: "application/json; charset=utf-8",
dataType: "json",
data:dataFn
}).done ([doneFn,second])
.fail(function(err){
console.log("AJAX failed: " + JSON.stringify(err, null, 2));
});
}
function registerDone(data){
console.log(JSON.stringify(data));
}
function second(element){
console.log(element);
}
Secondary way :
function socketWithParam(url,dataFn,doneFn,param){
$.ajax({
type:'POST',
url:url,
contentType: "application/json; charset=utf-8",
headers: { 'Authorization': 'Bearer '+localStorage.getItem('jwt')},
data:dataFn
}).done(function(data){
doneFn(data,param);
})
.fail(function(err,status,xhr){
console.log("AJAX failed: " + JSON.stringify(err, null, 2));
});
}
$(document).on('click','[order-btn]',function(){
socketWithParam(url,fakeDataFn(),orderDetailDone,secondParam);
});
function orderDetailDone(data,param){
-- to do something --
}

actually, your code is not working because when you write:
$.post("someurl.php",someData,doSomething(data, myDiv),"json");
you place a function call as the third parameter rather than a function reference.

As an addendum to b01's answer, the second argument of $.proxy is often used to preserve the this reference. Additional arguments passed to $.proxy are partially applied to the function, pre-filling it with data. Note that any arguments $.post passes to the callback will be applied at the end, so doSomething should have those at the end of its argument list:
function clicked() {
var myDiv = $("#my-div");
var callback = $.proxy(doSomething, this, myDiv);
$.post("someurl.php",someData,callback,"json");
}
function doSomething(curDiv, curData) {
//"this" still refers to the same "this" as clicked()
var serverResponse = curData;
}
This approach also allows multiple arguments to be bound to the callback:
function clicked() {
var myDiv = $("#my-div");
var mySpan = $("#my-span");
var isActive = true;
var callback = $.proxy(doSomething, this, myDiv, mySpan, isActive);
$.post("someurl.php",someData,callback,"json");
}
function doSomething(curDiv, curSpan, curIsActive, curData) {
//"this" still refers to the same "this" as clicked()
var serverResponse = curData;
}