I'm trying to load JSON with a JS function, and then make the JSON objects that are loaded available to other functions in the same namespace. I've tried using return to serve up the array of objects retrieved, but that doesn't work. In the attached example, I've assigned the array of objects to a property in the namespaced object, but when I try to get that array of objects outside the main loadData function, all I get is null.
Here's my JS:
var myObj = {
jsonEndPoint: '/test/test.json',
dataObjects: null
}
myObj.loadData = function () {
$.ajax({
url: 'test.json',
type: 'POST',
dataType: 'json',
success: function (data) {
myObj.dataObjects = data.apiResults[0].league.season.draft.rounds[0].picks;
//console.log(myObj.dataObjects);
},
error: function (xhr, textStatus, errorThrown) {
console.log('Data Load Error: ' + textStatus);
}
});
}()
myObj.displayData = function() {
console.log(myObj.dataObjects)
}()
The full example can be seen here: http://zbl.me/test/index.html
The JSON file I'm loading is here: http://zbl.me/test/test.json
That is because JavaScript is asynchronous in nature — when you attempt to access the myObj.dataObjects in the myObj.displayData function, that object does not yet exist because the AJAX call has not been completed yet.
What you could do is that ensure that all functions that require newly added data from the AJAX call be run only when a .done() promise has been delivered from your AJAX call, by using $.when(). The logic is quite straightforward:
myObj.loadData() is now exclusively used to make the AJAX call. With regards to how we handle the done and fail events (which are previously .success() and .error() callbacks), we delegate that logic to the next function.
myObj.displayData() is now use to evaluate the promise returned by your AJAX call made with myObj.loadData(). You use $.when() to fetch the promise, and then simply chain .done() to deal with a successful call and .fail() to deal with the opposite :)
Here's your improved code:
var myObj = {
jsonEndPoint: '/test/test.json',
dataObjects: null
}
myObj.loadData = function () {
// We return the AJAX object so that we can evaluate the state later
// This is very simple :)
return $.ajax({
url: 'test.json',
type: 'POST',
dataType: 'json'
});
}()
myObj.displayData = function() {
// Instead of using the deprecated .success() and .error()
// ... we use .done() and .fail()
$.when(myObj.loadData).done(function(data) {
myObj.dataObjects = data.apiResults[0].league.season.draft.rounds[0].picks;
}).fail(function(xhr, textStatus, errorThrown) {
console.log('Data Load Error: ' + textStatus);
});
}()
If you are unsure, you can check the dummy code here: http://jsfiddle.net/teddyrised/5rbd2eqq/1/ I have used the built-in JSON response from JSfiddle to generate an artificial response, but the logic is exactly the same as yours.
Your displayData method is called even before the ajax is completed. So you either need to call displayData in the success callback of ajax or change the structure a bit so that its easy to call.
Why don't you instead do something like this
var myObj = {
jsonEndPoint: '/test/test.json',
dataObjects: null,
displayData: function() {
console.log(this.dataObjects);
},
loadData: function() {
$.ajax({
context: this,
url: 'test.json',
type: 'GET',
dataType: 'json',
success: function(data) {
this.dataObjects = data.apiResults[0].league.season.draft.rounds[0].picks;
console.log(myObj.dataObjects);
this.displayData();
},
error: function(xhr, textStatus, errorThrown) {
console.log('Data Load Error: ' + textStatus);
}
});
}
};
myObj.loadData();
Here is a demo
Related
Struggling to return a AJAX Result Variable back to JavaScript
Note that the $.ajax call below is synchronous (async: false).
Ajax Call
function getState(callback) {
$.ajax({
url: 'getSearchState.php',
data: { "state": callback },
type: 'GET',
async: false,
success: function(result){
alert(result);
},
error: function(result) {
alert(result);
}
});
}
Ajax PHP
<?php
// Database Setup and Query
while ($row = $xxxxx->fetch(PDO::FETCH_ASSOC)) {
$StateVal = $row['State'];
}
return $StateVal;
?>
Javascript Calling the Function
var URL = District.trim();
var StateURL = getState(URL);
It gets the URL vairable from the function just fine, but doesnt return anything.
Any help would be great!
There are problems with that code both client-side and server-side.
Client-side:
Your getState is never returning anything, so it's no surprise that you don't see anything other than undefined for StateURL.
Don't use synchronous ajax. It makes for horrible UX. But if you really, really want to keep using it, here's how you would:
function getState(state) {
var result; // <=== Where we'll put our result
$.ajax({
url: 'getSearchState.php',
data: {"state": state},
type: 'GET',
async: false,
success: function(data) {
// Remember the result;
result = data;
},
error: function() {
result = /*...whatever you want to use to signal an error */;
}
});
// Return the result
return result;
}
Note that I changed the name of the argument to state, since it's not a callback.
But again, don't use synchronous ajax. Instead, use a callback or promises.
Promise: $.ajax already returns a promise, so just return that directly:
function getState(state) {
var result; // <=== Where we'll put our result
$.ajax({
url: 'getSearchState.php',
data: {"state": state},
type: 'GET',
async: false,
success: function(data) {
// Remember the result;
result = data;
},
error: function() {
result = /*...whatever you want to use to signal an error */;
}
});
// Return the result
return result;
}
Note that I changed the name of the argument to state, since it's not a callback.
But again, don't use synchronous ajax. Instead, use a callback or promises.
Promise:
function getState(state) {
return $.ajax({
url: 'getSearchState.php',
data: {"state": state},
type: 'GET'
});
}
Usage:
getState(URL)
.done(function(StateURL) {
// Use it
})
.fail(function() {
// Failed
});
Callback:
function getState(state, callback) {
$.ajax({
url: 'getSearchState.php',
data: {"state": state},
type: 'GET',
success: function(data) {
// Call the callbback with the result
callback(data);
},
error: function() {
// Call the callback with an error
callback(/*...whatever you want to use tosignal an error */);
}
});
}
Usage:
getState(URL, function(StateURL) {
// Use it, check for error
});
Server-side:
As RiggsFolly pointed out, you're returning a string from your PHP code. But that won't output it. To use it client-side, you need to output it (e.g., echo and similar). And to make it easily consumed by the JavaScript, you probably want to json_encode it to ensure that it's in a format JavaScript can understand:
echo json_encode($stateVal);
Then in your success (or done) function, use JSON.parse on it:
result = JSON.parse(data);
this is jQuery and in this case you can specify context and in success function set variables on that context.... a bit crude solution but it will works. Also take a look on arrow functions and promises from ES6, it can help you a lot and give you new perspective about whole problem.
And one main thing!! Ajax is async by default so you need somehow notify your StateURL when data will be ready (here again promise at you service)
Even though i am able to pass promise as parameter into error function, it does not trigger then & error function on the caller.?
if i change the code to put the AJAXError function inline, everything works fine.
Is it possible to pass around the promise around as parameter and still be able to trigger back then and fail on the caller up in the chain.
NOTE : promise is returned from palletizerService.addSerialNumberToPallet but but resolved/rejected in a different function AjaxFailed.
palletizerService.addSerialNumberToPallet ('p1','s1')
.then( function (response){
console.log('success');
},
function(error){
console.error(error);
});
Hereunder is the service that i am invoking from the above code
palletizerService.addSerialNumberToPallet = function (palletID, serialNumber) {
var deferred = $q.defer();
$.ajax({
url: url,
type: "GET",
dataType: "json",
methodName: methodName,
deferred: deferred.promise,
data: "palletID=" + palletID + "&serialNumber=" + serialNumber,
timeout: 20000, // 20 seconds for getting result, otherwise error.
error: AjaxFailed,
complete: function (jqXHR, textStatus) {
console.log("Ajax-finally : " + methodName);
},
beforeSend: function (qXHR, settings) {
},
success: function (data, textStatus, jqXHR) {
console.log("Ajax-Sucess " + methodName);
deferred.resolve(data);
}
});
return deferred.promise;
};
This is the external function
function AjaxFailed(qXHR, textStatus, errorThrown) {
try {
console.error('Ajax-Error in ' + methodName, qXHR.status, qXHR.responseText);
} catch (e) {
console.log("LocalMethod-Error in " + methodName);
console.error(e);
}
finally {
this.deferred.reject(qXHR);
}
}
Your problem is that you are passing the promise as the .deferred property of your options object. You cannot resolve/reject promises, they don't have a .reject method (and your code should throw when trying to call it). You would instead need to pass the deferred object you are holding.
However, this is a bad idea anyway. As jQuery.ajax does already return a promise, you should simply assimilate it using $q.when:
function (palletID, serialNumber) {
return $q.when($.ajax({
…
}));
}
(you will be able to omit all success and errror handlers, angular-promise does take care of them; if you want to add transformations or logging do those on the promise).
Yet that's still not optimal, in fact there hardly is a reason to use jQuery.ajax at all. Just use Angular's $http service, which also returns an angular promise right away.
I have a set of custom user data that I want to make an ajax call to, and in the event that there is no user data, make another ajax call to retrieve a default set of data, and then execute a function after parsing the data. Here's an example:
var oData = [],
exampleUrl = 'example.php';
$.ajax({
url: exampleUrl + '?query=getUserData',
contentType: 'application/json;odata=verbose',
headers: {
'accept': 'application/json;odata=verbose'
},
success : function(data, request){
// Request succeeded
// Check the results
if(data.length){
// There are custom user results!
// Parse the results
oData = data;
}
else{
// There were no custom user results...
// Run another query to retrieve default values
$.ajax({
url: examplUrl + '?query=getDefaultData',
contentType: 'application/json;odata=verbose',
headers: {
'accept': 'application/json;odata=verbose'
},
success : function(data, request){
// Request succeeded
// Check the results
if(data.length){
// There was some default data!
// Parse the results
oData = data;
}
else{
// No data was found...
// Attempt to be helpful
console.log('No Default data was found!');
}
},
error : function(data, request){
// There was an error with the request
// Attempt to be helpful
console.log('Error retrieving data:');
console.log(data);
console.log(request);
}
});
}
},
error : function(data, request){
// There was an error with the request
// Attempt to be helpful
console.log('Error retrieving Custom User data:');
console.log(data);
console.log(request);
},
complete : function(){
// Do something with the data
index.displayData(oData);
}
});
The issue is that if the second ajax call is run, oData doesn't contain any data at all when it's passed to index.displayData(). I'm guessing it has something to do with the asyncronous nature of ajax calls, but shouldn't 'complete' run after everything inside of 'success' runs?
I also know I probably shouldn't be using the ajax "Pyramid of Doom" and should be using promises, but I've tried them and keep getting the same results.
Thank you for your assistance!
As pointed out by Violent Crayon, you could try calling "complete" yourself instead of relying on JQuery's implicit control flow:
function getData(exampleUrl, onComplete){
$.ajax({
success : function(data, request){
if(data.length){
onConplete(data);
}else{
$.ajax({
success : function(data, request){
if(data.length){
onComplete(data);
}else{
console.log('No Default data was found!');
}
},
error : function(data, request){
console.log('Error retrieving data:');
}
});
}
},
error : function(data, request){
console.log('Error retrieving Custom User data:');
}
});
}
var oData = [];
getData('example.php', function(data){
oData = data;
index.displayData(oData);
}
BTW, note how you can have your async functions receive their own return and error callbacks. This can help reduce the pyramid of doom problem without needing to use promises and without needing to hardcode the return callback.
By working with promises, you can avoid the need to pass a callback into your function, and by defining a utility function you can avoid repetition of code.
//reusable utility function, which returns either a resolved or a rejected promise
function fetchData(queryString, cache) {
return $.ajax({
url: 'example.php',
data: { query: queryString },
type: 'JSON',//assumed
cache: cache,
contentType: 'application/json;odata=verbose',
headers: { 'accept': 'application/json;odata=verbose' }
}).then(function(data, textStatus, jqXHR) {
if (data && data.length) {
return data;
} else {
return $.Deferred().reject(jqXHR, 'no data returned').promise();//emulate a jQuery ajax failure
}
});
}
This allows promise methods to be used for a control structure, which :
is concise
uses chaining, not nesting
gives meaningful error messages.
//control structure
fetchData('getUserData', false).then(null, function(jqXHR, textStatus) {
console.log('Error retrieving Custom User data: ' + textStatus);
return fetchData('getDefaultData', true);
}).then(index.displayData, function(jqXHR, textStatus) {
console.log('Error retrieving default data: ' + textStatus);
});
Notes :
the null in .then(null, function(){...}) allows a successful response to drop straight through to the second .then(index.displayData, ...)
default data is cached while the user data is not. This is not necessary to make things work but will be faster next time the default data is required.
in the world of promises, this or something similar is the way to go.
If I have to leverage niceties of jQuery AJAX API and set my own custom settings for each ajax call my app makes like below:
Say I have a page which displays employee information within table by making ajax calls to some API.
define(["jQuery"], function($) {
var infoTable = function (options) {
function init() {
// Provide success callback
options.success_callback = "renderData";
getData();
}
function renderData() {
// This callback function won't be called as it is not
// in global scope and instead $.ajax will try to look
// for function named 'renderData' in global scope.
// How do I pass callbacks defined within requirejs define blocks?
}
function getData() {
$.ajax({
url: options.apiURL,
dataType: options.format,
data: {
format: options.format,
APIKey: options.APIKey,
source: options.source,
sourceData: options.sourceData,
count: options.count,
authMode: options.authMode
},
method: options.method,
jsonpCallback: options.jsonpCallback,
success: options.success_callback,
error: options.error_callback,
timeout: options.timeout
});
}
}
return {
init: init
}
}
How do I achieve this?
I know we can use JSONP request as require calls but that restricts me to using jsonp, making GET requests and all other features $.ajax offers.
This example would let you either use a default success callback, or provide an override, using:
success: options.successCallback || renderData
(The example uses jsfiddle rest URLs - this fact is unimportant, and stripped out the data object to keep the example short)
define("mymodule", ["jquery"], function($) {
function renderData() {
console.log("inside callback");
}
function getData(options) {
$.ajax({
url: options.apiURL,
dataType: options.format,
method: options.method,
jsonpCallback: options.jsonpCallback,
success: options.successCallback || renderData,
error: null,
timeout: options.timeout
});
}
return {
getData: getData
}
});
require(["mymodule"], function(m) {
console.log(m, m.getData({
apiURL: "/echo/json/"
}));
console.log(m, m.getData({
successCallback: function() { console.log("outside callback"); },
apiURL: "/echo/json/"
}));
});
Would print:
GET http://fiddle.jshell.net/echo/json/ 200 OK 263ms
Object { getData=getData()} undefined
GET http://fiddle.jshell.net/echo/json/ 200 OK 160ms
Object { getData=getData()} undefined
inside callback
outside callback
I'm trying to trigger an action after a Javascript object has been created via an AJAX call. My object looks something like this:
function API(uid,accessToken){
$.ajax("path/to/file", {
type: "POST",
data: { user: uid, auth: accessToken },
dataType: "json",
success: function(jsonData) {
arrayname = jsonData[values]
}
});
}
I tried to use JQuery's $.when function to do a callback after the object setup is complete (ie. the array is populated with the ajax response), which looked like this:
$.when( API = new API(uid, accessToken) ).then(function() {
...success function...
});
...but the $.when function triggers with the arrayname values still undefined. From the function's standpoint the deferred object is resolved even though the object values have not yet been set. I've since tried a number of ways to make the API object become deferred based on the completing of the entire ajax call and the setting of the variables, but I'm a bit stuck on the best way to do this.
Any pointers would be most appreciated! Thanks.
You could pass the callback function when you create the object, like so:
function API(uid,accessToken, callback){
$.ajax("path/to/file", {
type: "POST",
data: { user: uid, auth: accessToken },
dataType: "json",
success: function(jsonData) {
arrayname = jsonData[values]
callback(jsonData[values])
}
});
}
and then instantiate the object like so
var api = new API(uid, accessToken, function(array) {
// success function
});
If the problem is due to the "success" callback running after the "then" callbacks, you could try turning success callback into a then callback as well. I don't use JQuery but I guess it would look something like:
function API(uid,accessToken){
return $.ajax("path/to/file", {
type: "POST",
data: { user: uid, auth: accessToken },
dataType: "json",
}).then(function(jsondata){
arrayname = jsondata[values]
});
}
$.when( API = new API(uid, accessToken) ).then(function() {
// ...
});
The reason you use $.when is when you are correlating the callbacks of multiple promises, async tasks, etc. Since jQuery 1.5, all calls to $.ajax and all the wrappers ($.get and $.post) all return promises. Therefore you don't need to wrap this call with the $.when statement unless you want to do $.when(ajaxCall1, ajaxCall2).
Since you want to filter the result from the server, you should use the pipe method of promises:
function API(uid, accessToken)
return $.post(
type: 'POST'
,data: { user: uid, auth: accessToken }
,dataType: 'json'
)
.pipe(function(json) {
return json[values];
})
;
}
This allows you to write your code the way you desire:
API(uid, token)
.then(
// success state (same as promise.done)
function(arrayname /* named from your sample script*/) {
alert('success! ' + arrayname);
}
// error state (same as promise.fail)
,function(jqXHR, status, error) {
console.warn('oh noes!', error);
}
)
.done(function() { /* done #2 */ })
.fail(function() { /* fail #2 */ })
;
Note: promise.pipe() also allows you to filter (change the data passed to) the error callback as well.