I tried to use this loop to read some urls to read their modified time:
var arr = [];
//... fill arr with push
for (var e in arr) {
nodename=arr[e].hostname;
node_json="/nodes/"+nodename;
html +='data';
xhr = $.ajax({
url: node_json,
success: (function(nn) {
$('#host_'+nn).append("last modified: " + xhr.getResponseHeader("Last-Modified"));
})(nodename)
});
This already works a bit i I comment out the success line: I get calls to all node-files, and in Firebug, I can see the different modified times in the header of the calls.
At first I had a closure, (see How to generate event handlers with loop in Javascript?) And I only got the last line modified with all results. that's why I try to put the action in a separate function.
But that gives:
ReferenceError: xhr is not defined
$('#host_'+nn).append("last modified: " + xhr.getResponseHeader("Last-Modified")...
How do I get xhr into that function?
I aslo tried:
...
xhr[e] = $.ajax({
url: node_json,
success: add_result_to_info(nodename, e)
});
}
}
// outside loop
function add_result_to_info(nn, e) {
$('#host_'+nn).append("last modified: " + xhr[e].getResponseHeader("Last-Modified"));
}
source of the AJAX call: Get the modified timestamp of a file with javascript
If arr is truly an array, just use .forEach or even better .map (with a shim on older browsers) to encapsulate each iteration's scope without the need for additional closures:
var xhrs = arr.map(function(e) {
var nodename = e.hostname;
var node_json = "/nodes/" + nodename;
html +='data';
return $.ajax({
url: node_json
}).done(function(data, status, xhr) {
$('#host_'+nodename).append("last modified: " + xhr.getResponseHeader("Last-Modified"));
});
});
The reason to use var xhrs = arr.map() instead of .forEach is that you then (for free) get the ability to call yet another callback once every AJAX request has completed:
$.when.apply($, xhrs).then(function() {
// woot! They all finished
...
});
your are directly executing the method and passing its result as the callback for the success callback.
the xhr is already passed as the 3rd argument so try
success: function(nn,status, xhr) {
$('#host_'+nn).append("last modified: " + xhr.getResponseHeader("Last-Modified"));
}
if you have to pass the nodename as well, the you need to use a function that returns a function
success: (function(nn){
return function(data ,status, xhr) {
// you can use nodename here...
$('#host_'+nn).append("last modified: " + xhr.getResponseHeader("Last-Modified"));
};
})(nodename)
Related
I have a general ajax function which I'm calling from loads of places in my code. It's pretty standard except for some extra debugging stuff I've recently added (to try to solve this issue), with a global 'ajaxworking' variable:
rideData.myAjax = function (url, type, data, successfunc) {
var dataJson = JSON.stringify(data),
thisurl = quilkinUrlBase() + url;
if (ajaxworking.length > 0) {
console.log(thisurl + ": concurrent Ajax call with: " + ajaxworking);
}
ajaxworking = thisurl;
$.ajax({
type: type,
data: dataJson,
url: thisurl,
contentType: "application/json; charset=utf-8",
dataType: "json",
async: true,
success: function (response) {
ajaxworking = '';
successfunc(response);
},
error: webRequestFailed
});
};
Now, there's one section of my code where a second ajax call is made depending on the result of the first:
getWebRides = function (date) {
var rideIDs = [];
var intdays = bleTime.toIntDays(date);
rideData.myAjax("GetRidesForDate", "POST", intdays, function (response) {
rides = response;
if (rides.length === 0) {
$('#ridelist').empty(); // this will also remove any handlers
qPopup.Alert("No rides found for " + bleTime.DateString(date));
return null;
}
$.each(rides, function (index) {
rideIDs.push(rides[index].rideID);
});
GetParticipants(rideIDs);
});
},
'GetParticipants' (which also calls 'myAjax') works fine - most of the time. But in another part of my code, 'GetWebRides' is itself called directly after another ajax call - i.e. there are 3 calls, each successive one depending on the previous. The 'top-level' call is as follows:
rideData.myAjax("SaveRide", "POST", ride, function (response) {
// if successful, response should be just a new ID
if (response.length < 5) {
// document re-arrangement code snipped here for brevity
getWebRides(date);
}
else {
qPopup.Alert(response);
}
});
so, only when there are three successive calls like this, I'm getting the 'concurrent' catch in the third one:
GetParticipants: concurrent call with GetRidesForDate
and (if allowed to proceed) this causes a nasty probem at the server with datareaders already being open. But why is this only occurring when GetParticipants is called as the third in the chain?
I see, after some research. that there are now other ways of arranging async calls, e.g. using 'Promises', but I'd like to understand what's going on here.
Solved this.
Part of the 'document re-arrangement code' that I had commented out for this post, was in fact calling another Ajax call indirectly (very indirectly, hence it took a long time to find).
I've read a good bit about callbacks, and while I use them for click events and similar, I'm using them without fully understanding them.
I have a simple web app with 3 or 4 html pages, each with its own js page.
I have some global functions that I've placed in a new js page which is referenced by each html page that needs it. I'm using this file, word_background.js, to hold functions that are lengthy and used by multiple pages.
pullLibrary is a function, residing in word_background.js, that pulls from my db and processes the results.
I want to call pullLibrary from webpageOne.html, make sure it completes, then do more processing in webpageOne.js.
In webpageOne.js I have the following - trying to call pullLibrary and, once it is complete, use the results for further work in webpageOne.js.
The code executes pullLibrary (in word_background.js) but doesn't "return" to webpageOne.js to continue processing.
I'm assuming I'm missing some critical, essential aspect to callbacks...
I just want to run the pullLibrary function (which has ajax calls etc) and, once it is complete, continue with my page setup.
Any explanation/correction appreciated.
This code is in webpageOne.js:
pullLibrary(function(){
console.log('Now processing library...');
processLibrary();
updateArrays();
//Do a bunch more stuff
});
----- UPDATE -----
Thank you for the comments...which I think are illuminating my broken mental model for how this should work.
pullLibrary is an ajax function - it pulls from a database and stuffs the results into an array and localStorage.
My expectation is that I can call pullLibrary and, when it is complete, the callback code (in this case anonymous function) will run.
function pullLibrary(){ //Values passed from startup() if no data is local
//Pull data from database and create basic LIBRARY array for further processing in processLibrary sub
console.log("Starting to pull library array in background.js..." + "User: " + localStorage.userID + " License: " + localStorage.licType);
var url1 = baseURL + 'accessComments3.php';
var url2 = '&UserID=' + localStorage.userID + '&LicType=' + localStorage.licType;
//Need global index to produce unique IDs
var idIndex = 0;
var index = 0;
$.ajax({
type: "POST",
url: url1,
data: url2,
// dataType: 'text',
dataType: 'json',
success: function(result){
// success: function(responseJSON){
arrLibrary = result; //store for use on this page
localStorage.library = JSON.stringify(result); //Store for use elsewhere
console.log('Saving to global variable: ') + console.log(arrLibrary);
//Now mark last update to both sync storage and local storage so access from other browsers will know to pull data from server or just use local arrays (to save resources)
var timeStamp = Date.now();
var temp = {};
temp['lastSave'] = timeStamp;
// chrome.storage.sync.set(temp, function() {
console.log('Settings saved');
localStorage.lastSync = timeStamp;
console.log('Last update: ' + localStorage.lastSync);
//Store Group List
var arrComGroups = $.map(arrLibrary, function(g){return g.commentGroup});
// console.log('List of comment groups array: ') + console.log(arrComGroups);
arrComGroups = jQuery.unique( arrComGroups ); //remove dupes
// console.log('Unique comment groups array: ') + console.log(arrComGroups);
localStorage.groupList = JSON.stringify(arrComGroups); //Store list of Comment Groups
//Create individual arrays for each Comment Groups
$.each(arrComGroups,function(i,gName){ //Cycle through each group of Comments
var arrTempGroup = []; //to hold an array for one comment group
arrTempGroup = $.grep(arrLibrary, function (row, i){
return row.commentGroup == gName;
});
//Store string version of each Comment Array
window.localStorage['group_' + gName] = JSON.stringify(arrTempGroup);
console.log('Creating context menu GROUPS: ' + gName);
});
// processLibrary(arrLibrary); //We've pulled the array with all comments - now hand off to processor
}, //End Success
error: function(xhr, status, error) {
alert("Unable to load your library from 11trees' server. Check your internet connection?");
// var err = eval("(" + xhr.responseText + ")");
// console.log('Error message: ' + err.Message);
}
}); //End ajax
}
Okay, there are tons of "here's how callbacks work" posts all over the internet...but I could never get a crystal clear example for the simplest of cases.
Is the following accurate?
We have two javascript files, one.js and two.js.
In one.js we have a function - lets call it apple() - that includes an Ajax call.
two.js does a lot of processing and listening to a particular html page. It needs data from the apple() ajax call. Other pages are going to use apple(), also, so we don't want to just put it in two.js.
Here's how I now understand callbacks:
one.js:
function apple(callback_function_name){
$.ajax({
type: "POST",
url: url1,
data: url2,
dataType: 'json',
success: function(result){
//apple processing of result
callback_function_name(); //This is the important part - whatever function was passed from two.js
}, //End Success
error: function(xhr, status, error) {
}
}); //End ajax
} //End apple function
** two.js **
This js file has all kinds of listeners etc.
$(document).ready(function () {
apple(function(apple_callback){
//all kinds of stuff that depends on the ajax call completing
//note that we've passed "apple_callback" as the function callback name...which is stored in the apple function as "callback_function_name".
//When the ajax call is successful, the callback - in this case, the function in two.js, will be called back...and the additional code will run
//So the function apple can be called by all sorts of other functions...as long as they include a function name that is passed. Like apple(anothercallback){} and apple(thirdcallback){}
}); //End apple function
}); //End Document.Ready
I am trying to get a specific piece of data from from a json source. I have declared a global variable and try to update the global variable but it doesn't update correctly. Also, the order in which my debug alerts run is confusing.
<script>
//global variable
var latestDoorStatus = "initialized value"; //set value for debugging purposes
//debug alert which also calls the function
alert("Alert#1: call getDoorStatus = " + getDoorStatus("***********"));
function getDoorStatus(public_key) {
//get data in json form
var cloud_url = 'https://data.sparkfun.com/output/';
// JSONP request
var jsonData = $.ajax({
url: cloud_url + public_key + '.json',
data: {page: 1},
dataType: 'jsonp',
}).done(function (results) {
var latest = results[0];
//debug alert
alert("Alert #2: latestDoorStatus = " + latestDoorStatus);
//update the global variable
latestDoorStatus = latest.doorstatus;
//debug alert
alert("Alert #3: latestDoorStatus = " + latestDoorStatus);
//return the global variable
return latestDoorStatus;
});
alert("Alert #4: latestDoorStatus = " + latestDoorStatus);
}
</script>
When I run this in my browser I get the following behaviors:
First I get alert#4 (supposed to run at END of the script) with the initialized value of the global variable
then I get alert#1 as "undefined". This is supposed to be the result of calling the function getDoorStatus which should return an updated value of latestDoorStatus
then I get alert #2 as the initialized value of latestDoorStatus which makes sense since the global variable has not yet been updated
then I get alert #3 with the correct value of latestDoorStatus
The function is supposed to return the variable latestDoorStatus AFTER alert #3 (i.e. after global variable has been updated correctly) so I don't understand why alert #1 (which is supposed to have the returned value) is coming back undefined and why alert#4 which is supposed to run at the very end of the script is running first.
You are calling $.ajax asynchronously, and passing a callback function to done.
function makeRequest() {
$.ajax({ // An async Ajax call.
url: cloud_url + public_key + '.json',
data: {page: 1},
dataType: 'jsonp',
}).done(function (results) {
// this code is executed only after the request to cloud_url is finished.
console.log("I print second.");
});
console.log("I print first.");
}
The callback is called when the request is finished, and when depends entirely on how long the request to https://data.sparkfun.com/output/ takes. So the code after your Ajax call is executed immediately, we're not waiting for the http request to finish.
Your function getDoorStatus returns nothing, but your callback passed to done does. The thing you need to know is that you can't return anything from asynchronously executed functions. Well, you can return, but there will be nothing there to use the returned value.
So instead, do the things you want to do with the returned data from https://data.sparkfun.com/output/ in the callback passed to done.
function getDoorStatus(public_key) {
//get data in json form
var cloud_url = 'https://data.sparkfun.com/output/';
// JSONP request
var jsonData = $.ajax({
url: cloud_url + public_key + '.json',
data: {page: 1},
dataType: 'jsonp',
}).done(function (results) {
// latestDoorStatus = results[0]; // Not a good practice.
// Instead:
showDoorStatus(results[0]);
});
}
function showDoorStatus(status) {
document.getElementById("door-status").innerText = status;
// Or something like this.
}
getDoorStatus("***********");
And somewhere in your HTML:
<p id="door-status"></p>
.done() will be called after the response of the AJAX request got received!
1) getDoorStatus() is called from inside alert() at top of code => #4 shown. It does not matter that the function is defined below and not above.
2) alert() at top of code is called & getDoorStatus() does not directly return a value => #1 shown with undefined.
3) AJAX response returned, .done() function gets called => #2 and #3 are shown.
I'm having trouble getting my information into an array in an ajax call, if I alert the information right after I insert it into the array it works fine, but if I do it at the end it alerts unidentified. I made sure that books is declared outside so it doesn't interfere.
var books = [];
$.ajax({
url: 'getFolderContents.php',
dataType: 'json',
success: function (data)
{
for(var i=0;i<data.length;i++) {
var amm = 0;
if(data[i].indexOf(".epub") !== -1) {
//$('#bTable').append("<td><a id = '" + data[i] + "' href = 'book.html'><img src = 'book.png' width = '100px'/><br/>" + data[i] + "</a></td>");
books.push(data[i]);
//alert(books[0]) Works if I call it from here, but not at the end.
}
}
},
error: function()
{
alert("error");
}
});
alert(books[0]);
Your
alert(books[0]);
will be executed while the Ajax call is running and therefore will not have any elements at this point of execution yet. Ajax is asynchronous - while you are doing a request to your PHP script your script continues execution.
Put all actions with books in your success function.
Another hint: As of jQuery version 1.8 you cannot longer use the parameter async: false to create a synchronous "A"jax call. You have to use the callback functions. Have a look at the docs for $.ajax
Your array hasn't lost any data; the data hasn't been put in there yet. The 'A' stands for "asynchronous", meaning your success callback hasn't run yet at the time you call the alert.
Put the alert inside your callback instead:
success: function (data)
{
for(var i=0;i<data.length;i++) {
var amm = 0;
if(data[i].indexOf(".epub") !== -1) {
//$('#bTable').append("<td><a id = '" + data[i] + "' href = 'book.html'><img src = 'book.png' width = '100px'/><br/>" + data[i] + "</a></td>");
books.push(data[i]);
//alert(books[0]) Works if I call it from here, but not at the end.
}
}
alert(books[0]);
},
Your alert is executing before the success function is called. Perhaps seeing the same code using a promise will make things clearer.
$.ajax( url: 'getFolderContents.php', dataType: "json" )
//the then function's first argument is the success handler
.then(function( data ) {
for(var i=0;i<data.length;i++) {
var amm = 0;
if(data[i].indexOf(".epub") !== -1) {
//$('#bTable').append("<td><a id = '" + data[i] + "' href = 'book.html'><img src = 'book.png' width = '100px'/><br/>" + data[i] + "</a></td>");
books.push(data[i]);
//alert(books[0]) Works if I call it from here, but not at the end.
}
alert(books[0]
});
});
I always feel this syntax makes async stuff make more sense. Otherwise this code functions exactly like Blazemonger's correct answer.
Your AJAX call is asynchronous, that's why it is undefined.
The alert at the end happens before the ajax success callback, because ajax is asynchronous.
I need to return dynamic loaded content. I thought this was the way to do it, but the function returns blank. What do I need to do in order to set htmlCode with the html code retrieved from jQuery.ajax?
// Get directory listing
function getHTML(instance, current_path, dir) {
var htmlCode = '';
jQuery.ajax({
type: "POST",
url: "../wp-content/plugins/wp-filebrowser/jquery.php",
dataType: 'html',
data: {instance: instance, current_path: current_path, dir: dir},
success: function(html){
htmlCode = html;
},
error: function(e) {
htmlCode = '[Error] ' + e;
}
});
return htmlCode;
}
This is happening because the ajax request takes some time to get the html and your return statement fires before the html is ready. Javascript code execution does not wait for your html to return. You can actually see this by removing the return and putting two alerts. Put one alert inside the success event and one where you have put your return statement. The second alert would alert before. So, even though your html is fetched, it is never actually returned successfully to the calling function because the return statement already fired by the time html is ready.
You can use a callback if you strictly want the function getHtml() to return (well actually call back) the html as an output, or else you can use the way suggested by Nick.
Here is how to use a callback:-
function getHTML(instance, current_path, dir,callback)
{
var htmlCode = '';
jQuery.ajax({
type: "POST",
url: "../wp-content/plugins/wp-filebrowser/jquery.php",
dataType: 'html',
data: {instance: instance, current_path: current_path, dir: dir},
success: function(html){
callback(html); //instead of a return
},
error: function(e) {
htmlCode = '[Error] ' + e;
}
});
}
Call the function like this -
getHTML(instance, current_path, dir,
function(html)
{
//Write code to use the html here - this will run when the getHTML() function does callback with the output html
}
);
Note the callback parameter in the function definition getHTML(instance, current_path, dir,callback) and the corresponding function(html){} part in the called function.
This way, you actually define:-
the called function to call back the caller function when the output is ready
and the caller function to do something when it receives the call back.
It's an asynchronous operation, so you can't really return like this...not without making the request synchronous (async: true option), but I advise against this...since it locks up the browser for the duration of the request. You can't return because the success callback, when asynchronous, doesn't happen until later after the request runs, so your htmlCode = html; code simply hasn't run yet.
It's a better approach to call what's needed from your success callback once you have the data ready, for example:
success: function(html){
doSomethingWithHtml(html);
},
or more succinctly for that specific one-liner case:
success: doSomethingWithHtml,