Develop Reference

How to get a JSON string result from a database for later use

I am working on the backend for a webpage that displays EPG information for TV channels from a SQlite3 database. The data is provided by a PHP script echoing a JSON string. This itself works, executing the php program manually creates a JSON string of this format
[{"id":"0001","name":"RTL","frequency":"626000000"},{"id":...
I want to use these objects later to create HTML elements but the ajax function to get the string doesn't work. I have looked at multiple examples and tutorials but they all seemed to be focused more on having PHP return self contained HTML elements. The relevant js on my page is this:
var channelList;
$(document).ready(function() {
$.ajax({
url: 'channellookup.php',
dataType: "json",
success: function(data) {
console.log(data.success);
channelList = data;
}
});
});
However the channelList variable remains empty when inspected via console.
What am I doing wrong?

Please ensure that your PHP echoing the correct type of content.
To echo the JSON, please add the content-type in response header.
<?php
header(‘Content-type:text/json’); // To ensure output json type.
echo $your_json;
?>

It's because the variable is empty when the program runs. It is only populated once AJAX runs, and isn't updating the DOM when the variable is updated. You should use a callback and pass in the data from success() and use it where you need to.
Wrap the AJAX call in a function with a callback argument. Something like this:
function getChannels(callback){
$.ajax({
url: 'channellookup.php',
dataType: "json",
success: function(data) {
console.log(data);
if (typeof(callback) === 'function') {
callback(data);
}
},
error: function(data) {
if (typeof(callback) === 'function') {
callback(data);
}
}
});
}
Then use it when it becomes available. You should also use error() to help debug and it will quickly tell you if the error is on the client or server. This is slightly verbose because I'm checking to make sure callback is a function, but it's good practice to always check and fail gracefully.
getChannels(function(channels){
$('.channelDiv').html(channels.name);
$('.channelDiv2').html(channels.someOtherProperty);
});
I didn't test this, but this is how the flow should go. This SO post may be helpful.
EDIT: This is why frameworks like Angular are great, because you can quickly set watchers that will handle updating for you.

Get AJAX data from server before document ready (jQuery)

I want take some data from server and write it to global array in JavaScript. Then in document ready I want to use this array to create some new elements (options). I should have global array with this data, because after first load client can modify user interface using this data.
$(document).ready(function () {
UseAjaxQueryForFillGlobalArray();
MakingInterfaceUsingGlobalArray();
});
But I have strange behavior, when I debug page, I can see that method MakingInterfaceUsingGlobalArray working first, and just after I get data via AJAX with method UseAjaxQueryForFillGlobalArray and I don't have new interface(html options) with loaded data.
If I do like this:
UseAjaxQueryForFillGlobalArray();
$(document).ready(function () {
MakingInterfaceUsingGlobalArray();
});
Then in Firefox working fine, but in another web-browsers incorrect in first load (for example go to this page by link). But if I refreshing by F5, I have correct user interface which loaded via AJAX to global JS array.
How to fix it? Maybe I using totally incorrect way?
Added after comments:
This is my ajax function:
function UseAjaxQueryForFillGlobalArray(){
var curUserId = '<%= Master.CurrentUserDetails.Id %>';
var curLocale = '<%= Master.CurrentLocale %>';
$.ajax({
type: "POST",
url: "/segment.aspx/GetArrayForCF",
data: '{"userId":"' + curUserId + '","curLocale":"' + curLocale + '"}',
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function (msg) {
//here is I doing parse my string from server and fill arrays.
}
});
}

I think that the problem is that you don't know exactly when the first function returns, since it'a asynchronous. So you should use the array in the callback only
function UseAjaxQueryForFillGlobalArray() {
// make the call
$.post(url, data, function() {
// let's be sure that the dom is ready
$(document).ready(function () {
// use the array
MakingInterfaceUsingGlobalArray();
}
}
}();// invoke the function

It's like reviving this post from the dead, but I had the same problem today, jQuery version greater than 1.6 has this ability:
https://api.jquery.com/jquery.holdready/
And I've used it like this:
$.holdReady(true);
var remoteJSONContent = null;
$.getJSON("http://www.example.com/remote.json", function(data) {
remoteJSONContent = data;
$.holdReady(false);
});
$(document).ready(function(){
console.log(remoteJSONContent);
});
Without using holdReady, I was getting null, after, I got the content.
For anyone still searching the answer for this.

Rendering mongodb database results from POST request in .ajax jquery wrapper in node js

I am creating a basic piece of functionality to allow users to send their location to a server which then queries a database and returns locations near to them. I am using the below jQuery .ajax wrapper to POST data to the server. This takes the form of a latlon point which is then used as the basis for a geosearch in MongoDB using nodejs and express on the backend. The results of the search are then intended to be returned to the client and rendered by the createMapListings function.
The /find page is initially rendered through a GET request to the database via mongodb separate from the below code. However subsequent to initial rendering, I then want to return results dependent on the location provided.
The POST method works fine and the location is posted to the server, with the search results being returned as I can print contents out through the console log.
However, I then want to render the results on the client-side. As mentioned, the results of the search render in the console, but when I attempt to pass through to the client, I can render the data itself (in the form of an array of objects) in the #output div, but the createMapListings function does not seem to catch the data.
In fact, the below function appears to be called but prints out over a thousand rows with the data that should be caught described as 'undefined'. I have tried to use res.render and res.redirect, but in the first case, the view renders in the div (which I suppose is expected) and the redirect fails.
The createMapListings function works fine when a simple GET request is made to the server, for example, for all objects in a collection, using ejs template. However, I think the issue here may be a combination of a POST request and then wanting to pass the results back to the AJAX request using the complete callback.
I apologise if the below code is somewhat obtuse. I’m definitely what you would call a beginner. I appreciate the above functionality may not possible so if there is a better way, I would of course be open to it (res.direct perhaps).
Here is the relevant client side script:
$(document).ready(function(){
$("#geolocate").click(function(){
navigator.geolocation.getCurrentPosition(geolocate, function(){
});
});
});
function geolocate(pos){
var latlonpt = [];
var x = pos.coords.latitude;
var y = pos.coords.longitude;
latlonpt.push(x);
latlonpt.push(y);
var obj = {
userlocation: latitudelongitudept
};
$.ajax({
url: "/find",
type: "POST",
contentType: "application/json",
processData: false,
data: JSON.stringify(obj),
complete: function (data) {
$('#output').html(data.responseText);
$('#infooutput').children().remove();
createMapListings(data.responseText);
}
});
};
function createMapListings(maps) {
for (var i = 0; i < maps.length; i++) {
var url = maps[i]._id;
var fullurl = "<a href='/show?id=" + url + "'>Route</a></div>";
var title = "<div>" + maps[i].title + " - " + fullurl +"";
$('#infooutput').append(title);
};
};
</script>
Here is the relevant route used in a basic express app to handle the post request made by the above .ajax wrapper.
exports.findbylocation = function(req, res) {
console.log(req.body.userlocation);
var userlocation = req.body.userlocation;
Map.ensureIndexes;
Map.find({loc :{ $near : userlocation }}, function(err, maps) {
if (err) {
console.log(err)
}
else {
var jmaps = JSON.stringify(maps);
console.log(jmaps);
res.send(jmaps);
}
});
};

By convention, the data variable name in an $.ajax callback signature refers to the parsed HTTP response body. Since your callback is on complete, we're actually passed the XMLHttpRequest used, by convention called xhr. You rightly grab the responseText property, but this needs parsing to be useful. So long as we take care over our Content-Type's and don't explicitly disable processData, jQuery will do the encoding/unencoding for us - we just deal with objects. This is a good thing, since the transport format isn't usually of any particular importance to the application logic. If we use res.json(maps) in place of res.send(jmaps), we can write our call more simply:
$.ajax({
url: '/find',
type: 'POST',
data: obj,
success: function(data) {},
error: function(xhr, text, err) {}
});
Here data is a Javascript object already parsed and ready to use. We also use a default application/x-www-form-urlencoded request rather than explicitly setting a contentType. This is the same as far as express is concerned: it will just be parsed by urlencoded instead of json.

Assuming you solved your client-sie problem.
As you are using express there is no need for JSON.stringfy,
you can use res.json(maps).

prevent jquery ajax to execute javascript from script or html response

According to documentation:
If html is specified, any embedded JavaScript inside the retrieved
data is executed before the HTML is returned as a string. Similarly,
script will execute the JavaScript that is pulled back from the
server, then return nothing.
How to prevent this?
I have js that shall modify the content that is obtained through ajax. Executing it before the html is returned makes no sense as it does not have content to work on (at least in my case).
my code:
function do_ajax(url) {
$.ajax({
cache: false,
url : url,
success: function(response, status, xhr) {
var ct = xhr.getResponseHeader("content-type") || "";
if (ct.indexOf('script') > -1) {
try {
eval(response);
}
catch(error) {}
} else {
var edit_dialog = $('<div class="edit_dialog" style="display:hidden"></div>').appendTo('body');
edit_dialog.html(response);
edit_dialog.dialog({ modal:true, close: function(event, ui) { $(this).dialog('destroy').remove(); } });
}
},
error: function (xhr, ajaxOptions, thrownError) {
alert(xhr.status);
alert(thrownError);
}
});
}
the script received by ajax is executed twice. First by me in the eval(response), then jquery execute it again (as described in the documentation)

Lee's answer already adequately addresses the case of HTML responses - scripts embedded in these are not in fact executed automatically unless you add the HTML to the DOM, contrary to the erroneous documentation you quoted.
That leaves the other case asked about in your question title - preventing script responses from being executed automatically when received. You can do this easily using the dataType setting.
$.ajax('myscript.js', {
dataType: 'text',
success: function (response) {
// Do something with the response
}
})
Setting dataType to 'text' will cause jQuery to disregard the Content-Type header returned from the server and treat the response like plain text, thus preventing the default behaviour for JavaScript responses (which is to execute them). From the (recently corrected) docs:
The type of pre-processing depends by default upon the Content-Type of the response, but can be set explicitly using the dataType option. If the dataType option is provided, the Content-Type header of the response will be disregarded.
...
If text or html is specified, no pre-processing occurs. The data is simply passed on to the success handler, and made available through the responseText property of the jqXHR object.

jQuery.ajax does not evaluate scripts on return when requesting HTML. The passage you quoted in the question was in fact a long-standing error in the documentation, fixed as of April 2014. The new docs have this to say (emphasis mine):
"html": Returns HTML as plain text; included script tags are evaluated when inserted in the DOM.
...
If text or html is specified, no pre-processing occurs. The data is simply passed on to the success handler, and made available through the responseText property of the jqXHR object.
The scripts are evaluated in this case when you call
edit_dialog.html(response);
If you don't want to evaluate the scripts before inserting your response in to the DOM, you should be able to do something like:
edit_dialog.html($($.parseHTML(response)));
parseHTML is the key in that by default it removes script tags. However, be aware that parseHTML is NOT XXS safe and if your source is unknown this is still a security concern.

The documentation states that any embedded Javascript inside the retrieved data will be executed before the HTML is returned as a string. If you want to then alter whatever you have retrieved using your ajax call, you can do so within the succes property:
$.ajax({
url: "example.html",
type: "GET",
dataType: "html",
succes: function(data){
// Example: alert(data);
// Do whatever you want with the returned data using JS or jQuery methods
}
});

That's one of the really annoying things about jQuery that it executes javascript on response.
Other frameworks like MooTools disable script execution from responses unless you specifically set that you want them executed which is a much better approach.
The only way I could figure to prevent scripts being executed is to add a custom dataFilter
Its easy enough but I think it should be default and an ajax option to enable script execution if you want it (I've never had a use for it and other frameworks disable by default for security etc.)
Example
$.ajax('uri',{
dataFilter: function(data, type)
{
type = type || 'text';
if(type=='html'||type=='text'){
/*return data.replace(/<script.*>.*?<\/script>/gi, '');*/
return data.replace(/<script.*?>([\w\W\d\D\s\S\0\n\f\r\t\v\b\B]*?)<\/script>/gi, '');
}
return data;
}
, success: function(data)
{
// whatever
}
});
** UPDATED **
Needs that crazy regex to cover more script tag instances
NOTE
if dataType hasnt been set in options it will be undefined in dataFilter so I just default it to text for the filter - if you remove that line then it will only work if dataType is explicitly set.

Using Javascript / JQuery to access an array built from an external XML file

I hope this is not too much of a newbe question but I've been pulling my hair out for a while now so thought I'd give in and ask for my first piece of advice on here.
I'm trying to read an external xml file using javascript / jQuery / ajax and place the retrieved data into an array so that I can then reference it later.
So far I seem to be doing everything right upto the point I put the data into the array but then I'm struggling to to read the data anywhere other than inside the function where I create it. Why am I not able to access the Array from anywhere other than in that function?
Here is my code...
Please help!!
$.ajax({
type: "GET",
url: "data.xml",
dataType: "xml",
success: do_xmlParser
});
function do_xmlParser(xml)
{
var myArray = new Array();
$(xml).find("tag").each(function ()
{
myArray.push($(this).find("innerTag").text());
});
console.log("inside "+myArray); // This outputs the array I am expecting
return myArray; // is this right???
}
console.log("outside: "+myArray); // This does NOT output the array but instead I get "myArray is not defined"

You're defining do_xmlParser as a callback to an asynchronous function (success of the jquery ajax call). Anything you want to happen after the ajax call succeeds has to occur within that callback function, or you have to chain functions from the success callback.
The way you have it now, the actual execution of code will go:
ajax -> file being requested -> console.log ->
file transfer done -> success handler
If you're doing some critical stuff and you want the call be to synchronous, you can supply the
async : false
setting to the ajax call. Then, you should be able to do something like this:
var myArray = [],
do_xmlParser = function (xml)
{
$(xml).find("tag").each(function ()
{
myArray.push($(this).find("innerTag").text());
});
};
$.ajax({
type: "GET",
url: "data.xml",
dataType: "xml",
success: do_xmlParser,
async: false
});
console.log("outside: " + myArray);
The async option doesn't work for cross-domain requests, though.
NOTE
I don't recommend doing this. AJAX calls are supposed to be asynchronous, and I always use the success callback to perform all of the processing on the returned data.
Edit:
Also, if you're into reading... I'd recommend jQuery Pocket Reference and JavaScript: The Definitive Guide (both by David Flanagan).

look close and you will see. You are actually firing up an array that dosen't exist. You have declared myArray inside function. Try do something like this.
console.lod("outside :"+do_xmlParser(xml)); // I think that when you merge a string and an array it will output only string, but I can be wrong.