jQuery AJAX request to remote API blocked - javascript

I have been successfully accessing data from an external weather data service API for some time now using PHP cURL. Sometimes it takes a few seconds, sometimes up to 15 seconds for this web service to process my request. Therefore, I would like to perform this operation asynchronously.
I am trying jQuery AJAX to send this GET request now. However, it keeps throwing the following error:
"No Access-Control-Allow-Origin header is present on the requested resource".
I'm aware of the "same origin policy" restrictions, and have been researching it extensively here on stackoverflow and the jQuery docs. The docs say that JSONP requests are not subject to this restriction. When I try to designate JSONP as the dataType, I get an "unexpected token" syntax error.
I have the user entering in their zip code into a form text box, then click the button to submit. This sends the GET request to the web service. I'm very comfortable with PHP, but a newbie with jQuery and AJAX. I appreciate the help with this, and look forward to the day when I can help others as I've been helped here.
Here is the jQuery code:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"> </script>
<script type="text/javascript">
$(document).ready(function () {
$('#btnGetETo').click(function () {
var resultElement = $('#resultDiv');
var requestData = $('#txtZip').val();
$.ajax({
url: 'http://et.water.ca.gov/api/data?appKey=B51CF64B-C37B-406A-83F1-1DBD8CE40EEF&targets=94805&startDate=2015-07-01&endDate=2015-07-01&dataItems=day-asce-eto,day-eto,day-precip&unitOfMeasure=E;prioritizeSCS=Y',
method: 'get',
data: { q: requestData },
dataType: 'json',
success: function (response) {
if (response.message != null) {
resultElement.html(response.message);
}
else {
resultElement.html('ETo: ' + response.DayAsceEto[0].value);
}
},
error: function (err) {
alert(err);
}
});
});
});
</script>

Unfortunately, it seems that the API in question does not support JSONP. In fact, they seem to have gone out of their way to make it difficult to query via JavaScript.
Here's how to test for JSONP (not foolproof, but most mainstream JSONP-enabled services will respond correctly). Take whatever URL you were planning to send, and add &callback=foo to the end of it. (If there are no other query string parameters of course, use ? instead of &.)
If the server supports JSONP, the response should look like:
foo({
...
});
If not, it'll look like:
{
...
}
As you can see, the only difference is that JSONP-enabled servers can wrap the JSON in a function of arbitrary name. Some servers will insert a little extra code for safety/convenience. For example, the following output was generated by the JSONplaceholder API using the URL http://jsonplaceholder.typicode.com/users/1?callback=foo:
/**/ typeof foo === 'function' && foo({
"id": 1,
"name": "Leanne Graham"
...
});
The upshot of all this is that it's the API provider's fault, not yours. If I were giving them feedback I'd make the following suggestions:
Handle cross-origin requests correctly.
Allow fallback to JSONP.

Related

How to get JSON Object from URL

I'm very new to web development.
When I input this link
https://api.locu.com/v1_0/venue/search/?name=jimmy%20johns&api_key=b1f51f4ae241770f72fca5924d045733c4135412
into my browser, I can see the JSON object.
What do I need to do so can I use this JSON object in my javascript? I've tried using JQuery's $.getJSON with no luck.
EDIT
Using JSONP worked! Appending &jsonp=readJSON&?callback=? to the URL gave me back the JSON I wanted. Thank you for all the informative answers.
$.getJSON( "https://api.locu.com/v1_0/venue/search/?name=jimmy%20johns&api_key=b1f51f4ae241770f72fca5924d045733c4135412&jsonp=readJSON&?callback=?", function() {
console.log( "success" );
})
function readJSON(response){
console.log (response);
}
The question is, is this domain (api.locu.com) the same from where you serve your files? I suppose it isn't. In this case, you have two options:
Your backend can proxy the request from this site
You have to use a JSONP object if it's supported by the API
I'm no clear about your question, but I think you can use a call ajax, something like:
$.ajax({
url: "https://api.locu.com/v1_0/venue/search/?name=jimmy%20johns&api_key=b1f51f4ae241770f72fca5924d045733c4135412",
type: 'get',
cache: false,
success: function (response) {
console.log(response);
}
});
This should get the concept across if you are using JQuery... but you can use just about anything.
var url = "https://api.locu.com/v1_0/venue/search/?name=jimmy%20johns&api_key=b1f51f4ae241770f72fca5924d045733c4135412";
var result;
var settings = {
success: function(data){
result = data;
//do anything else related to this data here as you need it fetched, and is not linear.
}
}
$.ajax(url, settings);
Now, I noticed you used getJSON, which is pretty much the exact same. I did not however see you use a success function, so if you did your way, have you tried:
$.getJSON(url, function(data){
result = data;
});
I may be mistaken, but you say: "With no luck" so i have a limited understanding as to what you tried with $.getJSON
Not directly from inside a web browser, no. You would need to use a proxy: another server that makes this request in your behalf and then gives you the result.
Why not?
Web browsers are pretty tight on security. One of the strategies for protecting users from malicious activity is restricting the domains your Javascript can make HTTP requests to.
An HTTP request from your domain (the origin) to another domain is called a cross-origin request. These are forbidden by default, and you won't be able to read the response body, unless the received HTTP response includes the header Access-Control-Allow-Origin.
How then?
By using a proxy as an intermediary. The proxy is not a web browser, it doesn't care about Access-Control-Allow-Origin, and will read the response anyway.
There are a number of proxies you can use. An easy one is YQL (the Yahoo Query Language). Here's an article on the topic, using jQuery: http://ajaxian.com/archives/using-yql-as-a-proxy-for-cross-domain-ajax

How to print content that is returned in http response using javascript

I want to print in console content that are returned in http response. For example when I go to https://google.com and in the tab Network I can see content such as scripts, text, document, png. I want to print names of all .png files.
I tried to use something like that:
function hand () {
console.log(this.getResponseHeader('content-type'));
}
var x = new XMLHttpRequest();
x.open('GET', 'https://google.com', true);
x.onreadystatechange = hand;
x.send();
But it doesn't work for me. This action below is assigned for the button on me page.
Cross-origin requests simply are not allowed by default. The remote server may provide permission to your application through CORS or by supporting Ajax alternatives like JSONP.
Edited:
The only (easy) way to get cross-domain data using AJAX is to use a server side language as the proxy as Andy E noted. Here's a small sample how to implement that using jQuery:
The jQuery part:
$.ajax({
url: 'proxy.php',
type: 'POST',
data: {
address: 'http://www.google.com'
},
success: function(response) {
// response now contains full HTML of google.com
}
});
Simple as that. Just be aware of what you can or cannot do with the scraped data and be very much aware that such a proxy is a severe security hole. At least make a list of acceptable addresses and don't just blindly accept any passed address. Have a look at a decent proxy script here: PHP Simple Proxy

Adding a contact using Google Contact API in javascript

I am playing with Google API in javascript. I managed to get a list of my contact with the following code :
$.ajax({
url: 'https://www.google.com/m8/feeds/contacts/default/full?access_token=' + access_token + '&alt=json',
method: 'GET',
error: function(error) {
alert('An error has occured during contact creation.');
},
success: function(data, status){
console.log(data);
}
});
I tried to add a contact by changing GET to POST and adding my contact data in the request body. But as soon as I add a data attribute, or change GET to POST, the server answers me the really annoying "No 'Access-Control-Allow-Origin" error.
Any idea?
I am following this documentation : https://developers.google.com/google-apps/contacts/v3/?csw=1#creating_contacts
Thanks a lot
It is possible to do this from the browser, although not obvious at all.
Based on this SO answer, we learn that there is method called gapi.client.request that can be used for this (instead of jQuery's $.ajax).
Accordingly, for editing we can do:
gapi.client.request({
method : 'PUT',
path:'m8/feeds/contacts/default/full/<contactId>/<editRevisionFromGET>',
body : {"version":"1.0","encoding":"UTF-8","entry": ...},
callback : function(data) {
console.log(data);
}
});
The important parts for editing in here are:
send back the entire entry you got before from a read
use the current ID given at the end of the URL in the entry.link element with relation type edit (or you'll get a HTTP Status 409 - Conflict)
Side note:
Notice that these requests actually are done to https://content.googleapis.com/ ...
From some quick tests, it seems you can do ?all? requests just to that URL instead of google.com, and then CORS issues disappear.

Error in making cross domain request using jquery for json content

I am trying to call a service which returns the data in json format. I am using jquery-ajax request to get that response data.
$('#butCallAjax').click(function () {
$.ajax({
url: 'my service url',
type: 'GET',
data: {},
success: function (data) {
if (data == "success") {
alert('request sent!');
}
},
error: function () {
alert('error');
}
});
});
using this code I am getting error
Origin 'servername' is not allowed by Access-Control-Allow-Origin.
Then I found some answers here and solved that by using dataType:'jsonp' in the request But when I use this dataType:'jsonp' then I am getting this error
Uncaught Syntax Error: Unexpected token :
I understand that this is because of Service is returning 'json' instead of jsonp.
So I am not able to figured it out that how to call a service that returns the json content and taking care of cross domain request.
Js Fiddle Try
That doesnt answer your question directly but its also a way to achieve what you're trying:
You can use:
/* java side: */
$.getJSON("URL?some_call_back_function=?", dataToPass, function(data){
// do whatever you like..
});
/* php side: */
if(isset($_GET['some_call_back_function']) && $_GET['some_call_back_function'] != ''){
$someJsonToReturn = array('Something'=> "something");
echo $_GET['some_call_back_function'].'('.json_encode($someJsonToReturn ).')';
}
i hope that helps. i use that usually when i want cross domain.
here is the jquery API for it:
getJson API
You are trying to make a cross domain call which fails.
I have modified your jsFiddle and added
async: false,
cache:false
Plus added errorObject parameter to the "Error" in ajax.
you can see my changes here
The answer I got now was "network error dom exception 19".
DOM Exception 19 refers to a "Network Error".
Is the URL that you are contacting in your Ajax call available?
Cross domain requests are possible if the server supports it! Before making the actual GET/POST call, the browser issues an OPTIONS call to the server to check whether it supports cross domain requests. Check if the server that you are contacting supports cross domain requests.
For more details on cross domain requests refer to this article which is very helpful:
using CORS

Getting 'data is null' on a Twitter API call but displays data in browser

I'm trying to display the follow count of a twitter account, but when I hook into the API using this code:
$.getJSON("https://api.twitter.com/1/users/show.json?screen_name=uswitchTech&include_entities=true", function(data) {
console.log(data);
if (!data.error) {
$("#followers").html(data.followers_count);
}
});
I get a 200 ok report but with Data is null message.
But if I download the json file to my local machine and change the getJSON call accordingly, it works straight away.
Has anyone got any ideas on what could be causing this?
Thanks
Also just to add, if I put the Twitter API url into my browser it displays all the data, which makes it even weirder.
Maybe the problem lies with jsonP, since you are calling a remote server and you must specify you should use jsonP. Have you tried adding callback=? as a parameter
$.getJSON("https://api.twitter.com/1/users/show.json?screen_name=uswitchTech&include_entities=true&callback=?", function(data) {
if (!data.error) {
$("#followers").html(data.followers_count);
}
});
Taken from jQuery docs
JSONP
If the URL includes the string "callback=?" (or similar, as
defined by the server-side API), the request is treated as JSONP
instead. See the discussion of the jsonp data type in $.ajax() for
more details.
$.ajax({
url: 'https://api.twitter.com/1/users/show.json?screen_name=uswitchTech&include_entities=true',
dataType: 'jsonp',
success: function(data){
console.log(data.followers_count);
}
});

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