How to get data with JavaScript from another serve

Question

How can I make requests to other server(s) (i.e. get a page from any desired server) with a JavaScript within the user's browser? There are limitations in place to prevent this for methods like XMLHttpRequest, are there ways to bypass them or other methods?

That is a general question, specifically I want to check a series of random websites and see if they contain a certain element, so I need the HTML content of a website without downloading any additional files; all that in a JavaScript file, without any forwarding or proxy mechanism on a server.

(Note: one way is using Greasemonkey and its GM_xmlhttpRequest.)

Answer 1

You can also use a iframe to emulate an ajax request. This saves you the mess of having to code a Backend solution for a Frontend problem. Here is an example:

function setUploadEvent(typeComponet){
       var eventType = "";
       var iframe = document.getElementById("iframeId");
       try{
           /* for Mozilla / Opera9 */
           if (/(?!.*?compatible|.*?webkit)^mozilla|opera/i.test(navigator.userAgent)) {
                eventType = "onload";
           }else{
           /* IE  */
                eventType = "onreadystatechange";
           }

           iframe[eventType] = function(){
                var doc = iframe.contentDocument || iframe.contentWindow.document;
                var response = doc.body.innerHTML; /* or what ever content you are looking for */
             }
           }
       catch(e){
           alert("Error loading content")}
       } 

That should do the trick. Please note that the Browser detection line is not the cleanest, you should absolutely use the ones provided in all the most common JS frameworks (Prototype, JQuery, etc)

Answer 2

update 2018:

You can only access cross domain with the following 4 condition

• in response header has Access-Control-Allow-Origin: *

Demo

$.ajax({
  url: 'https://api.myjson.com/bins/bq6eu',
  success: function(response){
    console.log(response.string);
  },
  error: function(response){
    console.log('server error');
  }
})

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

• use server as bridge or proxy to the target

Demo:

$.ajax({
  url: 'https://cors-anywhere.herokuapp.com/http://whatismyip.akamai.com/',
  success: function(response){
    console.log('server IP: ' + response);
  },
  error: function(response){
    console.log('bridge server error');
  }
})

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

• using browser addon to enable Allow-Control-Allow-Origin: *
• disable browser web security

Chrome

chrome.exe --args --disable-web-security

Firefox

about:config -> security.fileuri.strict_origin_policy -> false

end

---

noob old answer 2011

$.get(); can get data from jsbin.com but i don't know why it can't get data from another site like google.com

$.get('http://jsbin.com/ufotu5', {},
  function(results){  alert(results); 
});

demo: http://jsfiddle.net/Xj234/ tested with firefox, chrome and safari.