Cross-domain AJAX calls

In these days all web2.0 apps make use of AJAX to save bandwidth, user time or to display data without refreshing the page. When you make an AJAX request the response could be plain text, Html or JSON, but if you want to make a cross-domain AJAX call you can’t because the browser security model dictates that XMLHttpRequest must have the same domain in order to communicate. This is where you need to use JSONP, this technique will make the AJAX call and after will inject the response in a script tag and will pass the data to a specified function.

Some JavaScript Libraries help you dealing with JSONP and in this article I will show you how to make cross-domain AJAX calls with MooTools and jQuery.

MooTools

If you want to make JSONP requests you need the plugin Request.JSONP from MooTools More.

var myRequest = new Request.JSONP({
	url: 'http://twitter.com/statuses/user_timeline/twitter.json',
	onComplete: function(data) {
		//do something with data
	}
}).send();

MooTools will automatically add callback parameter with function which will handle the response, but if the server requires another parameter for callback you can add the callBackKey option. If you need to pass data to request you need to add the values in data option.

var myRequest = new Request.JSONP({
	url: 'http://domain.com/getData',
	callBackKey: 'callback',
	data: {
		someData: 'someValue'
	},
	onComplete: function(data) {
		//do something with data
	}
}).send();

jQuery

If you worked before with $.ajax there are no big difference between a request for HTML/JSON and JSONP calls, you need just to change dataType to jsonp and to specify the callback parameter in jsonp option.

$.ajax({
	url: 'http://twitter.com/statuses/user_timeline/twitter.json&callback=?',
	dataType: 'jsonp',
	jsonp: 'callback',
	success: function(data){
		//do something with data
	}
});

You can read more about JSONP here.

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