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JavaScript & AJAX

Quick Tip: Cross Domain AJAX Request with YQL and jQuery

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For security reasons, we cannot make cross-domain AJAX requests with jQuery. For example, I can't call the load() method, and pass in 'cnn.com'. As we'd be loading in scripts and such, as well as our desired content, this would present a significant security risk. Nonetheless, there may be times when this is specifically what you require. Thanks to YQL, we can allow for this functionality rather easily!

The Script

// Accepts a url and a callback function to run.
function requestCrossDomain( site, callback ) {
	
	// If no url was passed, exit.
	if ( !site ) {
		alert('No site was passed.');
		return false;
	}
	
	// Take the provided url, and add it to a YQL query. Make sure you encode it!
	var yql = 'http://query.yahooapis.com/v1/public/yql?q=' + encodeURIComponent('select * from html where url="' + site + '"') + '&format=xml&callback=cbFunc';
	
	// Request that YSQL string, and run a callback function.
	// Pass a defined function to prevent cache-busting.
	$.getJSON( yql, cbFunc );
	
	function cbFunc(data) {
	// If we have something to work with...
	if ( data.results[0] ) {
		// Strip out all script tags, for security reasons.
		// BE VERY CAREFUL. This helps, but we should do more. 
		data = data.results[0].replace(/<script[^>]*>[\s\S]*?<\/script>/gi, '');
		
		// If the user passed a callback, and it
		// is a function, call it, and send through the data var.
		if ( typeof callback === 'function') {
			callback(data);
		}
	}
	// Else, Maybe we requested a site that doesn't exist, and nothing returned.
	else throw new Error('Nothing returned from getJSON.');
	}
}

Call the Function

requestCrossDomain('http://www.cnn.com', function(results) {
   $('#container').html(results);
});

Stripping Out the Script Tags

I had to progress rather quickly in the video, so perhaps the regular expression that strips out the <script> tags require further detail.

.replace(/<script[^>]*>[\s\S]*?<\/script>/gi, '');

When we load our desired page, it's also going to load scripts! You must be very careful when making cross domain request. It definitely helps to strip out the <script> tags, but you should do more in an actual project.

Let's take the regular expression step by step.

<script[^>]*>

Find all open script tags; however, they could come in many forms: <script type="text/javascript" src="bla.js"></script> , or <script type="text/javascript">lots of code here...</script> . For this reason, we add a character class ( [^>]* ), which mean, "Find zero or more of anything that IS NOT a closing bracket. This will take care of the attributes and values.

[\s\S]*?

Next, we want to strip out all code, as well as any spacing. \s refers to a space. \S refers to anything that IS NOT a space. Once again, we add a * after the character class to designate that we want zero or more occurrences.

<\/script>

Finally, find the closing script tags.


Further Reading

This is only meant to provide a glimpse of how we can achieve this functionality. Only so much can be covered in a five minute video. Feel free to discuss in the comments, and you're always encouraged to fork the source code to improve upon it!

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