AJAX Call

ajaxCall.js

var cache = {};

function getData( val ){

	// Return a promise from the cache (if available)
	// or create a new one (a jqXHR object) and store it in the cache.
	var promise = cache[val];
	if (!promise) {
		promise = $.ajax('/foo/', {
			data: { value: val },
			dataType: 'json'
		});
		cache[val] = promise;
	}
	return promise;
}

$.when(getData('foo')).then(function(resp){
	// do something with the response, which may
	// or may not have been retrieved using an
	// XHR request.
});