Design Patterns

CHAPTER 14 ■ THE PROXY PATTERN 203
First, define the interface for the web service. This allows you to swap out different types
of proxies later on, if need be:
/* PageStats interface. */
var PageStats = new Interface('PageStats', ['getPageviews', 'getUniques',
'getBrowserShare', 'getTopSearchTerms', 'getMostVisitedPages']);
Then define the remote proxy itself, StatsProxy:
/* StatsProxy singleton. */
var StatsProxy = function() { // implements PageStats
/* Private attributes. */
var xhrHandler = XhrManager.createXhrHandler();
var urls = {
pageviews: '/stats/getPageviews/',
uniques: '/stats/getUniques/',
browserShare: '/stats/getBrowserShare/',
topSearchTerms: '/stats/getTopSearchTerms/',
mostVisitedPages: '/stats/getMostVisitedPages/'
};
/* Private methods. */
function xhrFailure() {
throw new Error('StatsProxy: Asynchronous request for stats failed.');
}
function fetchData(url, dataCallback, startDate, endDate, page) {
var callback = {
success: function(responseText) {
var stats = eval('(' + responseText + ')');
dataCallback(stats);
},
failure: xhrFailure
};
var getVars = [];
if(startDate != undefined) {
getVars.push('startDate=' + encodeURI(startDate));
}
if(endDate != undefined) {
getVars.push('endDate=' + encodeURI(endDate));
}