A Caching XmlHttpRequest Wrapper
/* XmlHttpRequest Wrapper Version 1.2.2 29 Jul 2005 adamv.com/dev/ */ var Http = { ReadyState: { Uninitialized: 0, Loading: 1, Loaded:2, Interactive:3, Complete: 4 }, Status: { OK: 200, Created: 201, Accepted: 202, NoContent: 204, BadRequest: 400, Forbidden: 403, NotFound: 404, Gone: 410, ServerError: 500 }, Cache: { Get: 1, GetCache: 2, GetNoCache: 3, FromCache: 4 }, Method: {Get: "GET", Post: "POST", Put: "PUT", Delete: "DELETE"}, enabled: false, logging: false, _get: null, // Reference to the XmlHttpRequest object _cache: new Object(), Init: function(){ Http._get = Http._getXmlHttp() Http.enabled = (Http._get != null) Http.logging = (window.Logging != null); }, _getXmlHttp: function(){ /*@cc_on @*//*@if (@_jscript_version >= 5) try { return new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) {} try { return new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) {} @end @*/ try { return new XMLHttpRequest();} catch (e) {} return null; }, /* Params: url: The URL to request. Required. cache: Cache control. Defaults to Cache.Get. callback: onreadystatechange function, called when request is completed. Optional. method: HTTP method. Defaults to Method.Get. */ get: function(params, callback_args){ if (!Http.enabled) throw "Http: XmlHttpRequest not available."; var url = params.url; if (!url) throw "Http: A URL must be specified"; var cache = params.cache || Http.Cache.Get; var method = params.method || Http.Method.Get; var callback = params.callback; if ((cache == Http.Cache.FromCache) || (cache == Http.Cache.GetCache)) { var in_cache = Http.from_cache(url, callback, callback_args) if (Http.logging){ Logging.log(["Http: URL in cache: " + in_cache]); } if (in_cache || (cache == Http.Cache.FromCache)) return in_cache; } if (cache == Http.Cache.GetNoCache) { var sep = (-1 < url.indexOf("?")) ? "&" : "?" url = url + sep + "__=" + encodeURIComponent((new Date()).getTime()); } // Only one request at a time, please if ((Http._get.readyState != Http.ReadyState.Uninitialized) && (Http._get.readyState != Http.ReadyState.Complete)){ this._get.abort(); if (Http.logging){ Logging.log(["Http: Aborted request in progress."]); } } Http._get.open(method, url, true); Http._get.onreadystatechange = function() { if (Http._get.readyState != Http.ReadyState.Complete) return; if (Http.logging){ Logging.log(["Http: Returned, status: " + Http._get.status]); } if ((cache == Http.Cache.GetCache) && (Http._get.status == Http.Status.OK)){ Http._cache[url] = Http._get.responseText; } if (callback_args == null) callback_args = new Array(); var cb_params = new Array(); cb_params.push(Http._get); for(var i=0;i<callback_args.length;i++) cb_params.push(callback_args[i]); callback.apply(null, cb_params); } if(Http.logging){ Logging.log(["Http: Started\n\tURL: " + url + "\n\tMethod: " + method + "; Cache: " + Hash.keyName(Http.Cache,cache)]) } Http._get.send(params.body || null); }, from_cache: function(url, callback, callback_args){ var result = Http._cache[url]; if (result != null) { var response = new Http.CachedResponse(result) var cb_params = new Array(); cb_params.push(response); for(var i=0;i<callback_args.length;i++) cb_params.push(callback_args[i]); callback.apply(null, cb_params); return true } else return false }, clear_cache: function(){ Http._cache = new Object(); }, is_cached: function(url){ return Http._cache[url]!=null; }, CachedResponse: function(response) { this.readyState = Http.ReadyState.Complete this.status = Http.Status.OK this.responseText = response } } Http.Init() function json_response(response){ var js = response.responseText; try{ return eval(js); } catch(e){ if (Http.logging){ Logging.logError(["json_response: " + e]); } else{ alert("Error: " + e + "\n" + js); } return null; } } function getResponseProps(response, header){ try { var s = response.getResponseHeader(header || 'X-Ajax-Props'); if (s==null || s=="") return new Object() else return eval("o="+s) } catch (e) { return new Object() } }
Caching Options
These options only make sense to use with the GET method. POST operations should not be cached.
Http.Cache.Get
Perform a normal request, and do not add the result to the local cache. Note: on IE, requesting the same URL via GET multiple times will cause IE to cache the result internally.
Http.Cache.GetCache
Perform a request and cache the result if sucessful. If the requested URL's response is already cached locally, do not perform the server request.
Http.Cache.GetNoCache
Perform a request and add a time-based variable to the querystring to force IE not to cache the result. The result is not placed in the local cache.
Http.Cache.FromCache
If the requested URL's response has already been cached, call the supplied callback on the locally cached version. Http.get will return true or false based on whether or not the response is in the cache.