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1、word文档整理分享UsingtheXMLHttpRequestObjectNowthatwe’vediscussedthehistoryofdynamicWebapplicationsandintroducedAjax,it’stimetocovertheheartofthematter:howtousetheXMLHttpRequestobject.WhileAjaxismoreofatechniquethanatechnology,withoutwidespreadsupportforXMLH
2、ttpRequest,GoogleSuggestandTa-daListwouldn’texistaswecurrentlyknowthem.Andyouwouldn’tbereadingthisbook!XMLHttpRequestwasoriginallyimplementedinInternetExplorer5asanActiveXcomponent.ThatitworkedonlyinInternetExplorerkeptmostdevelopersfromusingXMLHttpReq
3、uestuntilitsrecentadoptionasadefactostandardinMozilla1.0andSafari1.2.It’simportanttonotethatXMLHttpRequestisnotaW3Cstandard,thoughmuchofthefunctionalityiscoveredinanewproposal:theDOMLevel3LoadandSaveSpecification.Becauseitisnotastandard,itsbehaviormayd
4、ifferslightlyfrombrowsertobrowser,thoughmostmethodsandpropertiesarewidelysupported.Currently,Firefox,Safari,Opera,Konqueror,andInternetExplorerallimplementthebehavioroftheXMLHttpRequestobjectsimilarly.Thatsaid,ifasignificantnumberofyourusersstillaccess
5、yoursiteorapplicationwitholderbrowsers,youwillneedtoconsideryouroptions.AswediscussedinChapter1,ifyouaregoingtouseAjaxtechniques,youneedtoeitherdevelopanalternativesiteorallowyourapplicationtodegradegracefully.Withmostusagestatisticsindicatingthatonlya
6、smallfractionofbrowsersinusetodaylackXMLHttpRequestsupport,thechancesofthisbeingaproblemareslim.However,youneedtocheckyourWeblogsanddeterminewhatclientsyourcustomersareusingtoaccessyoursites.OverviewoftheXMLHttpRequestObjectYoumustfirstcreateanXMLHttpR
7、equestobjectusingJavaScriptbeforeyoucanusetheobjecttosendrequestsandprocessresponses.SinceXMLHttpRequestisnotaW3Cstandard,youcanuseJavaScriptin参考资料word文档整理分享acoupleofwaystocreateaninstanceofXMLHttpRequest.InternetExplorerimplementsXMLHttpRequestasanAct
8、iveXobject,andotherbrowserssuchasFirefox,Safari,andOperaimplementitasanativeJavaScriptobject.Becauseofthesedifferences,theJavaScriptcodemustcontainlogictocreateaninstanceofXMLHttpRequestusingtheActiveXtechniqueorusingthenativeJavaScript
