外文翻译 - JavaScript的权威指南

0外文原文JavaScriptTheDefinitiveGuideJavaScriptistheprogramminglanguageoftheWeb.TheoverwhelmingmajorityofmodernwebsitesuseJavaScript,andallmodernwebbrowsersondesktops,gameconsoles,tablets,andsmartphonesincludeJavaScriptinterpreters,makingJavaScriptthemostubiquitousprogramminglanguageinhistory.JavaScriptispartofthetriadoftechnologiesthatallWebdevelopersmustlearn:HTMLtospecifythecontentofwebpages,CSStospecifythepresentationofwebpages,andJavaScripttospecifythebehaviorofwebpages.Ifyouarealreadyfamiliarwithotherprogramminglanguages,itmayhelpyoutoknowthatJavaScriptisahigh-level,dynamic,untypedinterpretedprogramminglanguagethatiswell-suitedtoobject-orientedandfunctionalprogrammingstyles.JavaScriptderivesitssyntaxfromJava,itsfirst-classfunctionsfromScheme,anditsprototype-basedinheritancefromSelf.Butyoudonotneedtoknowanyofthoselanguages,orbefamiliarwiththoseterms,tousethisbookandlearnJavaScript.ThenameJavaScriptisactuallysomewhatmisleading.Exceptforasuperficialsyntacticresemblance,JavaScriptiscompletelydifferentfromtheJavaprogramminglanguage.AndJavaScripthaslongsinceoutgrownitsscripting-languagerootstobecomearobustandefficientgeneral-purposelanguage.Thelatestversionofthelanguage(seethesidebar)definesnewfeaturesforseriouslarge-scalesoftwaredevelopment.LexicalStructureThelexicalstructureofaprogramminglanguageisthesetofelementaryrulesthatspecifieshowyouwriteprograminthatlanguage.Itisthelowest-levelsyntaxofalanguage;itspecifiessuchthingsaswhatvariablenameslooklike,thedelimitercharactersforcomments,andhowoneprogramstatementisseparatedfromthenext.ThisshortchapterdocumentsthelexicalstructureofJavaScript.Types，Values，andVariables1Computerprogramsworkbymanipulatingvalues,suchasthenumber3.14orthetext“HelloWorld.”Thekindsofvaluesthatcanberepresentedandmanipulatedinaprogramminglanguageareknownastypes,andoneofthemostfundamentalcharacteristicsofaprogramminglanguageisthesetoftypesitsupports.Whenaprogramneedstoretainavalueforfutureuse,itassignsthevalueandallowsthevaluetobereferredtobyname.Thewaythatvariablesworkisanotherfundamentalcharacteristicofanyprogramminglanguage.Thischapterexplainstypes,values,andvariablesinJavaScript.JavaScripttypescanbedividedintotwocategories:primitivetypesandobjecttypes.JavaScriptsprimitivetypeincludenumbers,stringoftext(knownasstring),andBooleantruthvalues(knownasBoolean).AsignificantportionofthischapterisdedicatedtoadetailedexplanationofthenumericandstringtypesinJavaScript.ThespecialJavaScriptvaluesnullandundefinedareprimitivevalues,buttheyarenotnumbers,strings,orBooleans.Eachvaluesistypicallyconsideredtobethesolememberofitsownspecialtype.AnyJavaScriptvaluethatisnotanumber,astring,aBoolean,ornullorundefinedisanobject.Anobject(thatis,amemberofthetypeobject)isacollectionofpropertieswhereeachpropertyhasanameandavalue(eitheraprimitivevalue,suchasnumberorstring,oranobject).ExpressionsandOperatorsAnexpressionisaphraseofJavaScriptthataJavaScriptinterpretercanevaluatetoproduceavalue.Aconstantembeddedliterallyinyourprogramisaverysimplekindofexpression.Avariablenameisalsoasimpleexpressionthatevaluatestowhatevervaluehasbeenassignedtothatvariable.Complexexpressionsarebuiltfromsimplerexpressions.Anarrayaccessexpression,forexample,consistsofoneexpressionthatevaluatestoanarrayfollowedbyanopensquarebracket,anexpressionthatevaluatestoaninteger,andaclosesquarebracket.Thisnew,morecomplexexpressionevaluatestothevaluestoredatthespecifiedindexofthespecifiedarray.Similarly,afunctioninvocationexpressionconsistsofoneexpressionthatevaluatestofunctionobjectandzeroormoreadditionalexpressionsthatareusedastheargumentstofunction.PrimaryExpressionsThesimplestexpressions,knownasprimaryexpressions,arethosethatstandalone2theydonotincludeanysimplerexpressions.PrimaryexpressionsinJavaScriptareconstantorliteralvalues,certainlanguagekeywords,andvariablereferences.Literalsareconstantvaluesthatareembeddeddirectlyinyourprogram.SomeofJavaScriptsreservedwordsareprimaryexpression:true,false,null,thisWelearnedabouttrue,false,andnull.Unliketheotherkeywords,thisisnotaconstantitevaluatestodifferentvaluesindifferentplacesintheprogram.Thethiskeywordisusedinobject-orientedprogramming.Withinthebodyofamethod,thisevaluatestotheobjectonwhichthemethodwasinvoked.Whenanyidentifierappearsbyitselfinaprogram,JavaScriptassumesitisavariableandlooksupitsvalue.Ifnovariablewiththatnameexists,theexceptionevaluatestotheundefinedvalue.InthestrictmodeifECMAScript5,however,anattempttoevaluateanonexistentvariablethrowsaReferenceErrorinstead.TheJavaprogramminglanguageandplatformhaveemergedasmajortechnologiesforperforminge-businessfunctions.Javaprogrammingstandardshaveenableedportabilityofapplicationsandthereuseofapplicationcomponentsacrosscomputingplatforms.SunMicrosystemsJavaCommunityProcesscontinuestobeastrongbaseforthegrowthoftheJavainfrastructur-eandlanguagestandards.Thisgrowthofopenstandardscreatesnewopportunitiesfordesignersanddevelopersofapplicationsandservices.ApplicationsofJavaJavausesmanyfamiliarprogrammingconceptsandconstructsandallowsportabilitybyprovidingacommoninterfacethroughanexternalJavaVirtualMachine(JVM).Avirtualmachineisaself-containedoperatingenvironment,createdbyasoftwarelayerthatbehavesasifitwereaseparatecomputer.Benefitsofcreatingvirtualmachinesincludebetterexploitationofpowerfulcomputingresourcesandisolationofapplicationstopreventcross-corruptionandimprovesecurity.TheJVMallowscomputingdeviceswithlimitedprocessorsormemorytohandlemoreadvancedapplicationsbycallingupsoftwareinstructionsinsidetheJVMtoperformmostofthework.ThisalsoreducesthesizeandcomplexityofJavaapplicationsbecausemanyofth3ecorefunctionsandprocessinginstructionswerebuiltintotheJVM.Asaresult,softwaresameapplicationforeveryoperatingsystem.Javaalsoprovidessecuritybyinstructingtheapplicationtointeractwiththevirtualmachine,whichservedasabarrierbetweenapplicationsandthecoresystem,effectivelyprotectingsystemsfrommaliciouscode.Amongotherthings,Javaistailor-madeforthegrowingInternetbecauseitmakesiteasytodevelopnew,dynamicapplicationsthatcouldmakethemostoftheInternetspowerandcapabilities.Javaisnowanopenstandard,meaningthatnosingleentitycontrolsitsdevelopmentandthetoolsforwritingprogramsinthelanguageareavailabletoeveryone.ThepowerofopenstandardslikeJavaistheabilitytobreakdownbarriersandspeedupprogress.Today,youcanfindJavatechnologyinnetworksanddevicesthatrangefromtheInternetandscientificsupercomputerstolaptopsandcellphones,fromWallStreetmarketsimulatorstohomegameplayersandcreditcards.Thereareover3millionJavadevelopersandnowthereareseveralversionsofthecode.Mostlargecorporationshavein-houseJavadevelopers.Inaddition,themajorityofkeysoftwarevendorsuseJavaintheircommercialapplications(Lazaridis,2003).ApplicationsJavaontheWorldWideWebJavahasfoundaplaceonsomeofthemostpopularwebsitesintheworldandtheusesofJavacontinuestogrow.Javaapplicationsnotonlyprovideuniqueuserinterfaces,theyalsohelptopowerthebackendofwebsites.EverybodyisprobablyfamiliarwitheBayandAmazonhavebeenJavapioneersontheWorldWideWeb.eBayFoundedin1995,eBayenablese-commerceonalocal,nationalandinternationalbasiswithanarrayofWebsites.YoucanfinditoneBay,evenifyoudidntknowitexisted.Onatypicalday,morethan100millionitemsarelistedoneBayintensofthousandsofcategories.oneBay;theworldslargestonlinemarketplace.eBayusesJavaalmosteverywhere.Toaddresssomesecurityissues,eBaychoseSunMicrosystemsJavaSystemIdentityManagerastheplatformforrevampingitsidentitymanag4ementsystem.Thetaskathandwastoprovideidentitymanagementformorethan12,000eBayemployeesandcontractors.NowmorethanathousandeBaysoftwaredevelopersworkdailywithJavaapplications.JavasinherentportabilityallowseBaytomovetonewhardwaretotakeadvantageofnewtechnology,packaging,orpricing,withouthavingtorewriteJavacode.AmazonAhascreatedaWebServiceapplicationthatenablesuserstobrowsetheirproductcatalogandplaceorders.AusesaJavaapplicationthatsearchestheAmazoncatalogforbookswhosesubjectmatchesauser-selectedtopic.Theapplicationdisplaystenbooksthatmatchthechosentopic,andshowstheauthorname,booktitle,listprice,Amazondiscountprice,andthecovericon.Theusermayoptionallyviewonereviewperdisplayedtitleandmakeabuyingdecision.JavainDataWarehousing&MiningAlthoughmanycompaniescurrentlybenefitfromdatawarehousingtosupportcorporatedecisionmaking,newbusinessintelligenceapproachescontinuetoemergethatcanbepoweredbyJavatechnology.Applicationssuchasdatawarehousing,datamining,EnterpriseInformationPortalsandKnowledgeManagementSystemsareabletoprovideinsightintocustomerretention,purchasingpatterns,andevenfuturebuyingbehavior.Theseapplicationscannotonlytellwhathashappenedbutwhyandwhatmayhappengivencertainbusinessconditions;Asaresultofthisinformationgrowth,peopleatalllevelsinsidetheenterprise,aswellassuppliers,customers,andothersinthevaluechain,areclamoringforsubsetsofthevaststoresofinformationtohelpthemmakebusinessdecisions.Whilecollectingandstoringvastamountsofdataisonething,utilizinganddeployingthatdatathroughouttheorganizationisanother.Thetechnicalchallengesinherentinintegratingdisparatedataformats,platforms,andapplicationsaresignificant.However,emergingstandardssuchastheApplicationProgrammingInterfacesthatcomprisetheJavaplatform,aswellasExtendableMarkupLanguagetechnologiescanfacilitatetheinterchangeofdataandthedevelopmentofnextgenerationdatawarehousingandbusinessintelligenceapplications.WhileJavatechnologyhasbeenusedextensivelyforclientsideaccessandtopresentationlayerchallenges,itisrapidlyemergingasasignificanttoolfordevelopingscaleableserversideprograms.TheJava2Platform,Enter5priseEdition(J2EE)providestheobject,transaction,andsecuritysupportforbuildingsuchsystems.MetadataIssuesOneofthekeyissuesthatbusinessintelligencedevelopersmustsolveisthatofincompatiblemetadataformats.Metadatacanbedefinedasinformationaboutdataorsimplydataaboutdata.Inpractice,metadataiswhatmosttools,databases,applications,andotherinformationprocessesusetodefine,relate,andmanipulatedataobjectswithintheirownenvironments.Itdefinesthestructureandmeaningofdataobjectsmanagedbyanapplicationsothattheapplicationknowshowtoprocessrequestsorjobsinvolvingthosedataobjects.Developerscanusethisschematocreateviewsforusers.Also,userscanbrowsetheschematobetterunderstandthestructureandfunctionofthedatabasetablesbeforelaunchingaquery.Toaddressthemetadataissue,agroupofcompanieshavejoinedtodeveloptheJavaMetadataInterface(JMI)API.TheJMIAPIpermitstheaccessandmanipulationofmetadatainJavawithstandardmetadataservices.JMIisbasedontheMetaObjectFacility(MOF)specificationfromtheObjectManagementGroup(OMG).TheMOFprovidesamodelandasetofinterfacesforthecreation,storage,access,MetamodelandmetadatainterchangeisdoneviaXMLandusestheXMLMetadataInterchange(XMI)specification,alsofromtheOMG.JMIleveragesJavatechnologytocreateanend-to-enddatawarehousingandbusinessintelligencesolutionsframework.EnterpriseJavaBeansAkeytoolprovidedbyJ2EEisEnterpriseJavaBeans(EJB),anarchitectureforthedevelopmentofcomponent-baseddistributedbusinessapplications.ApplicationswrittenusingtheEJBarchitecturearescalable,transactional,secure,andmulti-useraware.TheseapplicationsmaybewrittenonceandthendeployedonanyserverplatformthatsupportsJ2EE.TheEJBarchitecturemakesiteasyfordeveloperstowritecomponents,sincetheydonotneedtounderstandordealwithcomplex,system-leveldetailssuchasthreadmanagement,resourcepooling,andtransactionandsecuritymanagement.Thisallowsforrole-6baseddevelopmentwherecomponentassemblers,platformprovidersandapplicationassemblerscanfocusontheirareaofresponsibilityfurthersimplifyingapplicationdevelopment.DataStorage&AccessDatastoredinexistingapplicationscanbeaccessedwithspecializedconnectors.Integrationandinteroperabilityofthesedatasourcesisfurtherenabledbythemetadatarepositorythatcontainsmetamodelsofthedatacontainedinthesources,whichthencanbeaccessedandinterchangeduniformlyviatheJMIAPI.Thesemetamodelscapturetheessentialstructureandsemanticsofbusinesscomponents,allowingthemtobeaccessedandqueriedviatheJMIAPIortobeinterchangedviaXML.Throughalloftheseprocesses,theJ2EEinfrastructureensuresthesecurityandintegrityofthedatathroughtransactionmanagementandpropagationandtheunderlyingsecurityarchitecture.Toconsolidatehistoricalinformationforanalysisofsalesandmarketingtrends,adatawarehouseisoftenthebestsolution.Inthisexample,datacanbeextractedfromtheoperationalsystemswithavarietyofExtract,TransformandLoadtools(ETL).ThemetamodelsallowEJBsdesignedforfiltering,transformation,andconsolidationofdatatooperateuniformlyondatafromdiversedatasourcesasthebeanisabletoquerythemetamodeltoidentifyandextractthepertinentfields.Queriesandreportscanberunagainstthedatawarehousethatcontainsinformationfromnumeroussourcesinaconsistent,enterprise-widefashionthroughtheuseoftheJMIAPI.JavainIndustrialSettingsManypeopleknowJavaonlyasatoolontheWorldWideWebthatenablessitestoperformsomeoftheirfancierfunctionssuchasinteractivityandanimation.However,theactualusesforJavaaremuchmorewidespread.SinceJavaisanobject-orientedlanguage,thetimeneededforapplicationdevelopmentisminimal.Inaddition,Javasautomaticmemorymanagementandlackofpointersremovesomeleadingcausesofprogrammingerrors.Mostimportantly,applicationdevelopersdonotneedtocreatedifferentversionsofthesoftwarefordifferentplatforms.TheadvantagesavailablethroughJavahaveevenfoundtheirwayintohardware.TheemergingnewJavadevicesarestreamlinedsystemsthatexploitnetworkserversformuchoftheirprocessingpower,storage,content,rmationfromnumeroussourcesinaconsistent,enterprise-widefashionthroughtheuseoftheJMIAPI.7JavainIndustrialSettingsManypeopleknowJavaonlyasatoolontheWorldWideWebthatenablessitestoperformsomeoftheirfancierfunctionssuchasinteractivityandanimation.However,theactualusesforJavaaremuchmorewidespread.SinceJavaisanobject-orientedlanguage,thetimeneededforapplicationdevelopmentisminimal.Inaddition,Javasautomaticmemorymanagementandlackofpointersremovesomeleadingcausesofprogrammingerrors.Mostimportantly,applicationdevelopersdonotneedtocreatedifferentversionsofthesoftwarefordifferentplatforms.TheadvantagesavailablethroughJavahaveevenfoundtheirwayintohardware.TheemergingnewJavadevicesarestreamlinedsystemsthatexploitnetworkserversformuchoftheirprocessingpower,storage,content,andadministration.BenefitsofJavaThebenefitsofJavatranslateacrossmanyindustries,andsomearespecifictothecontrolandautomationenvironment.Javasabilitytorunonanyplatformenablestheorganizationtomakeuseoftheexistingequipmentwhileenhancingtheapplication.IntegrationWithfewexceptions,applicationsrunningonthefactoryfloorwereneverintendedtoexchangeinformationwithsystemsintheexecutiveoffice,butmanagershaverecentlydiscoveredtheneedforthattypeofinformation.BeforeJava,thatoftenmeantbringingtogetherdatafromsystemswrittenondifferentplatformsindifferentlanguagesatdifferenttimes.Integrationwasusuallydoneonapiecemealbasis,onceitworked,wasuniquetothetwoapplicationsitwastyingtogether.Additionalintegrationrequireddevelopingabrandnewsystemfromscratch,raisingthecostofintegration.ScalabilityAnotherbenefitofJavaintheindustrialenvironmentisitsscalability.Evenwheninternalcompatibilityisnotanissue,companiesoftenfacedifficultieswhensupplierswithwhomtheyshareinformationhaveincompatiblesystems.Thisbecomesmoreofaproblemassupply-chainmanagementtakesonamorecriticalrolewhichrequiresmanufacturerstointeractmorewithoffshoresuppliersandclients.Thegreatestefficiencycomeswhenallsystemscancommunicatewitheachotherandshareinformationseamlessly.SinceJavaissoubiquitous,i8toftensolvestheseproblems.DynamicWebPageDevelopmentJavahasbeenusedbybothlargeandsmallorganizationsforawidevarietyofapplicationsbeyondconsumerorientedwebsites.Sandia,amultiprogramlaboratoryoftheU.S.DepartmentofEnergysNationalNuclearSecurityAdministration,hasdevelopedauniqueJavaapplication.Thelabwastaskedwithdevelopinganenterprise-wideinventorytrackingandequipmentmaintenancesystemthatprovidesdynamicWebpages.ConclusionOpenstandardshavedriventhee-businessrevolution.Ase-businesscontinuestodevelop,variouscomputingtechnologieshelptodriveitsevolution.TheJavaprogramminglanguageandplatformhaveemergedasmajortechnologiesforperforminge-businessfunctions.thetimeneededforapplicationdevelopmentisminimal.Javaalsoencouragesgoodsoftwareengineeringpracticeswithclearseparationofinterfacesandimplementationsaswellaseasyexceptionhandling.Javasautomaticmemorymanagementandlackofpointersremovesomeleadingcausesofprogrammingerrors.TheadvantagesavailablethroughJavahavealsofoundtheirwayintohardware.TheemergingnewJavadevicesarestreamlinedsystemsthatexploitnetworkserversformuchoftheirprocessingpower,storage,content,andadministration.9中文翻译JavaScript的权威指南JavaScript是一种Web编程语言。绝大多数现代网站都使用JavaScript,所有现代web浏览器在台式电脑,游戏机,平板电脑和智能手机都包含JavaScript解释器,使JavaScript成为历史上最普遍使用的编程语言。JavaScript是所有Web开发人员必须学习的三位一体的技术的一部分,:HTML指定网页的内容,CSS指定网页的描述，而JavaScript来指定网页的行为。如果你早已经熟悉其他编程语言,它可以帮助你知道JavaScript是一个高层次、动态、类型化解释编程语言,是适合面向对象和函数式编程风格。JavaScript语法来自Java,其一级函数从计划,从自我及其基于原型的继承。但是你不需要知道任何的语言,或熟悉这些术语,使用这本书和学习JavaScript。JavaScript一名实际上有些令人误解的。除了表面的语法相似,JavaScript与Java编程语言完全不同。并且JavaScript早已超越了其脚本语言根成为一个健壮的、高效的通用语言。最新版本的语言(请参阅侧栏)定义了超大规模软件开发的新特性。词汇结构一种编程语言的词法结构是基本规则的设定，这种基本规则指定你如何用那种语言编写程序。这是一种语言最低级别的语法;它指定诸如变量名称是什么样子的,注释分隔符字符,以及一个程序语句怎样与下一个分开。这个简短的章节记载了JavaScript的词法结构。类型、值和变量计算机程序通过操纵值来工作,如数字3.14或文本“HelloWorld。”这种类型可以表示和操作编程语言的值被称为类型,和一个编程语言的最基本的特征是它所支持的类型。当一个程序需要为将来使用保留价值,它分配值和允许的值是通过名称引用。,变量的工作方式是另一个任何编程语言的基本特征。本章解释了类型、值和变量在JavaScript。JavaScript类型可分为两类:基本类型和对象类型。JavaScript的基本类型包括数字、文本字符串(字符串),布尔值(称为布尔)。这一章的很大一部分致力于详细解释JavaScript的数字类型和字符串类型。特殊的JavaScript值null值和未定义值是基本值,但它们并不是数字、字符串、或布尔值。每个值通常被认为是它自己的特殊类型的唯一成员。那些既不是一个数字,也不是一个字符串,一个布尔或null或未定义的任何JavaScript值是一个对象。一个对象(即类型对象的成员)是一个集合的属性,每个属性都有一个名称和一个值(原始值,如数字或字符串,或一个对象)。表达式和运算符一个表达式是一个JavaScript短语，它的JavaScript解释器可以评估产生一个值。在你的程序中，一个逐字嵌入的常数是一种非常简单的表达式。一个变量名也是一个简单的表达式,计算结果为任何赋给该变量的值。复杂的表达式是由简单的表达式构成的。一个数组访问的表达式,例如,由一个数组的表达式紧随其后的是一个开放的方括号,一个整数的表达式和一个闭合的方括号组成的表达式。这种新的、更复杂的表达式计算的值存储在指定的数组的指定的索引。同样,一个函数调用表达式由一个函数对象10的表达式和零个或多个作为函数的参数的附加表达式构成。主要表达式最简单的表达式,称为主要表达式,是单独存在的，不再包括其他任何更简单的表达式。在JavaScript，主要表达是常数或文字值,某些语言关键字,和变量引用。字面值是直接嵌入在你的程序中的常量值。一些JavaScript的保留字是主要表达式：:例如：true,false,null,this我们已经学习过了true,false,和null。与其他的关键词不同,thi