JavaScript程序的动态行为分析外文翻译节选.docx

JavaScript程序的动态行为分析外文翻译节选.docx

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JavaScript程序的动态行为分析外文翻译节选

1800单词，1万英文字符，3600汉字

出处：

RichardsG,LebresneS,BurgB,etal.AnanalysisofthedynamicbehaviorofJavaScriptprograms[C]//AcmSigplanConferenceonProgrammingLanguageDesign&Implementation.ACM,2010:

1-12.

AnAnalysisoftheDynamicBehaviorofJavaScriptPrograms

GregorRichardsSylvainLebresneBrianBurgJanVitek

Abstract

TheJavaScriptprogramminglanguageiswidelyusedforwebprogrammingand,increasingly,forgeneralpurposecomputing.Assuch,improvingthecorrectness,securityandperformanceofJavaScriptapplicationshasbeenthedrivingforceforresearchintypesystems,staticanalysisandcompilertechniquesforthislanguage.Manyofthesetechniquesaimtoreigninsomeofthemostdynamicfeaturesofthelanguage,yetlittleseemstobeknownabouthowprogrammersactuallyutilizethelanguageorthesefeatures.Inthispaperweperformanempiricalstudyofthedynamicbehaviorofacorpusofwidely-usedJavaScriptprograms,andanalyzehowandwhythedynamicfeaturesareused.WereportonthedegreeofdynamismthatisexhibitedbytheseJavaScriptprogramsandcomparethatwithassumptionscommonlymadeintheliteratureandacceptedindustrybenchmarksuites.

Keywords：

DynamicBehavior,ExecutionTracing,DynamicMetrics,ProgramAnalysis,JavaScript

1.Introduction

JavaScriptisanobject-orientedlanguagedesignedin1995byBrendanEichatNetscapetoallownon-programmerstoextendwebsiteswithclient-sideexecutablecode.UnlikemoretraditionallanguagessuchasJava,C#orevenSmalltalk,itdoesnothaveclasses,anddoesnotencourageencapsulationorevenstructuredprogramming.InsteadJavaScriptstrivestomaximizeflexibility.JavaScript’ssuccessisundeniable.Asadatapoint,itisusedby97outoftheweb’s100mostpopularsites.2Thelanguageisalsobecomingageneralpurposecomputingplatformwithofficeapplications,browsersanddevelopmentenvironmentsbeingdevelopedinJavaScript.Ithasbeendubbedthe“assemblylanguage”oftheInternetandistargetedbycodegeneratorsfromthelikesofJavaandScheme.Inresponsetothissuccess,JavaScripthasstartedtogarneracademicattentionandrespect.Researchershavefocusedonthreemainproblems:

security,correctnessandperformance.SecurityisarguablyJavaScript’smostpressingproblem:

anumberofattackshavebeendiscoveredthatexploitthelanguage’sdynamism（mostlytheabilitytoaccessandmodifysharedobjectsandtoinjectcodeviaeval）.Researchershaveproposedapproachesthatmarrystaticanalysisandruntimemonitoringtopreventasubsetofknownattacks.Anotherstrandofresearchhastriedtoinvestigatehowtoprovidebettertoolsfordevelopersforcatchingerrorsearly.Beingaweaklytypedlanguagewithnotypedeclarationsandonlyrun-timecheckingofcallsandfieldaccesses,itisnaturaltotrytoprovideastatictypesystemforJavaScript.Finally,aftermanyyearsofneglect,modernimplementationsofJavaScripthavestartedtoappearwhichusestateoftheartjust-in-timecompilationtechniques.

2.MotivationandRelatedWork

TheoriginalimpetusforourinterestinJavaScriptwastoassessthefeasibilityofastatictypesystemabletosuccessfullyandmeaningfullytypecheckexistingJavaScriptprograms.OtherdynamiclanguagessuchasSchemehavehadrecentsuccessintroducinggradualtypingsystems,buttheyhavestoppedshortoftypecheckingobject-orientedextensions（implementedbymacrosinScheme）.ForJavaScript,Andersonetal.proposedatypesystemwithdefiniteandpotentialtypes,whileHeideggerandThiemannfollowinguponsomeoftheirearlierworkproposerecencytypesin,andFurretal.proposedarelatedsystemforDRuby.Whileallofthesetypesystemsacknowledgesomeminorsimplificationstothetargetlanguage,theyrelyonfairlysimilarassumptions.Forinstance,Thiemannwrites:

“Usually,nofurtherpropertiesaredefinedaftertheinitializationandthetypeofthepropertiesrarelychanges.”

CommonAssumptionsaboutthedynamicbehaviorofJavaScript.

Weproceedtoenumeratetheexplicitandimplicitassumptionsthatarecommonlyfoundintheliteratureandinimplementations.

1.Theprototypehierarchyisinvariant.Theassumptionthattheprototypehierarchydoesnotchangeafteranobjectiscreatedissocentraltothetypesystemworkthatchosetonotevenmodelprototypes.Researchonstaticanalysistypicallydoesnotmentionprototypeupdates.Yet,anymodificationtotheprototypehierarchycanpotentiallyimpactthecontrolflowgraphoftheapplicationjustaswellasthetypesofaffectedobjects.

2.Propertiesareaddedatobjectinitialization.Folkloreholdsthatthereissomethingakintoan“initializationphase”indynamiclanguageswheremostofthedynamicactivityoccursandafterwhichtheapplicationismostlystatic.ForJavaScriptthisisembodiedbytheassumptionthatmostchangestothefieldsandmethodsofobjectsoccuratinitialization,andthusthatitisreasonabletoassignanalmostcompletetypetoobjectsatcreation,leavingasmallnumberofpropertiesaspotential.

3.Propertiesarerarelydeleted.Removalofmethodsorfieldsisdifficulttoccommodateinatypesystemasitpermitsnonmonotonicevolutionoftypesthatbreakssubtypingguaranteesusuallyenforcedinmoderntypedlanguages.Ifdeletionisanexceptionaloccurrence（andonethatcanbepredicted）,onecouldusepotentialtypesforpropertiesthatmaybedeletedinthefuture.But,thiswouldreducethebenefitsofhavingatype.

systeminthefirstplace,whichisprobablywhyrelatedworkchoosestoforbidit.Staticanalysisapproachesareusuallyabitmoretoleranttoimprecisionandcanhandledeletes,butwehavenotfoundanyexplanationofitshandlinginexistingdataflowanalysistechniques.

4.Theuseofevalisinfrequentanddoesnotaffectsemantics.Theuseofevalonarbitrarystringshasthepotentialofinvalidatinganyresultsobtainedbystaticanalysisorstatictypechecking.Thusmanyworkssimplyignoreit,whileotherassumethatusesareeithertrivialorrelatedtodeserializationusingtheJSONprotocol.

5.Declaredfunctionsignaturesareindicativeoftypes.TypesystemsforJavaScripttypicallyassumethatthedeclaredarityofafunctionisrepresentativeofthewayitwillbeinvoked.ThisisnotnecessarilythecasebecauseJavaScriptallows

callswithdifferentarities.

6.Programsizeismodest.SomepapersjustifyveryexpensiveanalyseswiththeexplicitassumptionthathandwrittenJavaScriptprogramsaresmall,andothersimplicitlyrelyonthisastheypresentanalyseswhichwouldnotscaletolargesystems.

7.Call-sitedynamismislow.SomeJavaScriptimplementationssuchasGoogleV8relyonwell-knownimplementationtechniquestooptimizeJavaScriptprogramssuchascreatingclasses（intheJavasense）forobjectsandinlinecaches.ThesetechniqueswillleadtogoodperformanceonlyifthebehaviorofJavaScriptisbroadlysimilartothatofotherobject-orientedlanguages

8.Executiontimeisdominatedbyhotloops.Trace-basedJustin-timecompilerssuchasTraceMonkeyrelyonthetraditionalassumptionthatexecutiontimeisdominatedbysmallloops.

9.IndustrybenchmarksarerepresentativeofJavaScriptworkloads.StandardenchmarksuitessuchasSunSpider,DromaeoandV8,areusedtotuneandcompareJavaScriptimplementationsandtoevaluatetheaccuracyofstaticanalysistechniques.ButconclusionsobtainedfromuseofthosebenchmarksareonlymeaningfuliftheyaccuratelyrepresenttherangeofJavaScriptworkloadsinthewild.

Thegoalofthispaperistoprovidesupportingevidencetoeitherconfirmorinvalidatetheseassumptions.Wearenotdisputingthevalidityofpreviousresearch,asevenifacoupleoftheaboveassumptionsprovedtobeunfounded,previousworkcanstillserveasausefulstartingpointforhandlingfullJavaScript.Butwedowanttohighlightlimitationstowidespreadadoptionofexistingtechniquesandpointtochallengesthatshouldbeaddressedinfutureresearch.

RelatedWork.Untilnow,tothebestofourknowledge,therehasbeennostudyofthedynamicbehaviorofJavaScriptprogramsofcomparabledepthorbreadth.Ratanaworabhanetal.haveperformedasimilarstudyconcurrentlytoourown,anditsresultsaresimilartoours.TherehavebeenstudiesofJavaScript’sdynamicbehaviorasitappliestosecurity,butthebehaviorsstudiedwererestrictedtothoseparticularlyrelevanttosecurity.WeconductedasmallscalestudyofJavaScriptandreportedpreliminaryresultsin,andthoseresultsareconsistentwiththenewresultspresentedhere.HolknerandHarlandhaveconductedastudyoftheuseofdynamicfeatures（additionanddeletionoffieldsandmethods）inthePythonprogramminglanguage.Theirstudyfocusedonasmallersetofprogramsandconcludedthatthereisaclearphasedistinction.Intheircorpusdynamicfeaturesoccurmostlyintheinitializationphaseofprogramsandlesssoduringthemaincomputation.OurresultssuggestthatJavaScriptismoredynamicthanPythoninpractice.Therearemanystudiesoftheruntimeuseofselectedfeaturesofobject-orientedlanguages.Forexample,Garretetal.reportedonthedynamismofmessagesendsinSelf,Calderetal.characterizedthedifferenceofbetweenCandC++programsin,andTemporoetal.studiedtheusageofinheritanceinJavain.Thesepreviouspapersstudyingreatdetailoneparticularaspectofeachlanguage.Inthisparticularwork,westriveforanoverviewofJavaScript,andleavedetailedanalysisforfuturework.Finally,wewereinspiredbytheworkofDufouretal.andtheirrigorousframeworkfordiscussingruntimemetricsforJava.

3.TracingandAnalysisInfrastructure

Thetracing