LearningNode.jsfor.NETDevelopers

TableofContents

LearningNode.jsfor.NETDevelopersCreditsAbouttheAuthorAbouttheReviewerwww.PacktPub.com

eBooks,discountoffers,andmoreWhysubscribe?

PrefaceWhatthisbookcoversWhatyouneedforthisbookWhothisbookisforConventionsReaderfeedbackCustomersupport

DownloadingtheexamplecodeDownloadingthecolorimagesofthisbookErrataPiracyQuestions

1.WhyNode.js?WhatisNode.js?

UnderstandingtheNode.jsexecutionmodelNon-blockingEvent-drivenSingle-threaded

IntroducingtheNode.jsecosystemWhyJavaScript?

AclearcanvasFunctionalnatureAbrightfuture

WhentouseNode.jsWritingwebapplicationsIdentifyingotherusecasesWhynow?

Summary2.GettingStartedwithNode.js

InstallingandrunningNode.jsChoosinganeditorUsinganapplicationframework

GettingstartedwithExpressExploringourExpressapplication

UnderstandingExpressroutesandviewsUsingnodemonforautomaticrestartsCreatingmodularapplicationswithExpressBootstrappinganExpressapplicationUnderstandingExpressmiddleware

ImplementingerrorhandlingUsingExpressmiddleware

Summary3.AJavaScriptPrimer

IntroducingJavaScripttypesJavaScriptprimitivetypes

Functionalobject-orientedprogrammingFunctionalprogramminginJavaScriptUnderstandingscopesinJavaScript

StrictmodeObject-orientedprogramminginJavaScript

ProgrammingwithoutclassesCreatingobjectswiththenewkeyword

ProgrammingwithclassesClass-basedinheritance

Summary4.IntroducingNode.jsModules

OrganizingyourcodebaseJavaScriptmodulesystems

CreatingmodulesinNode.jsDeclaringamodulewithanameanditsownscopeDefiningfunctionalityprovidedbythemoduleImportingamoduleintoanotherscript

Definingadirectory-levelmoduleImplementinganExpressmiddlewaremoduleSummary

5.CreatingDynamicWebsitesHandlinguser-submitteddataCommunicatingviaAjaxImplementingotherdataoperations

ListingdatainviewsIssuingadeleterequestfromtheclientSplittingupExpressviewsusingpartials

Summary6.TestingNode.jsApplications

WritingasimpletestinNode.jsStructuringthecodebasefortestsWritingBDD-styletestswithMocha

Resettingstatebetweentests

UsingChaiforassertionsCreatingtestdoubles

CreatingtestdoublesusingSinon.JSTestinganExpressapplication

SimplifyingtestsusingSuperAgentFull-stacktestingwithPhantomJSSummary

7.SettingupanAutomatedBuildSettingupanintegrationserver

SettingupapublicGitHubrepositoryBuildingaprojectonTravisCI

AutomatingthebuildprocesswithGulpRunningtestsusingGulp

CheckingcodestylewithESLintAutomaticallyfixingissuesinESLintRunningESLintfromGulp

GatheringcodecoveragestatisticsRunningintegrationtestsfromGulpSummary

8.MasteringAsynchronicityUsingthecallbackpatternforasynchronouscode

ExposingthecallbackpatternConsumingasynchronousinterfaces

WritingcleanerasynchronouscodeusingpromisesImplementingpromise-basedasynchronouscode

ConsumingthepromisepatternParallelisingoperationsusingpromises

CombiningasynchronousprogrammingpatternsSummary

9.PersistingDataIntroducingMongoDB

WhychooseMongoDB?ObjectmodelingJavaScriptScalability

GettingstartedwithMongoDBUsingtheMongoDBshell

UsingMongoDBwithExpressPersistingobjectswithMongooseIsolatingpersistencecodeDependencyinjectioninNode.jsProvidingdependenciesRunningdatabaseintegrationtestsonTravisCI

IntroducingRedis

WhyuseRedis?InstallingRedisUsingRedisasakey-valuestoreStoringstructureddatainRedis

BuildingauserrankingsystemwithRedisUsingRedisfromNode.js

Testingwithredis-jsImplementinguserrankingswithRedisMakinguseoftheusersservice

AnoteonsecuritySummary

10.CreatingReal-timeWebAppsUnderstandingoptionsforreal-timecommunicationIntroducingSocket.IO

ImplementingachatroomwithSocket.IOScalingreal-timeNode.jsapplications

UsingRedisasabackendIntegratingSocket.IOwithExpressDirectingSocket.IOmessagesTestingSocket.IOapplicationsOrganizingSocket.IOapplications

Exposingreal-timeupdatestothemodelOrganizingSocket.IOapplicationsusingnamespacesPartitioningSocket.IOclientsusingrooms

Summary11.DeployingNode.jsApplications

WorkingwithHerokuSettingupaHerokuaccountandtoolingRunninganapplicationlocallywithHerokuDeployinganapplicationtoHerokuWorkingwithHerokulogs,config,andservices

SettingupMongoDBSettingupRedis

DeployingfromTravisCISettingencryptedTravisCIenvironmentvariables

InstallingRubyCreatinganencryptedenvironmentvariable

FurtherresourcesSummary

12.AuthenticationinNode.jsIntroducingPassport

ChoosinganauthenticationstrategyUnderstandingthird-partyauthentication

UsingExpresssessions

SpecifyingasessionsecretDecidingwhenthesessiongetssavedUsingalternativesessionstoresUsingsessionmiddleware

ImplementingsocialloginSettingupaTwitterapplicationConfiguringPassportPersistinguserdatawithRedisConfiguringPassportwithpersistenceHidingfunctionalityfromunauthenticatedusersIntegrationtestingwithPassport

AllowinguserstologoutAddingotherloginprovidersSummary

13.CreatingJavaScriptPackagesWritinguniversalmodules

ComparingNode.jsandRequireJSSupportingthebrowserenvironmentUsingAMDmoduleswithRequireJSIsomorphicJavaScript

WritingnpmpackagesDefiningannpmpackage

PublishingapackagetonpmRunningautomatedclientsonthewebReleasingastandalonetooltonpm

UsingNode.jsmodulesinthebrowserControllingBrowserify'soutput

Summary14.Node.jsandBeyond

UnderstandingNode.jsversioningAbriefhistoryofNode.jsIntroducingtheNode.jsLTSschedule

UnderstandingECMAScriptversioningExploringECMAScript2015

UnderstandingES2015modulesUsingsyntaximprovementsfromES2015

Thefor...ofloopThespreadoperatorandrestparametersDestructuringassignment

IntroducinggeneratorsIntroducingECMAScript2016GoingbeyondJavaScript

Exploringcompile-to-JavaScriptlanguagesTypeScript

CoffeeScriptAndbeyond...

IntroducingatrueassemblylanguageforthewebUnderstandingasm.jsUnderstandingWebAssembly

JavaScriptandASP.NETExploring.NETCore

Definingprojectstructurein.NETCoreManagingdependenciesin.NETCoreBuildingwebapplicationsinASP.NETCore

IntegrationwithJavaScriptServer-sideJavaScriptintegrationwith.NET

SummaryIndex

LearningNode.jsfor.NETDevelopers

LearningNode.jsfor.NETDevelopersCopyright©2016PacktPublishing

Allrightsreserved.Nopartofthisbookmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,withoutthepriorwrittenpermissionofthepublisher,exceptinthecaseofbriefquotationsembeddedincriticalarticlesorreviews.

Everyefforthasbeenmadeinthepreparationofthisbooktoensuretheaccuracyoftheinformationpresented.However,theinformationcontainedinthisbookissoldwithoutwarranty,eitherexpressorimplied.Neithertheauthor,norPacktPublishing,anditsdealersanddistributorswillbeheldliableforanydamagescausedorallegedtobecauseddirectlyorindirectlybythisbook.

PacktPublishinghasendeavoredtoprovidetrademarkinformationaboutallofthecompaniesandproductsmentionedinthisbookbytheappropriateuseofcapitals.However,PacktPublishingcannotguaranteetheaccuracyofthisinformation.

Firstpublished:June2016

Productionreference:1170616

PublishedbyPacktPublishingLtd.

LiveryPlace

35LiveryStreet

BirminghamB32PB,UK.

ISBN978-1-78528-009-2

www.packtpub.com

CreditsAuthor

HarryCummings

Reviewer

DavidSimons

CommissioningEditor

KunalParikh

AcquisitionEditor

RahulNair

ContentDevelopmentEditor

TrushaShriyan

TechnicalEditor

JayeshSonawane

CopyEditor

SafisEditing

ProjectCoordinator

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Proofreader

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Indexer

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Graphics

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ProductionCoordinator

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CoverWork

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AbouttheAuthorHarryCummingshasbeenworkinginsoftwaredevelopmentfor8years,andforthepastfewyears,hehasperformedtheroleoftechnicalleadacrossavarietyofprojectsforvariedclients.Hehas,inthepast,alsoworkedasadeveloper,projectmanager,andconsultant.Thisgiveshimanexcellentall-roundviewoftheroleofatechnicalleadanditsrelationshipwithotherrolesaswellasinsightintoeverystageofprojectdelivery,frominitialanalysistolong-termmaintenance.

HarryhasextensiveexperienceinC#/.NET,JavaandScala,andJavaScript/Node.js.Hecontinuestoworkdirectlywiththesetechnologiesonaregularbasisintheteamsthatheleads.Hisbroaderinterestsandexpertiselieinsharingandnurturingsoftwaredevelopmentbestpracticesthroughtrainingandmentoring.HehasappearedatconferencessuchasNDCLondonandSDDConf,speakingaboutdiversetopics,rangingfromintroductoryNode.jsthroughtoautomatedteststrategiesandlong-termprojectmaintainability.

AbouttheReviewerDavidSimonsisaLondon-basedsoftwareconsultant.Heisfamiliarwithawiderangeoftools,havinghelpedclientssuchastheBBCandNewsInternationaldeliverwebsolutionsinarangeoflanguages,including.NET,Java,andfull-stackJavaScript.Heshareshisinsightsaroundtheseandhisbackgroundinstatisticsresearchatarangeofconferences,includingNDCandJSConf.

Asof2016,heworkswithLondon-basedconsultancyGraphAwaretoadvocateandconsultontheuseofgraphdatabasesinmodernapplications.

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PrefaceThepurposeofthisbookistohelp.NETorJavadevelopersmaketheleaptoNode.js.Youmayhavesomewebdevelopmentexperience,andperhapsyou'vewrittensomebrowser-basedJavaScriptinthepast.ItmightnotbeobviouswhyanyonewouldwanttotakeJavaScriptoutofthebrowseranduseitforserver-sidedevelopment.However,thisisexactlywhatNode.jsdoes.What'smore,Node.jshasbeenaroundforlongenoughnowtohavematuredasaplatform,andhassustaineditsimpressivegrowthinpopularitywellbeyondanyperiodthatcouldbeattributedtoinitialhypeoveranewtechnology.

ThefirstobjectiveofthisbookthenistoexplainwhyNode.jsisacompellingtechnologythat'sworthlearningmoreabout.ThefirstfewchaptersintroduceNode.jswiththisinmind,quicklygetyouupandrunningwithNode.js,andprovideanimportant(re)introductiontotheJavaScriptlanguagetosetyouontherighttrack.

ThemainpartofthisbookwillthentakeyouthroughaworkedexampleofbuildingupaNode.jsweb-applicationstepbystep.Intheprocess,we'llillustratealltheimportanttoolsandtechniquesrequiredforreal-worlddevelopmentprojectsinNode.js.TheaimistomakethemostofyourexistingdevelopmentexpertisetoallowyoutoquicklyreachthesamelevelofbestpracticesandprofessionalismwithNode.js.

ThefinalchaptersofthebookshowhowtouseNode.jsforotherpurposesoutsideofwebapplicationsandhowtocontinuelearningNode.jsandexploringtheecosystemaroundit.We'llalsoseehowyoucanuseNode.jsalongside.NETandbenefitfromapplyingyourprogrammingskillsacrossbothtechnologies.

WhatthisbookcoversChapter1,WhyNode.js?,introducesNode.jsasaprogrammingplatform.ItcoverstheexecutionmodelofNode.js,particularlyhowitdiffersfrom.NETandJava,andtheusecasesinwhichthesedifferencesbecomestrengths.ThischapteralsodiscussesthesuitabilityofJavaScriptasadevelopmentlanguage.

Chapter2,GettingStartedwithNode.js,divesstraightintocreatingaNode.jsapplication.Inthischapter,youwillinstallNode.js,chooseacodeeditor,andsetupaminimalwebapplicationproject.You'llalsolearnsomeimportantcommand-linetoolsforworkingwithNode.js.

Chapter3,AJavaScriptPrimer,introducesthemostimportantthingstoknowwhenprogramminginJavaScript.ItdescribestheJavaScripttypesystemanditsparticularflavoroffunctionalobject-orientedprogramming,includingprototype-basedinheritance.ThischapteralsocoversafewkeygotchasandJavaScriptlanguagequirks.

Chapter4,IntroducingNode.jsModules,explainshowtostructureJavaScriptapplicationsusingmodules.ItintroducestheNode.jsmodulesystemandshowsyouhowtousethistoorganiseyourapplication'scode.

Chapter5,CreatingDynamicWebsites,expandsontheexamplesfromthepreviouschaptertobuildafunctioningwebapplication.You'lladdaJSONAPIanddynamicviewstoyourapplicationandcommunicatebetweentheclientandserverusingAjax.

Chapter6,TestingNode.jsApplications,showsyouhowtowriteautomatedtestsinJavaScriptandNode.js.ItintroducesanumberoftoolsandlibrariesforwritingandrunningtestsinJavaScript,andguidesyouthroughwritingavarietyofunittestsandintegrationtestsforyourapplication.

Chapter7,SettingupanAutomatedBuild,coversbuildautomationandcontinuousintegrationinNode.js.You'llsetupaCIserverandtaskrunnerforyourapplication,addingautomatedtaskstoruntests,executestaticanalysis,andassesscodecoverage.

Chapter8,MasteringAsynchronicity,introducesdifferentpatternsforasynchronousprogramminginJavaScript.You'llapplythesetoyourownapplicationandmakethemostofJavaScriptlanguagefeaturesandlibrariesforsimplifyingasynchronouscode.

Chapter9,PersistingData,explainspersistentdatastoresthatcanbeusedwithNode.js.ItintroducesMongoDBandRedis,explainingtheirdifferentdatamodelsandtheirusecases.You'llintegratebothofthesedatastoreswithyourNode.jsapplication.

Chapter10,CreatingReal-timeWebApps,showshowtoimplementreal-timetwo-waycommunicationbetweentheclientandtheserver.You'llusetheSocket.IOlibrarytoaddreal-timefunctionalityintoyourapplication.You'llalsoseehowtowritetestsforthisfunctionalityand

howtowritescalablereal-timeapplicationsusingRedisasabackend.

Chapter11,DeployingNode.jsApplications,demonstrateshowtogetaNode.jsapplicationontotheWeb.You'lldeployyourapplicationtoafreecloud-hostingprovider.You'llseehowtoconfiguredatastoresandhowtouseremoteserverlogsfordebugging.

Chapter12,AuthenticationinNode.js,coversauthenticationforNode.jswebapplications.You'llimplementauthenticationusingthird-partyproviders,integratethiswithyourapplication,andshowdifferentcontenttologged-inandlogged-outusers.

Chapter13,CreatingJavaScriptPackages,explainshowtocreatestandaloneJavaScriptpackagesforusebyothers.You'llseehowtowriteuniversalJavaScriptlibrariesthatcanrunonboththeclientandtheserver,andhowtowriteastandalonecommand-lineapplicationusingNode.js.

Chapter14,Node.jsandBeyond,putsthecontentofthisbookinawidercontext.ItexplainshowNode.jsandJavaScriptarecontinuingtoevolve,soyoucanbepreparedforandtakeadvantageofupcomingchanges.ItcoverssomealternativeprogramminglanguagesforNode.jsandtheWeb,andhowtheserelatetoJavaScript.ItdiscusseshowsomeoftheprinciplesfromNode.jscanbeappliedto.NETprogramming,andillustrateshowtheseareparticularlyvisiblein.NETCore(thenewversionof.NET).ItalsoshowshowyoucanuseNode.jstogetherwith.NETtogainthebestofbothworlds.

WhatyouneedforthisbookAllofthetoolsandservicesusedinthisbookareavailableforfreeonline.Mostoftheworkedexamplesrequireanactivewebconnectionatsomepoint.Togetstarted,youneednothingmorethanaconsole,awebbrowser,andpermissiontoinstallnewsoftwareonyourmachine.Tosupportdeveloperscomingfroma.NETbackground,someoftheconsolelistingsorexamplestepsinthisbookuseWindowsconventions(forexample,backslashesinpaths).NoneoftheexamplesdependonWindowsspecificallythough.YoucanworkthroughthisbookonWindows,MacOSX,orLinux.

WhothisbookisforThisbookisfor.NETorJavadeveloperswhoareinterestedinlearningNode.js.NopriorexperiencewithNode.jsisexpected.Youmighthavewrittensomeclient-sideJavaScriptbefore,butthisisnotrequired.ThemainworkedexampleinthisbookisaNode.jswebapplication.Webdevelopmentexperiencein.NETorJavawillbehelpful,butit'snotnecessarytohaveexperiencewithanyparticularapplicationlibraryorframework.

ConventionsInthisbook,youwillfindanumberoftextstylesthatdistinguishbetweendifferentkindsofinformation.Herearesomeexamplesofthesestylesandanexplanationoftheirmeaning.

Codewordsintext,databasetablenames,foldernames,filenames,fileextensions,pathnames,dummyURLs,userinput,andTwitterhandlesareshownasfollows:"ES2015introducestheletkeywordfordeclaringvariables."

Ablockofcodeissetasfollows:

<!DOCTYPEhtml>

<html>

<head>

<title>{{title}}</title>

<linkrel='stylesheet'href='/stylesheets/style.css'/>

</head>

<body>

<h1>{{title}}</h1>

<p>Welcometo{{title}}</p>

</body>

</html>

Whenwewishtodrawyourattentiontoaparticularpartofacodeblock,therelevantlinesoritemsaresetinbold:

/*GEThomepage.*/

router.get('/',function(req,res,next){

res.render('index',{title:'Express',name:'World'});

});

Anycommand-lineinputoroutputiswrittenasfollows:

>npminstall–gnodemon

Newtermsandimportantwordsareshowninbold.Wordsthatyouseeonthescreen,forexample,inmenusordialogboxes,appearinthetextlikethis:"ClickingtheNextbuttonmovesyoutothenextscreen."

Note

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Chapter1.WhyNode.js?Node.jsisstillrelativelynewcomparedtoplatformssuchas.NETandJava,buthasbecomeverypopularinashorttime,andhasevenstartedinfluencingtheseplatforms.Thisisthankstoitsdistinctiveprogrammingmodel,extensiveecosystem,andpowerfultooling.

ThesefactorsmakeNode.jsacompellingalternativetootherplatforms.Theycanalsomakeitintimidating.Itsdistinctiveprogrammingmodelmayseemquitealiencomparedtootherplatforms.Thesheerrangeofavailablelibrariesandtoolscanbebewildering.

ThisbookwillguideyouthroughNode.jssoyoucanstartusingitinyourapplications.ItwillhelpyoutounderstandNode.js,navigateitsecosystem,andleverageyourexistingdevelopmentskillsinthisnewenvironment.

Inthischapter,wewillcoverthefollowingtopics:

IntroducingtheNode.jsplatformSeeinghowitsexecutionmodelworksExploringtheNode.jsecosystemLookingatJavaScriptasalanguagechoiceConsideringtherangeofusecasesforNode.js

WhatisNode.js?Node.jsconsistsofaJavaScriptenginetogetherwithlow-levelAPIsforcoreserver-sidefunctionality.TheexecutionengineisthesameV8enginedevelopedfortheChromewebbrowser.Node.jstakesthisengineandembedsitinastandaloneapplicationthatcanrunJavaScriptoutsidethebrowser.

InNode.js,thestandardAPIsfoundinbrowserstosupportclient-sidewebdevelopment,suchastheDocumentObjectModel(DOM)andXMLHttpRequest,arenotpresent.Instead,thereareAPIstosupportgeneral-purposeapplicationdevelopment.ThesecoreAPIscoverlow-levelfunctionalitysuchasthefollowing:

NetworkingandsecurityAccessingthefilesystemDefiningandrequiringmodulesRaisingandconsumingeventsHandlingbinarydatastreamsCompressionUTF-8supportRetrievingbasicinformationabouttheOSManagingchildprocesses

SomeoftheseAPIsmayalreadybefamiliarfromdevelopingclient-sideJavaScript.Forexample,theTimersAPIexposesthefamiliarsetTimeoutandsetIntervalfunctions.

Node.jsalsoprovidesseveraltoolstohelpwiththedevelopmentprocess.Theseincludeconsolelogging,debugging,aRead-Eval-PrintLoop(REPL)(orinteractiveconsole),andbasicassertionsfortesting.

UnderstandingtheNode.jsexecutionmodelTheexecutionmodelofNode.jsfollowsthatofJavaScriptinthebrowser.Itisquitedifferentfromthatofmostgeneral-purposeprogrammingplatforms.

Statedformally,Node.jshasasingle-threaded,non-blocking,event-drivenexecutionmodel.Wewilldefineeachofthesetermsinthissection.

Non-blocking

Putsimply,Node.jsrecognizesthatmanyprogrammesspendmostoftheirtimewaitingforotherthingstohappen,forexample,slowI/Ooperationssuchasdiskaccessandnetworkrequests.

Node.jsaddressesthisbymakingtheseoperationsnon-blocking.Thismeansthatprogramexecutioncancontinuewhiletheyhappen.Forexample,thefilesystemAPI'sstatfunctionforretrievingstatisticsaboutafilemaybecalledasfollows:

fs.stat('/hello/world',function(error,stats){

console.log('Filelastupdatedat:'+stats.mtime);

});

Twoargumentsarepassedtothefs.statfunction:thenameofthefilethatweareinterestedin,andacallbackfunction.Thefs.statcallreturnsimmediately,returningcontrolofexecutiontothecurrentthreadbutnotreturningavalue.Iftherearefurthercommandsfollowingthefs.statcall,thesewillthenbeexecuted.Otherwise,thethreadisreleasedtoperformotherwork.Thecallbackfunctionisinvoked(thatis'calledback')onlyaftertheruntimehasfinishedcommunicatingwiththefilesystem.Theresultofthefilesystemoperationispassedintothecallbackfunction.

Thisnon-blockingapproachisalsocalledasynchronousprogramming.Otherplatformssupportthis(forexample,C#'sasync/awaitkeywordsand.NET'sTaskParallelLibrary).However,itisbakedintoNode.jsinawaythatmakesitsimpleandnaturaltouse.AsynchronousAPImethodsareallcalledinthesamewayasfs.stat.Theyalltakeacallbackfunctionthatgetspassederrorandresultarguments.

Event-driven

Theevent-drivennatureofNode.jsdescribeshowoperationsarescheduled.Intypicalproceduralenvironments,aprogramhasanentrypointthatexecutesasetofcommandsuntilcompletion,orentersaloopandperformssomeprocessingoneachiteration.

Node.jshasabuilt-ineventloop,whichisn'texposedtothedeveloper.Itisthejoboftheeventlooptodecidewhichpieceofcodetoexecutenext.Typically,thiswillbeacallbackfunctionthatisreadytoruninresponsetosomeotherevent.Forexample,afilesystemoperationmayhavecompleted,atimeoutmayhaveexpired,oranewnetworkrequestmayhavearrived.

Thisbuilt-ineventloopsimplifiesasynchronousprogrammingbyprovidingaconsistentapproach

andavoidingtheneedforapplicationstomanagetheirownscheduling.

Single-threaded

Thesingle-threadednatureofNode.jssimplymeansthatthereisonlyonethreadofexecutionineachprocess.Also,eachpieceofcodeisguaranteedtoruntocompletionwithoutbeinginterruptedbyotheroperations.Thisgreatlysimplifiesdevelopmentandmakesprogramseasiertoreasonabout.Itremovesthepossibilityforarangeofconcurrencyissues.Forexample,itisnotnecessarytosynchronize/lockaccesstosharedin-processstateasitisinJavaor.NET.Aprocesscan'tdeadlockitselforcreateraceconditionswithinitsowncode.Single-threadedprogrammingisonlyfeasibleifthethreadnevergetsblockedwaitingforlong-runningworktocomplete.Thus,thissimplifiedprogrammingmodelismadepossiblebythenon-blockingnatureofNode.js.

IntroducingtheNode.jsecosystemThebuilt-inNode.jsAPIsprovidealow-levelcoreforcreatingapplications.ApplicationstypicallyonlyuseasmallnumberoftheseAPIsdirectly.Theyoftenusethird-partylibrarymodulesthatprovidehigher-levelabstractionsforapplicationdevelopment.

Node.jshasitsownpackagemanager,npm.Thisissimilarto.NET'sNuGetorthepackagemanagementaspectsofJava'sMaven.ApplicationsspecifytheirdependenciesinasimpleJSONfile.

Thenpmregistryprovidesacentralrepositoryforpackages.Thisregistryhasgrownrapidlyandisalreadymuchlarger(intermsofnumberofavailablepackages)thanthecorrespondingrepositoriesforotherplatforms(seehttp://www.modulecounts.com/).Therearehundredsofthousandsofpackagesavailable,providingavastarrayoffunctionality.

Thenpmcommandlinetoolcanbeusedtodownloadpackagesandinstallnewones.Librarydependenciesareinstalledlocallytoeachapplication.Somepackagesprovidecommand-linetools,whichmaybeinstalledgloballyratherthanunderaspecificproject.

Manyframeworksavailableonnpmaresplitintoasmallextensiblecoreandanumberofcomposablemodules.Thisapproachmakesiteasytounderstandthelibrariesonwhichyourapplicationdepends,avoidingtheneedtoreasonaboutcomplexheavyweightframeworks.

Theconsistencyofcallingnon-blocking(asynchronous)APImethodsinNode.jscarriesthroughtoitsthird-partylibraries.Thisconsistencymakesiteasytobuildapplicationsthatareasynchronousthroughout.

WhyJavaScript?JavaScriptisalanguagethatcanseemunintuitivecomparedtootherpopularobject-oriented(OO)languages.Italsohasanumberofquirksandflawsthathavedrawncriticism(andoccasionalridicule).Itmightthenseemasurprisingchoiceoflanguageforanewprogrammingplatform.ThissectiondiscussesthefactorsthatmakeJavaScriptamoreappealingchoice.

AclearcanvasThesizeandcomplexityofJavaScriptispartofitsappeal.Thecorelanguageitself,whichdoesn'tincludeAPIssuchastheDOM,issmallandsimple.ThismakesiteasyforNode.jstoestablishitsownstylesandconventions.

ThenewAPIsprovidedbyNode.jsandtheconsistentapproachtoasynchronousprogrammingwouldn'tbepossibleinamorecomplexlanguagewithalargerpre-existingstandardclasslibrary.

FunctionalnatureJavaScriptwasfirstbuiltasaprogramminglanguageforclient-sidefunctionalityinthebrowser.Thismightnotmakeitanobviouschoiceforgeneral-purposeprogramming.

Infact,thesetwousecasesdohavesomethingimportantincommon.Userinterfacecodeisnaturallyevent-driven(forexample,bindingeventhandlerstobuttonclicks).Node.jsmakesthisavirtuebyapplyinganevent-drivenapproachtogeneral-purposeprogramming.

JavaScriptsupportsfunctionsasfirst-classobjects.Thismeansit'seasytocreatefunctionsdynamicallyandpassaroundreferencestothem.Thisfitsinwellwiththeasynchronous,non-blockingapproachofNode.js.Inparticular,it'seasytoexposeanduseAPIsbasedaroundcallbackfunctions.

AbrightfutureJavaScripthasreceivedalotofattentioninthelastseveralyearsasithasbecomemorewidelyusedforprovidingrichfunctionalityontheWeb.BrowservendorshaveputahugeamountofengineeringeffortintoimprovingtheperformanceofJavaScript.Node.jsbenefitsfromthisdirectlyviaitsuseofChrome'sV8engine.

TheJavaScriptlanguageitselfisundergoingsomemajorchangesforthebetter.TheECMAScript2015standard(previouslyknownasES6)representsthemostsignificantrevisionofthelanguageinitshistory.Itintroducesfeaturesthatmakethelanguagemoreintuitiveandlessverbose.ItalsoaddressesflawsthatJavaScripthasbeencriticizedforinthepast,removinggotchasandmakingprogramseasiertoreasonabout.

WhentouseNode.jsAsdiscussedearlierinthischapter,Node.jsrecognizesthatI/Oisabottleneckformanyapplications.Onmostprogrammingplatforms,threadswillwastetimeblockingonI/Ooperations.Thereareapproachesdeveloperscantaketoavoidthis,buttheseallinvolveaddingsomecomplexitytotheircode.InNode.js,theplatformitselfprovidesacompletelynaturalapproach.

WritingwebapplicationsTheflagshipusecaseforNode.jsisbuildingwebapplications.Theseareinherentlyevent-drivenasmostorallprocessingtakesplaceinresponsetoHTTPrequests.Also,manywebsitesdolittlecomputationalheavy-liftingoftheirown.TheytendtoperformalotofI/Ooperations:

StreamingrequestsfromtheclientTalkingtoadatabase,locallyoroverthenetworkPullingindatafromremoteAPIsoverthenetworkReadingfilesfromdisktosendbacktotheclient

ThesefactorsmakeI/Ooperationsalikelybottleneckforwebapplications.Thenon-blockingprogrammingmodelofNode.jsallowswebapplicationstomakethemostofasinglethread.AssoonasanyoftheseI/Ooperationsstarts,thethreadisimmediatelyfreetopickupandstartprocessinganotherrequest.ProcessingofeachrequestcontinuesviaasynchronouscallbackswhenI/Ooperationscomplete.Theprocessingthreadisonlykickingoffandlinkingtogethertheseoperations,neverwaitingforthemtocomplete.ThisallowsNode.jstohandleamuchhigherrateofrequestsperthreadthanotherplatforms.Youcanalsostillmakeuseofmultiplethreads(forexample,onmulti-coreCPUs)bysimplyrunningmultipleinstancesoftheNode.jsprocess.

IdentifyingotherusecasesThereareofcoursesomeapplicationsthatdon'tperformmuchI/OandaremorelikelytobeCPUbound.Node.jswouldbelesssuitableforcomputationally-intensiveapplications.Programsthatdoalotofprocessingofin-memorydataarelessconcernedaboutI/O.

WebapplicationsarenottheonlyI/O-heavyapplicationsthough.OtherclassesofprogramthatcouldbeagoodcandidateforNode.jsincludethefollowing:

ToolsthatmanipulatelargeamountsofdataondiskSupervisorprogramscoordinatingothersoftwareorhardwareNon-browserGUIapplicationsthatneedtorespondtouserinput

Node.jsisespeciallysuitableforglueapplicationsthatpulltogetherfunctionalityfromotherremoteservices.Theincreasingpopularityofmicroservicesasanarchitecturalpatternmakesthiskindofapplicationmorecommon.

Whynow?Node.jshasbeenaroundforseveralyears,butnowistheperfecttimetostartusingitifyouhaven'talready.

ThereleaseofNode.jsv4towardstheendof2015consolidatedtheproject'sgovernancemodelandheraldsNode.jscomingtomaturity.ItalsoallowstheprojecttokeepmoreuptodatewiththeV8engine.ThismeansthatNode.jscanbenefitmoredirectlyfromongoingdevelopmentonV8.Forexample,securityandperformanceimprovementstoV8willnowmaketheirwayintoNode.jsmuchsooner.

Asdiscussedearlierinthischapter,thereleaseoftheECMAScript2015standardmakesJavaScriptamuchmoreappealinglanguage.ItpullsinusefulfeaturesfromotherpopularOOlanguagesandresolvesanumberoflong-standingflawsinJavaScript.

Meanwhile,theecosystemofthirdpartylibrariesandtoolsaroundNode.jsandJavaScriptcontinuestogrow.Node.jsistreatedasafirst-classcitizenbymajorhostingplatforms.CompaniessuchasGoogleandMicrosoftarealsothrowingtheirweightbehindJavaScriptandrelatedtechnologies.

SummaryInthischapter,wehaveunderstoodNode.jsanditsdistinctiveexecutionmodel,exploredthegrowingecosystemaroundNode.jsandJavaScript,seenthereasonsforJavaScriptasalanguagechoice,anddescribedthekindsofapplicationthatcanbenefitfromNode.js.

NowthatyouknowhowNode.jsworksandwhentouseit,it'stimetodiveinandgetourfirstNode.jsapplicationupandrunning.