The Node Beginner Book.docx
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The Node Beginner Book.docx
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TheNodeBeginnerBook
About
TheaimofthisdocumentistogetyoustartedwithdevelopingapplicationswithNode.js,teachingyoueverythingyouneedtoknowabout"advanced"JavaScriptalongtheway.Itgoeswaybeyondyourtypical"HelloWorld"tutorial.
Status
Youarereadingthefinalversionofthisbook,i.e.,updatesareonlydonetocorrecterrorsortoreflectchangesinnewversionsofNode.js.ItwaslastupdatedonFebruary12,2012.
ThecodesamplesinthisbookaretestedtoworkwithNode.jsversion0.6.11.
Intendedaudience
Thisdocumentwillprobablyfitbestforreadersthathaveabackgroundsimilartomyown:
experiencedwithatleastoneobject-orientedlanguagelikeRuby,Python,PHPorJava,onlylittleexperiencewithJavaScript,andcompletelynewtoNode.js.
Aimingatdevelopersthatalreadyhaveexperiencewithotherprogramminglanguagesmeansthatthisdocumentwon'tcoverreallybasicstufflikedatatypes,variables,controlstructuresandthelikes.Youalreadyneedtoknowaboutthesetounderstandthisdocument.
However,becausefunctionsandobjectsinJavaScriptaredifferentfromtheircounterpartsinmostotherlanguages,thesewillbeexplainedinmoredetail.
Structureofthisdocument
Uponfinishingthisdocument,youwillhavecreatedacompletewebapplicationwhichallowstheusersofthisapplicationtoviewwebpagesanduploadfiles.
Which,ofcourse,isnotexactlyworld-changing,butwewillgosomeextramilesandnotonlycreatethecodethatis"justenough"tomaketheseusecasespossible,butcreateasimple,yetcompleteframeworktocleanlyseparatethedifferentaspectsofourapplication.YouwillseewhatImeaninaminute.
WewillstartwithlookingathowJavaScriptdevelopmentinNode.jsisdifferentfromJavaScriptdevelopmentinabrowser.
Next,wewillstaywiththegoodoldtraditionofwritinga"HelloWorld"application,whichisamostbasicNode.jsapplicationthat"does"something.
Then,wewilldiscusswhatkindof"real"applicationwewanttobuild,dissectthedifferentpartswhichneedtobeimplementedtoassemblethisapplication,andstartworkingoneachofthesepartsstep-by-step.
Aspromised,alongthewaywewilllearnaboutsomeofthemoreadvancedconceptsofJavaScript,howtomakeuseofthem,andlookatwhyitmakessensetousetheseconceptsinsteadofthoseweknowfromotherprogramminglanguages.
Thesourcecodeofthefinishedapplicationisavailablethrough theNodeBeginnerBookGithubrepository.
Tableofcontents
∙About
oStatus
oIntendedaudience
oStructureofthisdocument
∙JavaScriptandNode.js
oJavaScriptandYou
oAwordofwarning
oServer-sideJavaScript
o"HelloWorld"
∙AfullblownwebapplicationwithNode.js
oTheusecases
oTheapplicationstack
∙Buildingtheapplicationstack
oAbasicHTTPserver
oAnalyzingourHTTPserver
oPassingfunctionsaround
oHowfunctionpassingmakesourHTTPserverwork
oEvent-drivencallbacks
oHowourserverhandlesrequests
oFindingaplaceforourservermodule
oWhat'sneededto"route"requests?
oExecutioninthekingdomofverbs
oRoutingtorealrequesthandlers
oMakingtherequesthandlersrespond
▪Howtonotdoit
▪Blockingandnon-blocking
▪Respondingrequesthandlerswithnon-blockingoperations
oServingsomethinguseful
▪HandlingPOSTrequests
▪Handlingfileuploads
oConclusionandoutlook
JavaScriptandNode.js
JavaScriptandYou
Beforewetalkaboutallthetechnicalstuff,let'stakeamomentandtalkaboutyouandyourrelationshipwithJavaScript.Thischapterisheretoallowyoutoestimateifreadingthisdocumentanyfurthermakessenseforyou.
Ifyouarelikeme,youstartedwithHTML"development"longago,bywritingHTMLdocuments.YoucamealongthisfunnythingcalledJavaScript,butyouonlyuseditinaverybasicway,addinginteractivitytoyourwebpageseverynowandthen.
Whatyoureallywantedwas"therealthing",youwantedtoknowhowtobuildcomplexwebsites-youlearnedaprogramminglanguagelikePHP,Ruby,Java,andstartedwriting"backend"code.
Nevertheless,youkeptaneyeonJavaScript,yousawthatwiththeintroductionofjQuery,Prototypeandthelikes,thingsgotmoreadvancedinJavaScriptland,andthatthislanguagereallywasaboutmorethan window.open().
However,thiswasallstillfrontendstuff,andalthoughitwasnicetohavejQueryatyourdisposalwheneveryoufeltlikespicingupawebpage,attheendofthedayyouwere,atbest,aJavaScript user,butnotaJavaScript developer.
AndthencameNode.js.JavaScriptontheserver,howcoolisthat?
Youdecidedthatit'sabouttimetocheckouttheold,newJavaScript.Butwait,writingNode.jsapplicationsistheonething;understandingwhytheyneedtobewrittenthewaytheyarewrittenmeans-understandingJavaScript.Andthistimeforreal.
Hereistheproblem:
BecauseJavaScriptreallylivestwo,maybeeventhreelives(thefunnylittleDHMTLhelperfromthemid-90's,themoreseriousfrontendstufflikejQueryandthelikes,andnowserver-side),it'snotthateasytofindinformationthathelpsyoutolearnJavaScriptthe"right"way,inordertowriteNode.jsapplicationsinafashionthatmakesyoufeelyouarenotjustusingJavaScript,youareactuallydevelopingit.
Becausethat'sthecatch:
youalreadyareanexperienceddeveloper,youdon'twanttolearnanewtechniquebyjusthackingaroundandmis-usingit;youwanttobesurethatyouareapproachingitfromtherightangle.
Thereis,ofcourse,excellentdocumentationoutthere.Butdocumentationalonesometimesisn'tenough.Whatisneededisguidance.
Mygoalistoprovideaguideforyou.
Awordofwarning
TherearesomereallyexcellentJavaScriptpeopleoutthere.I'mnotoneofthem.
I'mreallyjusttheguyItalkedaboutinthepreviousparagraph.Iknowathingortwoaboutdevelopingbackendwebapplications,butI'mstillnewto"real"JavaScriptandstillnewtoNode.js.IlearnedsomeofthemoreadvancedaspectsofJavaScriptjustrecently.I'mnotexperienced.
Whichiswhythisisno"fromnovicetoexpert"book.It'smorelike"fromnovicetoadvancednovice".
IfIdon'tfail,thenthiswillbethekindofdocumentIwishIhadwhenstartingwithNode.js.
Server-sideJavaScript
ThefirstincarnationsofJavaScriptlivedinbrowsers.Butthisisjustthecontext.Itdefineswhatyoucandowiththelanguage,butitdoesn'tsaymuchaboutwhatthelanguageitselfcando.JavaScriptisa"complete"language:
youcanuseitinmanycontextsandachieveeverythingwithityoucanachievewithanyother"complete"language.
Node.jsreallyisjustanothercontext:
itallowsyoutorunJavaScriptcodeinthebackend,outsideabrowser.
InordertoexecutetheJavaScriptyouintendtoruninthebackend,itneedstobeinterpretedand,well,executed.ThisiswhatNode.jsdoes,bymakinguseofGoogle'sV8VM,thesameruntimeenvironmentforJavaScriptthatGoogleChromeuses.
Plus,Node.jsshipswithalotofusefulmodules,soyoudon'thavetowriteeverythingfromscratch,likeforexamplesomethingthatoutputsastringontheconsole.
Thus,Node.jsisreallytwothings:
aruntimeenvironmentandalibrary.
Inordertomakeuseofthese,youneedtoinstallNode.js.Insteadofrepeatingtheprocesshere,Ikindlyaskyoutovisit theofficialinstallationinstructions.Pleasecomebackonceyouareupandrunning.
"HelloWorld"
Ok,let'sjustjumpinthecoldwaterandwriteourfirstNode.jsapplication:
"HelloWorld".
Openyourfavoriteeditorandcreateafilecalled helloworld.js.Wewantittowrite"HelloWorld"toSTDOUT,andhereisthecodeneededtodothat:
console.log("HelloWorld");
Savethefile,andexecuteitthroughNode.js:
nodehelloworld.js
Thisshouldoutput HelloWorld onyourterminal.
Ok,thisstuffisboring,right?
Let'swritesomerealstuff.
AfullblownwebapplicationwithNode.js
Theusecases
Let'skeepitsimple,butrealistic:
∙Theusershouldbeabletouseourapplicationwithawebbrowser
∙Theusershouldseeawelcomepagewhenrequestinghttp:
//domain/startwhichdisplaysafileuploadform
∙Bychoosinganimagefiletouploadandsubmittingtheform,thisimageshouldthenbeuploadedtohttp:
//domain/upload,whereitisdisplayedoncetheuploadisfinished
Fairenough.Now,youcouldachievethisgoalbygooglingandhackingtogethersomething.Butthat'snotwhatwewanttodohere.
Furthermore,wedon'twanttowriteonlythemostbasiccodetoachievethegoal,howeverelegantandcorrectthiscodemightbe.WewillintentionallyaddmoreabstractionthannecessaryinordertogetafeelingforbuildingmorecomplexNode.jsapplications.
Theapplicationstack
Let'sdissectourapplication.Whichpartsneedtobeimplementedinordertofulfilltheusecases?
∙Wewanttoservewebpages,thereforeweneedan HTTPserver
∙Ourserverwillneedtoanswerdifferentlytorequests,dependingonwhichURLtherequestwasaskingfor,thusweneedsomekindof router inordertomaprequeststorequesthandlers
∙Tofulfilltherequeststhatarrivedattheserverandhavebeenroutedusingtherouter,weneedactual requesthandlers
∙TherouterprobablyshouldalsotreatanyincomingPOSTdataandgiveittotherequesthandlersinaconvenientform,thusweneed requestdatahandling
∙WenotonlywanttohandlerequestsforURLs,wealsowanttodisplaycontentwhentheseURLsarerequested,whichmeansweneedsomekindof viewlogic therequesthandlerscanuseinordertosendcontenttotheuser'sbrowser
∙Lastbutnotleast,theuserwillbeabletouploadimages,sowearegoingtoneedsomekindof uploadhandling whichtakescareofthedetails
Let'sthinkamomentabouthowwewouldbuildthi
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