Java Script Lecturer Notes, Study notes of Javascript programming

Download Java Script Lecturer Notes and more Study notes Javascript programming in PDF only on Docsity!

JavaScript JavaScriptisthepremierclient-side interpretedscriptinglanguage.It‟swidelyusedin tasks rangingfrom thevalidationofform datatothecreationofcomplexuserinterfaces. DynamicHTMLisacombinationofthecontentformattedusingHTML,CSS,Scripting languageandDOM.Bycombiningallofthesetechnologies,wecancreateinteresting andinteractivewebsites.HistoryofJavaScript: NetscapeinitiallyintroducedthelanguageunderthenameLiveScriptinanearlybeta releaseofNavigator 2 .0in1 995 ,andthefocuswasonform validation.Afterthat,the languagewasrenamedJavaScript.AfterNetscapeintroducedJavaScriptinversion2. 0 oftheirbrowser,MicrosoftintroducedacloneofJavaScriptcalledJScriptinInternet Explorer 3. 0. WhataJavaScriptcando? JavaScriptgiveswebdevelopersaprogramminglanguageforuseinwebpages& allowsthem todothefollowing: JavaScriptgivesHTMLdesignersaprogrammingtool JavaScriptcanbeusedtovalidatedata JavaScriptcanreadandwriteHTMLelements Createpop-upwindows Perform mathematicalcalculationsondata Reacttoevents,suchasauserrollingoveranimageorclickingabutton Retrievethecurrentdateandtimefrom auser‟scomputerorthelasttimeadocument wasmodified Determinetheuser‟sscreensize,browserversion,orscreenresolution JavaScriptcanputdynamictextintoanHTMLpage JavaScriptcanbeusedtocreatecookies AdvantagesofJavaScript: Lessserverinteraction Immediatefeedbacktothevisitors Increasedinteractivity Richerinterfaces Websurfersdon‟tneedaspecialplug-intouseyourscripts JavaScriptisrelativelysecure. LimitationsofJavaScript: WecannottreatJavaScriptasafull-fledgedprogramminglanguage.Itlackssomeof theimportantfeatureslike: Client-sideJavaScriptdoesnotallowthereadingorwritingoffiles.Thishasbeen keptforsecurityreason. JavaScriptcannotbeusedfornetworkingapplicationsbecausethereisnosuch supportavailable. JavaScriptdoesn'thaveanymultithreadingormultiprocesscapabilities. Ifyourscriptdoesn‟tworkthenyourpageisuseless. Pointstoremember:  JavaScriptiscase-sensitive  Eachlineofcodeisterminatedbyasemicolon

 Variablesaredeclaredusingthekeywordvar  Scriptsrequireneitheramainfunctionnoranexitcondition.Therearemajor differencesbetweenscriptsand properprograms.Executionofascriptstarts withthefirstlineofcode&runsuntilthereisnomorecode JavaScriptcomments: InJavaScript,eachlineofcommentisprecededbytwoslashesandcontinuesfrom that pointtotheendoftheline. //thisisjavascriptcomment BlockcommentsorMultilinecomments:/**/ #JavaScriptisnotthesameasJava,whichisabiggerprogramminglanguage (althoughtherearesomesimilarities) JavaScriptandHTMLPage HavingwrittensomeJavaScript,weneedtoincludeitinanHTMLpage.Wecan‟t executethesescriptsfrom acommandline,astheinterpreterispartofthebrowser. Thescriptisincludedin thewebpageandrunbythebrowser,usuallyassoonasthe pagehasbeenloaded.Thebrowserisabletodebugthescriptandcandisplayerrors. EmbeddingJavaScriptinHTMLfile: Ifwearewritingsmallscripts,oronlyuseourscriptsinfewpages,thentheeasiestway istoincludethescriptintheHTMLcode.Thesyntaxisshownbelow: <scriptlanguage=”javascript”>

……

UsingExternalJavaScriptinHTMLfile: Ifweuselotofscripts,orourscriptsarecomplexthenincludingthecodeinsidethe webpagewillmakethesourcefiledifficulttoreadanddebug.Abetterideaistoputthe JavaScriptcodeinaseparatefileandincludethatcodeintheHTMLfile.Byconvention, JavaScriptprogramsarestoredinfileswiththe.jsextension. <scriptlanguage=”javascript”src=”sample.js”>

…… POPUPBOXESINJAVASCRIPT alert(“string”)opensboxcontainingthemessage confirm(“string”)displaysamessageboxwithOKandCANCELbuttons prompt(“string”)displaysapromptwindowwithfieldfortheusertoenteratext stringExample:

JavaScriptProgramming Elements

• Variables,datatypes,operators
• Statements
• Arrays
• Functions
• ObjectsinJavaScript
• ExceptionHandling
• Events
• DynamicHTMLwithJavaScript

VARIABLES

Like anyprogramming language,JavaScripthas variables.A variable is a name assignedtocomputermemorylocationtostoredata.Asthenamesuggests,thevalue ofthevariablecanvary,astheprogram runs.Wecancreateavariablewiththevar statement: var=; Example: varsum = 0 ;varstr; Wecaninitializeavariablelikethis: str=“hello”; Rulesforvariablenames: #Theymustbeginwithaletter,digitorunderscorecharacter#Wecan‟tusespaces innames#Variablenamesarecasesensitive#Wecan‟tusereservedwordasa variablename. WeaklyTypedLanguage: Mosthigh-levellanguages,includingCandJava,are stronglytyped.Thatis,avariable mustbedeclaredbeforeitisused,anditstypemustbeincludedinitsdeclaration.Once avariableisdeclared,itstypecannotbechanged. AstheJavaScriptis weaklytypedlanguage,datatypesarenotexplicitlydeclared. Example:varnum; num = 3 ; num ="SanDiego"; First,whenthevariable num isdeclared,itisempty.Itsdatatypeisactuallythetype undefined.Thenweassignittothenumber 3 ,soitsdatatypeisnumeric.Nextwe reassignittothestring"SanDiego",sothevariable‟stypeisnowstring. Example:

vars; s=“Hello”; alert( typeof s);s=5 4321 ; alert( typeofs);

DATATYPES

• JavaScriptsupportsfiveprimitivedatatypes:

numberstringbooleanundefinednull.

• Thesetypesarereferredtoas primitivetypesbecausetheyarethebasicbuilding blocksfrom whichmorecomplextypescanbebuilt.
• Ofthefive,onlynumber,string,andbooleanarerealdatatypesinthesenseofactually storingdata.
• Undefinedandnullaretypesthatariseunderspecialcircumstances.

NumericDataType: Thesearenumbersandcanbeintegers(suchas 2 , 2 2and2 000 )orfloating-point values(suchas 23. 42 ,- 56. 01 ,and2E 45 ). ValidwaystospecifynumbersinJavaScript

10177. 5 - 2. 71. 333333 e 77 - 1. 7 E 123 .E- 5128 e+ 100 Wecanrepresentintegersinoneofthefollowing3ways: Decimal:Theusualnumberswhicharehavingthebase 1 0arethedecimalnumbers Octal:Octalliteralsbeginwithaleadingzero,andtheyconsistofdigitsfrom zero throughseven.Thefollowingareallvalidoctalliterals: 000777024513600 HexaDecimal:Hexadecimalliteralsbeginwithaleading0x,andtheyconsistofdigitsfrom 0through9andlettersAthroughF.Thefollowingareallvalidhexadecimalliterals: 0 x 00 XF 8 f 000 x 1 a 3 C 5 e 7 Special Numeric Values: Specialvalue

Resultof Comparisions

Infinity,-Infinity Numbertoolargeortoo small torepresent

Allinfinityvaluescompare equaltoeachother

NaN UndefinedOperation NaNnevercomparesequalto anything,eventoitself

OperatorsinJavaScript TheoperatorsinJavaScriptcanbeclassifiedasfollows: Arithmeticoperators Relationaloperators Logicaloperators Assignmentoperators

Arithmeticoperators:

Note:Iftheargumentsof+arenumbersthentheyareaddedtogether.Ifthe argumentsarestringsthentheyareconcatenatedandresultisreturned. Example: