Bioinformacs Resources - Rostlab · 2017-06-30 · Immutability & wrapping object Strings are a primi)ve immutable type ... JS Object is an associave array (think python dic)onary),

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Bioinforma)csResources

Lecture&ExercisesProf.B.Rost,Dr.L.Richter,J.Reeb

Ins)tutfürInforma)kI12

SlidesbyD.Nechaev

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Origins

●  BrendanEich,Netscape,1995

●  LanguagefortheNetscapeNavigatorbrowser

●  CalledJavaScriptbecausemarke)ng

●  InspiredbyScheme(func)onallanguage)andSelf(prototypes),notbyJava

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JScript

●  MicrosoQreverseengineeredJavaScript

●  CalleditJScriptandaddedtotheInternetExplorerin1996

●  JScript&JavaScripthadincompa)bili)es,browserwarstarted

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ECMAScript

●  ECMAScript–standardizedspecifica)on,1997

●  latestedi)on(ECMAScript6)finalizedinJune2015

●  ES6iss)llnotcompletelysupportedbythebrowsers

●  ThistalkpresentsES5features

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LanguagefortheBrowser

●  Designedasabrowserlanguagewithnoinput/outputcapabili)es

●  Interac)onwiththeenvironment(HTMLpage)●  use`script`tagtoaddjsfilestothepage

<script src="filename" type="text/javascript"></script>

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Node.js

●  Pla^ormforrunningJavaScriptontheserverside(2009)

●  U)lizesGoogle’sV8JavaScriptenginetointerpretJavaScriptcode

●  AllowstowritebothbackendandfrontendcodeinJavaScript

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JavaScript

●  Complexapplica)onsstartedbeingdevelopedinthesecondhalfof2000sasWeb2.0emerged

●  Currentlyisoneofthemostpopularlanguages

●  AllowstocreaterichUserInterfacesfortheWeb(plots,diagrams,classicalUIelements,etc.)

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SimpleExecu)onEnvironment

●  OneofthesimplestwaystorunJavaScriptcodeistouseChromeGoogleDeveloperTools

●  Cmd+Alt+IorCtrl+Alt+I

●  Alterna)vely,rightclick,choose`Inspect`,select`Console`tab

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Firstlookatvariables

●  `var`keywordallowstodeclareandini)alizevariables(severalatonce)

●  valididen)fiersbeginwithaleger,`$`,or`_`●  othersymbolscanbelegers,digits,`$`,and`_`

< var identifier; < var factory, $obj, _private; < var meaning = 42, level = 9000;

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DataTypes

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DataTypes

●  Primi)ve:-  Number-  String-  Boolean-  null-  undefined

●  Referenced:-  Object-  Array-  Date-  Regexp-  Func)on

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Number,0.1+0.2

●  Onlyonetypefornumbers-float●  uses8bytesfornumberrepresenta)on

●  becarefulwithfinancialdata

< 0.1 + 0.2 === 0.3; > false < 0.1 + 0.2; > 0.30000000000000004

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Math.pow

●  Standardarithme)calopera)onsandmoduloaredefinedfornumbers

●  `Math`objectimplementsmorecomplexmathopera)ons

< 10 % 3; > 1 < Math.pow(2, 10); > 1024

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Numberliterals

●  Numberswrigeninthesourcecode(asintheexamplesabove),decimalbydefault,hexadecimalbeginwith`0x`

●  Floatliteralscontain`.`or`e`

●  prefixoperator`-`isusedfornega)venumbers

< 0xF; > 15 < 101e-1; > 10.1 < -10; > -10

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SpecialValues

●  `Infinity`&`-Infinity`arereturnedinthecaseofoverflow

●  NaNisreturnedfortheopera)onswithnodefinedvalue

< -1e1000; > -Infinity < 1 / 0; > NaN

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Wrappingobject

●  Numbersareaprimi)vetype(byvalue)●  `Number`constructorallowstocreatewrappingobjects

< typeof 7; > "number" < typeof new Number(7); > "object" < (new Number(7)).valueOf(); > 7

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Strings

●  Stringisasequenceof16-bitUnicodesymbols●  Nochartype

●  Stringliteralbeginsandendswith`'`or`"`(nodifference)

< 'Rostlab\t\n' === "Rostlab\t\n"; > true

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ComplexStrings

●  Nointerpola)on,concatenate●  Breakstringsintomul)plelineswith`\`

< 'Rostlab ' + 2016; > "Rostlab 2016” < 'a\ < b'; > "ab"

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Immutability&wrappingobject

●  Stringsareaprimi)veimmutabletype

●  Methodslike`replace()`and`toLowerCase()`returnanewstring

●  `String`constructorallowstocreatewrappingobjects

< typeof new String("Rostlab"); > "object” < (new String("Rostlab")).valueOf(); > "Rostlab"

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Boolean

●  Booleantypehastwovalues-`true`and`false●  Anyexpressionusedinacondi)onalisautoma)callyconvertedtoBoolean

●  `null`,`undefined`,0,`NaN`,and`“”`=>`false`

●  anythingelse=>`true`

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Wrappingobject

●  `Boolean`constructorallowstocreatewrappingobjects

●  Becareful–wrappingobjectfor`false`isevaluatedastrue!

< if (new Boolean(false)) { console.log("is true"); } > is true

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undefined

●  Specialtypeundefinedhasonlyonevalue–`undefined`

●  unini)alizedvariable,nonexistentarrayelementorobjectproperty

●  returnedbyfunc)onswithnoexplicitreturnvalue

●  func)onparameterwithnocorrespondingargument

< var x; < x > undefined

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undefined

●  globalvariable`undefined`returnsvalue`undefined`,whichistheonlyvalueoftype`undefined`

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null

●  Abitcomplicated

●  `null`isakeyword

●  `typeof`returns`object`

●  However,`null`hasnoproper)esandnomethodsunlikeotherobjects

●  nullisasingleinstanceofaspecialtypemeaningnovalue< typeof null; > "object"

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null

●  Justafewofinbuiltfunc)onsreturnnull●  Thus,itisconsideredagoodprac)cetouse`null insteadof`undefined`inusercodetoindicateabsenceofvalue

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Objects

●  JSObjectisanassocia)vearray(thinkpythondic)onary),i.e.asetofproper)es,whereeachpropertyisakey-valuepair

●  Objectsarestoredbyreference

< var a = { name: 'Rostlab’ }, b = a; < b.name = 'Rostlab 2016'; < a.name; > "Rostlab 2016"

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ObjectContents

●  Noclasses,sonolimitsonthenamesandvaluesoftheproper)es

●  Anobjectcanhavearbitraryproper)es

●  Anobject’sproperty’svaluecanbeanotherobject

●  Toaccessanobject’spropertyusedotnota)onorsquarebracketnota)on

< var lct = { name: 'Dr. Richter' }; < var cls = { name: 'BioinfRes', lecturer: lct }; < cls.lecturer.name; > "Dr. Richter” < cls['lecturer'].name; > "Dr. Richter” < cls.lecturer['name']; > "Dr. Richter"

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Noclasses?

●  Yes,noclasses●  Prototypalinheritanceisusedforcodereuseandmodelinggroupsofobjectswithsimilarbehavior

●  Arrays,func)ons,regularexpressions,anddatesareobjectsandtheygettheirbehaviorviaprototypalinheritance

●  We’lllookatitindetailslater

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Array

●  Anobjectthatstoresanorderedgroupofvalues●  Dynamic(canchangesize)anduntyped(canstorevaluesofdifferenttypes)

●  othersymbolscanbelegers,digits,`$`,and`_`

< var array = ['Rostlab']; < array.push(2016); < array; > ["Rostlab", 2016]

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Anyvalue

●  Anarraycanholdanyvalueincludingitself

=^__^=< var array = ['Rostlab']; < array.push(array); < array[1][0]; > "Rostlab"

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Date

●  Objectscreatedwiththe`Date`constructorhavemethodsforhandlingdatesand)me

< var now = new Date(); < now.getFullYear(); > 2016

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Regexps

●  Regexpobjectsdescribethestringtemplate

< var regexp = new RegExp('^Rostlab'); < regexp.test('Rostlab 2016'); > true; < regexp.test('2016 Rostlab'); > false

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Func)ons

●  Func)onsaresocalled‘firstclassci)zens’:

-  canstoreinvariables,arrays,objects’proper)es

-  canpasstootherfunc)onsasarguments

-  canreturnfromotherfunc)ons

●  Func)onsaremul)ary(don’tknowwhat`mul)ary`means?Comparewith`unary`,`binary`,etc.;-)

●  Ifwedon’tpassanargumentforacertainparameter,itsvalueis`undefined`

●  Canaccessallargumentspassedtoafunc)onwiththe`arguments`keyword

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Func)ons

●  Graspingfunc)onsisessen)alforJavaScript●  We’lllookatfunc)onsindetail< function printArgs(a, b, c) { console.log(a); console.log(b); console.log(c); }; < printArgs('Rostlab', 2016); > Rostlab > 2016 > undefined

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Summary

●  `Boolean`,`Number`,and`String`areprimi)veimmutableobjectsstoredbyvalue

●  Wecancreatewrapperobjectsforprimi)vevalues

●  That’sexactlywhathappenswhenwecallamethodonaprimi)vevalue–awrapperobjectiscreated,amethodiscalledonthewrapperobject,thenthewrapperobjectisdestroyed

< (2016).toString(); > "2016” < ' Rostlab '.trim(); > "Rostlab"

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SummaryPt.2

●  `null`&`undefined`aretheonlyvaluesoftheirrespec)vedatatypes

●  Nowrapperobjectsforthem

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SummaryPt.3

●  Objectsarestoredbyreference●  Objectsaremutable

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Typeconversions

●  Func)ons`Number`,`Boolean`,and`String`●  Func)ons`parseFloat`and`parseInt`

●  Methods`toString`,`toExponen)al`,`toFixed`,and`toPrecision`

< String(2016); > "2016” < Boolean(2016); > true < (123.45).toExponential(); > "1.2345e+2"

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Strongtyping

●  Somelanguages(e.g.,Python)havestrongtyping●  Strongtypingmeanswecan’tmixvaluesofdifferenttypes

>>> 'Rostlab ' + 2016Traceback (most recent call last): File "<stdin>", line 1, in <module>TypeError: cannot concatenate 'str' and 'int' objects

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Weaktyping

●  JavaScriptisadynamicweaklytypedlanguage●  JavaScriptdoesn’tcare!

< 'Rostlab ' + 2016; > "Rostlab 2016"

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Weaktyping

● REALLYdoesn’tcare< '7' * '4'; > 28

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Weaktyping

●  Please,beverycareful

●  Rulesofautoma)ctypecas)ngarecomplex

< '6' - '4'; > 2 < '6' + '4'; > "64"

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Doubleequalityoperator

●  Doubleequalityoperatorautoma)callydoestypeconversion

●  Thatmakesitintransi)ve

< '0' == 0 && 0 == ''; > true < '0' == ''; > false

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Tripleequalityoperator

●  Tripleequalityoperatorreturns`true`onlyifoperandsbelongtothesamedatatypeandholdthesamevalue

●  Itisconsideredagoodprac)cetouse`===`and`!==`operatorsinsteadofdoubleequality

< '0' === 0; > false < 0 === ''; > false

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Magicstrings

●  Automa)ctypecas)ngisdangerousbutallowstoperformsomefuntricks

< ![]; > false < !![]; > true < +!![]; > 1

< !![] + []; > "true” < (!![]+[])[+![]]; > "t”

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Magicstrings

●  Automa)ctypecas)ngisdangerousbutallowstoperformsomefuntricks

< +!![]+(+!![])+[]+(+![])+(+!![])+(+!![]+(+!![]))*(+!![]+(+!![])+(+!![]))+([]+{})[+!+[]+!+[]+!+[]+!+[]+!+[]+!+[]+!+[]]+([]+!![])[+!+[]]+([]+{})[+!+[]]+([]+![])[+!+[]+!+[]+!+[]]+([]+{})[+!+[]+!+[]+!+[]+!+[]+!+[]+!+[]]+([]+![])[+!+[]+!+[]]+([]+![])[+!+[]]+([]+{})[+!+[]+!+[]];> "2016 rostlab"

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ControlStatements

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ControlStatements

●  `if–else`,`switch`andternaryoperator●  `while`and`for`loop

●  `break`and`con)nue`instruc)ons

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Ifelse

●  Canuse`if`againaQer`else`

●  Usecurlybracesifwanttoexecutemorethanonestatement

●  Itisconsideredagoodprac)cetoalwaysusecurlybraces

< if (hand === 'Rock') { console.log('Rock beats scissors, you win'); } else if (hand === 'Paper') { console.log('Scissors beat paper, you lose'); } else { console.log('Try again'); }

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Ternaryoperator

●  Ternaryoperatorallowstowritecondi)onalinamorecompactway

●  `if–else`condi)onal:ifcondi+ondo1elsedo2

●  Ternaryoperator:condi)on?do1:do2

< console.log(grade > 4 ? 'Fail' : 'Pass’)

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Ternaryoperator

●  Wecanuseternaryoperatorinsideanotherternaryoperator

●  Justbecausewecandoesn’tmeanweshould

●  Whatisthefollowingcodedoing?

< return (a<b) ? (b<c) ? b : (a<c) ? c : a : (a<c) ? a : (b<c) ? c : b;

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Ternaryoperator

●  Thefollowingcodereturnsmedianofa,b,andc●  Unreadableandunmaintainable

< return (a<b) ? (b<c) ? b : (a<c) ? c : a : (a<c) ? a : (b<c) ? c : b;

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Switch

●  `switch`allowstochooseoneofmanystatements

●  Wecandothesamewithmul)pleif–else,but`switch`allowstowritemorecompactandreadablecode

< switch(month) { case 0: 'Jan'; break; case 1: 'Feb'; break; …

case 11: 'Dec'; break; default: 'Unknown'; break; }

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Switch●  `switch`comparesvalueofthecondi)onalwiththevalueofeach`case`un)l

`===`operatorreturnstrue

●  Onceequalityisfound,respec)vecodeblockisexecuted

●  Unlesswe`break`outof`switch`statement,allofthebelowcodeblockswillbeexecutedaswell

●  `default`codeblockisexecutedifnoequalityisfound< switch(month) { case 0: 'Jan'; break; case 1: 'Feb'; break; …

case 11: 'Dec'; break; default: 'Unknown'; break; }

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Forloop

●  JavaScript`for`loopisanalogoustoC`for`loop●  for(init;condi)on;post-itera)on-statement)loop-statement

< for (var i = 0; i < 10; i++) console.log(i); > 0 > 1 > … > 9

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Cthulhuloop

●  Wecaneasilycreateaninfiniteloop(;;)

●  Butjustbecausewecandoesn’tmeanweshould

< for (;;) //in the name of Cthulhu console.log('All your CPU are belong to Cthulhu!');

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For–inloop

●  `for-in`loopiteratesoverobjectproper)es’names

●  Togetproperty’svalueusesquarebracketnota)on

< var cls = {name: 'Rostlab', year: '2016', lecturer: 'Dr. Richter'}; < for (var p in cls) { console.log(p + ': ' + cls[p]); }; > name: Rostlab > year: 2016 > lecturer: Dr. Richter

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While

●  `while`loopexecutesablockcodewhilethecondi)onistrue

●  while(condi)on)statement

< var i = 0; < while (i < 10) { console.log(i); i++; }

> 0 > 1 > … > 9

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Dowhile

●  `do–while`loopexecutesablockcode,thenchecksthecondi)onandstartsanotheritera)onifitistrue

●  Willrunatleastonce

< var i = 11; < do { console.log(i); i++; } while (i < 10); > 11

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Break,con)nue,label

●  `break`abortscurrentloopand`switch`statement

●  `con)nue`startsnextloopitera)on

●  Wecanuselabelswith`break`and`con)nue`

●  LabelslooksuspicioslysimilartoGOTO

●  Researchanduseatyourownrisk< outerLoop: while (true) { innerLoop: while(true) { console.log('No more loops'); break outerLoop; }; console.log('You won\'t see me!'); } > No more loops

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Logicaloperators

●  Wecanuselogicaloperatorsincomplexcondi)ons

●  Use`&&`for`AND`,`||`for`OR`,and`!`for`NOT`

< true && false; > false < true || false; > true < !false; > true

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Changingpriorityofopera)ons

●  Useparenthesistochangepriorityofopera)ons

< 2 + 2 * 2 > 6 < (2 + 2) * 2 > 8

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Func)ons

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Func)onDeclara)on

●  Usekeyword`func)on`followedbyafunc)on’snameandalistofparameters

< function functionName(par1, ..., parN) { statements }

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Func)onExpression

●  Allowstocreateanonymousfunc)ons●  Wecanassigncreatedfunc)ontoavariable

< var varName = function(par1, ..., parN) { statements }

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Func)onExpressionwithaName

●  Wecanevenuseafunc)onexpressionwithaname

●  Insuchcasewewillonlybeabletocallafunc)onbyit’snameinsidethefunc)onitself

< var myFactorial = function factorial(n) { if (n > 0) { return n * factorial(n - 1); } else { return 1; } }; < factorial(3); > Uncaught ReferenceError: factorial is not defined(…) < myFactorial(3); > 6

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Declara)onandExpression

●  Bothdefinefunc)ons

●  Func)ondeclara)onrequiresaname,whilefunc)onexpressionallowsanonymousfunc)ons

●  Thankstofunc)ondeclara)onhois)ngwecanusefunc)onsbeforetheyaredeclared,asiffunc)ondeclara)onwasliQedtothetopoftheblock

●  Finally,wecan’tdeclarefunc)onsinsideloops,condi)onalsandothercontrolstatements,whilefunc)onexpressionshavenosuchlimits

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Func)onDeclara)onHois)ng

< factorial(5); function factorial(n) { result = 1; for (var i = 1; i <= n; i++) { result *= i; } return result; } > 120

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WorkingwithArguments

●  Func)onhasparametersandtakesarguments

●  Wecaninvokeafunc)onwithadifferentamountofargumentsthanparameters

●  Parameterswithnocorrespondingargumentwillhavevalue`undefined`

< function myFunc(str1, str2) { console.log(str2); }; myFunc('only one argument!') > undefined

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WorkingwithArguments

●  Ifthenumberofargumentsislargerthanthenumberofparameters,“excessive”argumentssimplywillnotbeused

●  Wes)llcanaccessthemthankstoaspecialvariable`arguments`

●  `arguments`objectcontainsalltheargumentspassedtoafunc)on

< function myFunc(str1, str2) { console.log(arguments[3]); }; myFunc('one', 'two', 'three', 'four'); > four

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Workingwith`arguments`object

●  Although`arguments`objecthas`length`propertyandallowstoaccessitselementsbyindex,itisnotanarrayanddoesnothavearraymethods

< ['one', 'two', 'three', 'four'].indexOf('three'); > 2 < function myFunc(str1) { return arguments.indexOf('three'); } myFunc('one', 'two', 'three', 'four'); > TypeError: arguments.indexOf is not a function

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Workingwith`arguments`object

●  S)ll,wecanconvert`arguments`objecttoanarrayusing`Array.prototype.slice.call(arguments)`

●  We’llinves)gatethiscodeindetailsaliglebitlater,fornowtreatitasasnippet

< ['one', 'two', 'three', 'four'].indexOf('three'); > 2 < function myFunc(str1) { var argumentsArray = Array.prototype.slice.call(arguments); return argumentsArray.indexOf('three'); } myFunc('one', 'two', 'three', 'four'); > 2

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Func)onReturnValue

●  Func)onalwaysreturnsavalue●  Bydefault`undefined`isreturned

●  Toreturnadifferentvalueuse`return`keyword

< function square(a) { return Math.pow(a, 2); } square(7); > 49

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Automa)cSemicolonInser)on

●  RememberaboutASIandputthereturnedvalueonthesamelineas`return`keyword

< function f1() { return { year: 2016 } } < func1() > undefined

< function f2() { return { year: 2016 } } < f2() > Object {year: 2016}

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Automa)cSemicolonInser)on

●  ThankstotheAutoma)cSemicolonInser)oncodeontheleQisequaltocodeontheright

< function f1() { return { year: 2016 } }

< function f1() { return; //ßALARM { year: 2016 } }

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NoBlockScopinginJavaScript

●  Insomeotherlanguages,declaringavariableinsideablockcreatesavariableonlyinsidethatblock

●  InJavaScriptavariablewillbevisibleoutsidethisblockaswell

< for (var i = 0; i < 3; i++) { console.log(i); }; > 0 1 2 < i > 3 // if you wonder, why it’s 3, study loops again

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Func)onsCreateScope

●  Func)onsaretheonlywaytocontrolscope●  Eachfunc)oncreatesanewscope

●  Avariabledeclaredinascopeisaccessibleinsidealloftheinnerscopes

< var name = 'Rostlab'; function printName() { console.log(name); } printName(); > Rostlab

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InnerFunc)onsandOuterScope

●  Let’ssayitinadifferentway–wecanaccessinsideafunc)onallofthevariablesdeclaredinthisfunc)on’souterscope

●  Wecanbothreadandwritesuchvariables

< var name = 'Rostlab'; function rebranding() { name = 'Bioinformatics Chair'; } rebranding(); name > "Bioinformatics Chair"

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Variableshadowing

●  Declaringavariablewiththesamenameasavariableinanouterscopeblocksaccesstotheoutervariable

< var name = 'Rostlab'; function rebranding() { var name = 'Bioinformatics Chair'; } rebranding(); name > "Rostlab"

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Variablehois)ng

●  Variabledeclara)onsarehoistedaswellasfunc)ondeclara)ons

●  Avariabledeclara)onis‘liQed’tothetopofitsscope

< var name = 'Rostlab'; function rebranding() { name = 'Bioinformatics Chair'; var name; } rebranding(); name > "Rostlab"

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IIFE

●  ImmediatelyInvokedFunc)onExpressionsallowustopreventloitering

●  VariablesdeclaredinsideIIFEareinaccessibleoutside

< (function() { var iDoNotPolluteOuterScope; }()); iDoNotPolluteOuterScope > Uncaught ReferenceError: iDoNotPolluteOuterScope is not defined

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Higherorderfunc)ons

●  Ahigherorderfunc)ontakesafunc)onasanargumentorreturnsafunc)onasareturnvalue

< function add(x) { return function innerAdd(y) { return x + y; } } add(4)(5) > 9

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add(4)(5)

●  `add(x)`takesanintegerasanargumentandreturnsanotherfunc)onthattakesanotherintegerasanargument

●  `add(4)`returns`innerAdd(y)`andweimmediatelycallitpassing5asanargument

< function add(x) { return function innerAdd(y) { return x + y; } } add(4)(5) > 9

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Closures

●  Howcan`innerAdd`func)onaccessvariable`x`aQer`add`func)onhasbeeninvoked?

●  It’sallabouttheclosures●  JavaScriptinnerfunc)onhasanaccesstooutervariablesevenwhenanouterfunc)onhasbeenrun

●  Afunc)on“encloses”itsenvironment

●  Aclosureisfunc)onplusitscontext

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Classicexample–asimplecounter

●  IIFE+closure< var counter = (function() { var cntr = 0; return function() { return ++cntr; } }()); counter(); > 1 < counter(); > 2 < counter(); > 3

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Objects

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Objects–Recap

●  Anobjectisanassocia)vearray,i.e.asetofproper)es,ofpairs`name-value`

●  Anobjectismutableandispassedbyreference,itcanhavearbitraryproper)eswhosevaluescanbeofanytype,includingfunc)onsandotherobjects

●  Arrays,func)ons,regularexpressionsanddatesareobjectsaswell

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Crea)nganObject

●  `newObject()`createsanewobjectwithnoproper)es

●  Havingcreatedanobject,wecanaddproper)esonebyone

< var cls = new Object(); cls.name = 'Bioinformatics Resources'; cls.year = 2016; cls > Object {name: "Bioinformatics Resources", year: 2016}

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Objectliteral

●  Anobjectliteralallowstocreateanobjectwithitsproper)esfilled

●  Anobjectliteralisalistofproper)es(name-valuepairs)incurlybraces

< var cls = { name: 'Bioinformatics Resources', year: 2016, } cls > Object {name: "Bioinformatics Resources", year: 2016}

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Propertynames

●  WecanusevalidJSiden)fiersaspropertynamesandaccesssuchproper)esviadotnota)on

●  Avalididen)fierstartswithaleger,anunderscore(_),oradollarsign($)

●  Subsequentcharacterscanbelegers,digits,underscores,ordollarsigns

< var validNames = { valid: 'valid name', $_$: 'valid as well', _$_100500: 'this is valid too', }; validNames._$_100500 > "this is valid too"

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Propertynames

●  Wecanusestringsthatarenotvalididen)fiersaswell

●  Wehavetoquotethemandaccessviasquarebracketnota)on

< var validNames = { '100500': 'this is valid', }; validNames['100500'] > "this is valid"

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Propertyvalues

●  Apropertyvaluecanbeofanytype

●  Func)onsthatareproper)esofanobjectarecalled‘methods’

●  Insideofamethod`this`keywordreferstotheobjectthemethodiscalledon

●  Wecanuseanystringasaproperty’sname

●  Quoteaproperty’snameifit’snotavalididen)fier

< var cls = { name: 'Bioinformatics Resources', year: 2016, print: function() { console.log(this.name + ', ' + this.year); } } cls.print() > Bioinformatics Resources, 2016

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Workingwithproper)es

●  Wecanread,write,add,anddeleteproper)es

< var cls = { name: 'Bioinformatics Resources', year: 2016, } cls.chair = 'Rostlab'; console.log(cls); > Object {name: "Bioinformatics Resources", year: 2016, chair: "Rostlab"} < delete cls.chair; console.log(cls) > Object {name: "Bioinformatics Resources", year: 2016} < cls.chair > undefined

BioinfRes SoSe17

Itera)ngoverproper)es

●  `for-in`loopiteratesoverobjectproper)es’names

●  Togetproperty’svalueusesquarebracketnota)on

< var cls = { name: 'Bioinformatics Resources', year: 2016, print: function() { console.log(this.name + ', ' + this.year); } } for (var p in cls) { console.log(p + ': ' + cls[p]); }; > name: Bioinformatics Resources year: 2016 print: function () { console.log(this.name + ', ' + this.year); }

BioinfRes SoSe17

Checkingpropertyexistence

●  `hasOwnProperty()`methodallowsustocheckifanobjecthasagivenproperty

< cls.hasOwnProperty('year') > true < cls.hasOwnProperty('month') > false

BioinfRes SoSe17

Comparingobjects

●  Anobjectisequalonlytoitself●  Inotherwords,equalityoperatorreturns`true`onlyifbothvariablesholdareferencetothesameobject

< lecture = cls; lecture === cls; > true < {name: 'value'} === {name: 'value'} > false

BioinfRes SoSe17

Prototypes

●  Bytheway,weneveradded`hasOwnProperty`methodtoourobjects,butwes)llwereabletouseit.Why?

●  Becauseprototypes!

< ({}).hasOwnProperty('year'); > false

BioinfRes SoSe17

PrototypalInheritance

●  Eachobjecthasaspecialconnec)ontoanotherobject,toaprototype.Whenwetrytoaccessapropertythatisabsentinanobject,weaccessapropertyoftheprototype.Wecansaythatobjectinheritsitsprototypeproper)es.

●  `Object.prototype`isaprototypeofallobjectscreatedviaanobjectliteral.`Object.prototype`has`hasOwnProperty`method,andthat’sexactlywhatweinvoked.

BioinfRes SoSe17

PrototypalInheritance

●  Ifweaddapropertytoaprototype,alloftheobjectsinheri)ngfromthisprototypewillgetimmediateaccesstothenewproperty

< Object.prototype.easterEgg = 'Hello, world!'; cls.easterEgg > "Hello, world!"

BioinfRes SoSe17

PrototypalInheritance

●  Whathappensifweadd`easterEgg`propertytoour`cls`object?

< cls.easterEgg = function() { console.log('Have I messed up my prototype?'); } cls.easterEgg(); > Have I messed up my prototype? < Object.prototype.easterEgg; > "Hello, world!” < ({}).easterEgg; > "Hello, world!"

BioinfRes SoSe17

Func)onsRevisited

BioinfRes SoSe17

Func)onsareObjects

●  Afunc)onisanobject

●  `name`property’svalueisfunc)on’sname(anemptystringforananonymousfunc)on)

●  `length`property’svalueisanamountofparameters

< (function() {}).name > "" < var foo = function bar(a, b, c) {}; foo.name; > "bar” < foo.length; 3

BioinfRes SoSe17

Func)on.prototype

●  Func)onobjectisconnectedtoaprototypeaswell

●  `Func)on.prototype`istheprototypeoffunc)ons

< Object.getPrototypeOf(foo) === Function.prototype > true

BioinfRes SoSe17

`apply`&`call

●  Func)onsinherit`apply`and`call`methods< var print = function() { console.log(this.name + ', ' + this.year); }; var cls = { name: 'Bioinformatics Resources', year: 2016, } print.apply(cls); > Bioinformatics Resources, 2016 < print.call(cls); > Bioinformatics Resources, 2016

BioinfRes SoSe17

`apply`&`call

●  `apply`&`call`methodsallowtocallafunc)onasifitwasamethodoftheobjectthatispassedasafirstargument

●  `this`keywordreturnspassedobject

< var returnThis = function() { return this; } returnThis.apply(cls) === cls; > true

BioinfRes SoSe17

`apply`&`call

●  ArgumentspassedaQertheobjectbecomeargumentsofthefunc)on

●  `call`takestheseargumentssimplyasarguments,`apply`takesanarray

< var print = function(times) { for (var i = 0; i < times; i++) { console.log(this.name); } }; print.call(cls, 3); > Bioinformatics Resources Bioinformatics Resources Bioinformatics Resources

BioinfRes SoSe17

Arrayasargumentswith`apply

●  Using`apply`wecanunpackarguments,thatis,turnanarrayintoargumentsforafunc)on

●  Amnemonicallowstorememberwhichoftwomethodstakesanarray:“apply”and“array”startandendwiththesamelegers

< Math.max(3, 5, 9); > 9 < Math.max([3, 5, 9]); > NaN < Math.max.apply(null, [3, 5, 9]); > 9

BioinfRes SoSe17

ArgumentsArray

●  Previouslyshownwayofturning`arguments`objectintoanactualarrayshouldbeclearnow

< Array.prototype.slice.call(arguments);

BioinfRes SoSe17

CallingOneObject’sMethodsonAnotherObject

●  Wecaninvokeoneobject’smethodsonanotherobjectusing`apply`and`call`orsimplybyaddingmethodstoanotherobject

< var cls = { name: 'Bioinformatics Resources', year: 2016, print: function() { console.log(this.name + ', ' + this.year); } }; var anotherCls = { name: 'Protein Prediction', year: 2016, }; anotherCls.print = cls.print; anotherCls.print(); > Protein Prediction, 2016

BioinfRes SoSe17

LateBinding

●  `this`becomesboundtoanobjectattheinvoca)on)me

●  Latebindingallowstouse`apply`&`call`orcopymethodsfromoneobjecttoanother

●  Unless…

BioinfRes SoSe17

Func)on.prototype.bind

●  `Func)on.prototype.bind`returnsanewfunc)onboundtoaspecifiedobject

●  `this`keywordwillalwaysreturnboundobject< var cls = { name: 'Bioinformatics Resources', year: 2016, }; cls.print = (function() { console.log(this.name + ', ' + this.year); }).bind(cls); var anotherCls = { name: 'Protein Prediction', year: 2016, }; anotherCls.print = cls.print; anotherCls.print(); > Bioinformatics Resources, 2016

BioinfRes SoSe17

`this

●  Whatwill`this`returnifafunc)onhasn’tbeenboundtoanobjectandisnotinvokedasamethodorvia`apply`or`call`?

●  Bydefault`this`returnstheglobalobject

●  Inthebrowserit’s`window`object

< function checkThisOut() { console.log(this); }; checkThisOut(); > Window {external: Object, chrome: Object, document: document, GoogleAnalyticsObject: "ga", gaplugins: Object…}

BioinfRes SoSe17

`this

●  Inaninnerfunc)on`this`bydefaultreturnstheglobalobject

< var cls = { name: 'Bioinformatics Resources', testInnerFunc: function() { return (function() { console.log(this); }()); } }; cls.testInnerFunc(); > Window {external: Object, chrome: Object, document: document, GoogleAnalyticsObject: "ga", gaplugins: Object…}

BioinfRes SoSe17

`this`andthat

●  However,wealreadyknowhowtodealwithit●  Wecaneitherbindaninnerfunc)onorcache`this`inanothervariable,forexample`that`

< var cls = { name: 'Bioinformatics Resources', testInnerFunc: function() { var that = this; return (function() { console.log(that); }()); } }; cls.testInnerFunc(); > Object {name: "Bioinformatics Resources"}

BioinfRes SoSe17

ObjectsRevisited

BioinfRes SoSe17

ObjectswithSimilarBehaviour

●  Wewanttohaveobjectswithsimilarbehaviour

●  Wecanaddexpliciltyaddmethodstoeachobject

●  Wecanaddmethodsto`Object.prototype`

●  Isthereabegersolu)on?

BioinfRes SoSe17

ConstructorFunc)ons

●  Constructorfunc)onsallowtocreateagroupofobjectssuchthateachobjectbelongingtoagrouphassimilarbehaviour

< function Swordsman(name, hp, damage) { this.name = name; this.hp = hp; this.attacks = 2; this.damage = damage; }; var swordsman = new Swordsman('Arthur', 100, 40); swordsman > Swordsman {name: "Arthur", hp: 100, attacks: 2, damage: 40}

BioinfRes SoSe17

ConstructorFunc)ons

●  `new`keywordcreatesanewobject

●  Valueofthe`prototype`propertyoftheconstructorfunc)onbecomestheprototypeofthenewobject

●  `this`returnsthenewobjectinsidetheconstructorfunc)on

< Object.getPrototypeOf(swordsman) === Swordsman.prototype true

BioinfRes SoSe17

ConstructorFunc)ons

●  Eachfunc)on,includingconstructorfunc)ons,has`prototype`property

●  Valueof`prototype`propertyisanobject

●  Thisobjectbecomestheprototypeofeveryobjectcreatedbyacorrespondingconstructorfunc)on

< Swordsman.prototype.getTotalDamage = function() { return this.attacks * this.damage; } swordsman.getTotalDamage() > 80

BioinfRes SoSe17

AddingProper)estoaPrototype

●  Wecanaddproper)esofanytypeandnotjustfunc)ons

< Swordsman.prototype.house = 'Lannister'; swordsman.house > "Lannister"

BioinfRes SoSe17

NoAccessControl

●  Wenowknowenoughtowriteasimplevideogame

●  Inspired,wesatdowntoworkonit

●  Andsuddenlywerealizethatalloftheobject’sproper)esarepublic,arevisiblefromtheoutside

●  JavaScripthasnowayofdeclaringcertainproper)esasprivateorprotected,theyareallpublic

●  Ourswordsman’sdamageandagackstatsareexposedtotheoutsideworld

BioinfRes SoSe17

ClosuresasaSolu)on

●  Wecansolvethisproblemwithclosures

< function Swordsman(name, hp, damage) { this.name = name; this.hp = hp; var dmg = damage; var attacks = 2; this.getTotalDamage = function() { return attacks * dmg; }; }; var swordsman = new Swordsman('Arthur', 100, 40); swordsman.getTotalDamage(); > 80 < swordsman.dmg > undefined < swordsman.damage > undefined

BioinfRes SoSe17

ClosuresasaSolu)on

●  `dmg`and`agacks`variablesaredefinedintheconstructor

●  Thesevariablesareaccessibleinside`getTotalDamage`func)on

●  ThankstoclosuresthesevariablesexistevenaQerconstructorinvoca)onhasbeencompleted

●  Itisimpossibletoaccessthisvariablesfromtheoutside

●  Wecanmakeproper)esandmethods”private”thisway

BioinfRes SoSe17

AccessControlVSPrototypes

●  Closuresallowustolimitaccesstocertainproper)es

●  Everythinghasaprice,however

●  Wecan’taccesssuchproper)esinsidetheprototypemethods

●  Thus,wehavetochoosebetweenaccesscontrolwithclosuresandcodereusewithprototypechains

BioinfRes SoSe17

PrototypeChain?

●  Yes,achain

●  Wecancreateanobjectviaaconstructorfunc)on

●  Makethisobjectaprototypeofanotherobject< function Lannister() {}; Lannister.prototype.house = 'Lannister'; function Swordsman() {}; Swordsman.prototype = new Lannister; function Archer() {}; Archer.prototype = Swordsman.prototype; var swordsman = new Swordsman(); swordsman.house > "Lannister”

BioinfRes SoSe17

PrototypalInheritance

●  Whenweinvokeaspecificmethodonanobject

●  First,JavaScriptlooksforamethodwithagivennameintheobject

●  Then,inthatobject’sprototype

●  Then,inthatobject’sprototype’sprototype

●  …

●  Finally,in`Object.prototype`

BioinfRes SoSe17

DangersofConstructors

●  Constructorfunc)onisaregularfunc)on(nospecialkeywords,nonamingrestric)ons,etc.),it’seasytomixaconstructorfunc)onandaregularfunc)on

●  Error:callingaconstructorfunc)onwithout`new`(`this willnotbeboundtoanewobject)

●  Error:callingaregularfunc)onthatexplicitlyreturnsanobjectwith`new`(itwills)llreturnthatobject)

BioinfRes SoSe17

DangersofConstructors

< function Constructor() { this.name = 'Bioinformatics Resources'; }; var cls = Constructor(); cls > undefined < name > "Bioinformatics Resources"

●  Error:callingaconstructorfunc)onwithout`new`(`this isboundtotheglobalobject)

BioinfRes SoSe17

DangersofConstructors

< function Constructor() { return { name: 'Bioinformatics Resources’ } }; var cls = new Constructor(); Object.getPrototypeOf(cls) === Constructor.prototype; > false < Object.getPrototypeOf(cls) === Object.prototype; > true

●  Error:callingaregularfunc)onthatexplicitlyreturnsanobjectwith`new`(itwills)llreturnthatobject)

BioinfRes SoSe17

WrappingUp

●  5differentwaystocallafunc)onwithrespectto`this`:-  Func)oninvoca)on

-  Methodinvoca)on

-  Constructorinvoca)on

-  Indirectinvoca)onwith`apply`and`call`

-  Boundinvoca)onwith`bind`

BioinfRes SoSe17

Wrappingup

●  4waystocreateanobject:-  Default`Object`constructor

-  Objectliteral

-  User-definedconstructor

-  Closures

BioinfRes SoSe17

ConstructorvsClosure

●  Closuresallowtocontrolaccess

●  Prototypesallowtoreusecodeanduselessmemorybystoringproper)esandmethodsintheprototype

BioinfRes SoSe17

Object.create

●  ES5addedonemorewayofcrea)nganobject

●  `Object.create`takes`object1`asanargumentandreturns`object2`whoseprototypeis`object1`

●  Allowstocreateobjectswithuser-madeprototypeswithoutcrea)ngconstructors

< var lannister = {name: 'Lannister'}; < var swordsman = Object.create(lannister); < Object.getPrototypeOf(swordsman) === lannister; > true < swordsman.name > "Lannister"

BioinfRes SoSe17

Whybother?

●  WhydoweevenbotherwithJavaScript?

●  BecauseJavaScriptallowsustoworkwiththeDOM

BioinfRes SoSe17

DocumentObjectModel

●  TheDocumentObjectModel(DOM)isacross-pla^ormandlanguage-independentapplica)onprogramminginterfacethattreatsanHTML,XHTML,orXMLdocumentasatreestructurewhereineachnodeisanobjectrepresen)ngapartofthedocument.Theobjectscanbemanipulatedprogramma)callyandanyvisiblechangesoccurringasaresultmaythenbereflectedinthedisplayofthedocument.[1]

[1]Wikipedia,Document_Object_Model.Retrievedfromhgps://en.wikipedia.org/wiki/Document_Object_Model

BioinfRes SoSe17

DocumentObjectModel

BioinfRes SoSe17

TreeStructure

●  EachelementisanodeintheDOMtree

●  Eachdocumentelementhasanaddress

BioinfRes SoSe17

TraversingtheDOMTree

●  `document`istherootelementofthetree

●  foreachelement,wecangetit’schildrenwith`childNodes`

< document > #document < document.childNodes > [<!DOCTYPE html>, <html> <head> … </head> <body> … </body> </html> ] < document.childNodes[1].childNodes[2].childNodes[1] > <h1> Bioinformatics Resources </h1>

BioinfRes SoSe17

TraversingtheDOMTree

●  foreachelement,wecangetit’sparentwith`parentNode`

< var h1 = document.childNodes[1].childNodes[2].childNodes[1]; h1; > <h1> Bioinformatics Resources </h1> < h1.parentNode; > <body>…</body>

BioinfRes SoSe17

Manipula)ngDOMTree

●  Wecanretrieve,change,add,andremoveelements

BioinfRes SoSe17

RetrievingDOMElements

●  `getElementByID`returnsanelementwithaspecifiedidor`null`

●  Thisistooverboseforsuchafrequentopera)on

●  MorecompactwaywithjQuery–`$('#hello')`

< document.getElementById('hello'); > <div id="hello">Hello!</div> < $('#hello') > <div id="hello">Hello!</div>

BioinfRes SoSe17

RetrievingDOMElements

●  `getElementsByTagName`returnsanarrayofelementswithaspecifiedtag

●  jQueryversion–`$('tag')`

●  `getElementsByName`returnsanarrayofelementswithaspecifiedname(namesareusedonformelements)

●  jQueryversion–`$([name='name'])`

BioinfRes SoSe17

ChangingDOMElements

●  `innerText`propertyallowstochangecontentofanelement

●  jQueryversion–`$('selector')`.text('newtext')`

< document.getElementById('hello').innerText = 'Hi there!’ > "Hi there!" < $('#hello').text('Hello!') > [<div id= "hello"> Hello! </div> ]

BioinfRes SoSe17

Crea)ngDOMElements

●  Createanelementwith`createElement`andinsertitintotheDOMwith`appendChild`

●  jQueryversion–`$('selector').append($('<tag></tag>'));`

< var btn = document.createElement('button'); document.getElementById('main').appendChild(btn); > <button></button> < $('#main').append($('<button></button>')); > <div id="main">…<button></button></div>

BioinfRes SoSe17

RemovingDOMElements

●  `removeChild`removesagivenelementfromanelementitiscalledon

●  jQueryversion–`$('selector').remove`

< document.getElementById('third').parentNode .removeChild(document.getElementById('third')); > <div id= "third"> 3. </div> < $('#third').remove(); > [<div id= "third"> 3. </div> ]