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1、Chapter9JavaScriptandDHTML1ObjectivesExplainthe3layersofaWebdocument.InsertJavaScriptcodeonaWebpage.ExplainbasicJavaScriptsyntax.ExplainobjectsandJavaScriptobjects.ExplainDOM.Usecommonobjectssuchasdocument,window,form.Describetheeventhandlingmechanism.ExplainDHTML.ApplysimpleDHTMLonyourpages.2WhyJ
2、avaScript?AWebpagethatissemanticallymarkedupandbeautifullydesignediswonderful,buttoreallymakeitanexperience,itneedssomeinteractivity.The3-layer:structural,presentationandbehavioral.3WhatisJavaScript?JavaScriptisaprogramminglanguagemainlyusedontheWeb.JavaScriptisnotJava.JavaScriptcanbeusedtotestbro
3、wsers,respondtouseractivities,validateformdata,anddisplaycustomizedcontent(suchasfloatinganimation).4JavaScriptDosandDon’tsLikemanytools,JavaScriptcanbeusedforgoodorevil.TheevilusesofJavaScriptareallaround:rapid-firepop-upsthatopenfasterthanyoucanclosethem,sitesthatautomaticallysetthemselvesasyour
4、homepage,thelistgoesonandon.AsWebprofessionals,wehaveadutytomaketheuserexperienceaspositiveaspossibleandmakeoursitesbothusableandaccessible.JavaScriptshouldbeusedinsuchaswaythatapageorsitecanbeusedwithoutit.5UsingJavaScriptJavaScriptcanbeimplementedonasinglepageoronanentiresite.AswithCSS,itcanbeem
5、beddedinadocument,orexternalizedfromthatdocument.Seepage161.embeddedintheheadelementembeddedintagslinkedfromanexternalfile6SkillsNeededinProgrammingThefirsthardthingaboutprogrammingistolearn,becomecomfortablewith,andacceptsomeartificialmechanisms,whethertheymake“sense”toyouornot.AttentiontodetailS
6、tupidityGoodmemoryAbilitytoabstract,thinkonseverallevels7AttentiontodetailInprogramming,thedetailsmatter.Youcan'tbevague;youcan'tdescribeyourprogram3/4ofthewayandthensay“YouknowwhatImean?”andhavethecompilerfigureouttherest.Youhavetodotyouri'sandcrossyourt's.Ifthelanguagesaysyouhavetodeclarevariabl
7、esbeforeusingthem,youhaveto.8StupidityComputersareincrediblystupid.Theydoexactlywhatyoutellthemtodo:nomore,noless.Whenyou'reprogramming,ithelpstobeableto“think”asstupidlyasthecomputerdoes,sothatyou'reintherightfr
