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1、外文原文Source:WebPageDesignUsingJavaScriptTHEBASICSJAVASCRIPTusesasubsetoftheprogramminglanguageJAVAtoprovideahighlevelofinteractivityonawebpage.JavaScriptsarestoredwithinanHTMLdocumentandareinterpretedbythewebbrowser.JavaScriptsmaybelocatedwithintheHTMLcodeatthepointinthepagewher

2、etheyaretoappearonthescreenortheymaybewrittenusingfunctions.FunctionsaresmallsubprogramsthatarestoredbetweentheheadtagsofanHTMLdocumentandarecaliedontobeexecutedwhenaparticulareventoccurs.WhetherthescriptisstoredbetweentheheadtagsorwithinthebodyoftheHTMLdocument,itmustbeenclose

3、dinscripttags.Also,asetofHTMLcommenttagsaretypicallyusedinsidethescripttagssothatolderbrowsersthatdonotsupportJavaScriptwillignorethescriptandcontinuetoprocessthepagewithouterrors.Followingisanexampleofthescriptandcommenttags:criptlanguage=Hjava-IncludeJavaScriptCodeHereript>Be

4、awarethatJavaScriptiscasesensitive...thedifferencebetweenaworkingscriptandanerrormessagecanbeonecapitalletter.ALERTBOXESTopopupanalertboxincludethefollowinglineofcodeinsideofscripttagsinthebodyofyourHTMLdocument.PleasenotethattheprocessingofthepagewilIstopuntiltheviewerresponds

5、tothealertbox.alert(HPlacethetexttobedisplayedinthealertboxbetweenthesequotes.1')Othertypesofpre-madedialogboxesareavailablesuchasthepromptandconfirmboxes.InordertotakefulIadvantageofthefeaturesofthesedialogboxesyoumustwritemoreJavaScriptcodewhichcanusethevaluesthatarereturnedb

6、ythedialogboxes.Thefollowingstatementswillpopupadialogboxthatrequiresayesornoanswer(OKorCancel).IftheanswerisOKthenthevariablenamedanswerhasavalueoftrueandiftheanswerisCanceIthenthevariablenamedanswerhasavalueoffaIse.YoucanthenuseanifstatementintheJavaScriptcodetorespondappropr

7、iately.varanswer=confirm("Areyousureyouwanttoquit?n)if(answer==true){window.close()}ThefollowingcodewiIIpopupadialogboxthataskstheusertoentersomesortofinformation.IftheuserclicksOKtheinformationtheyenteredisstoredinthevariable.Thesecondsetofquotationmarksinsideofthepromptstatem

8、entmakethecontentsofthetextboxblankwhenthedialogboxisd