兼容主流浏览器的jQuery+CSS 实现遮罩层的简单代码
在页面点击"注册"，出现一层有不透明度的黑色遮罩；遮罩层的上方是注册框；此时无法点击页面上除注册框外的其他元素；点击注册框上的"随便逛逛"，遮罩层消失。
预览地址：
http://jsfiddle.net/p2x3c7df/embedded/result/
要点：
1.注册框始终水平、垂直居中，包括鼠标滚轮上下滚动页面、缩放页面和调整浏览器窗口大小时
主要由CSS控制，注册框的宽度和高度都已经确定(620*420px)，首先使用position:fixed来使它相对于浏览器窗口绝对定位；然后使它垂直居中：top:50%;left:50%;margin:-210px00-310px;
2.当缩放页面和调整浏览器窗口大小时，遮罩层需始终覆盖整个文档和充满整个浏览器可视窗口以及需要滚动才能浏览到的部分，需要兼容Chrome和IE等不同内核浏览器；
两个重要的属性：js的window.screen.availHeight和jQuery的$(document.body).outerHeight(true)。window.screen.availHeight指屏幕可用工作区域的高，$(document.body).outerHeight(true)指浏览器当前窗口文档body的总宽度包括borderpaddingmargin。window.screen.availHeight主要用于IE(11)缩放页面后，遮罩层仍能充满浏览器窗口。
3.遮罩层出现时，页面仍可以上下滚动，但是无法操作页面中除登陆框外的其他元素
代码：
HTML(需测试足够高的文档)：
<divid="wrap">
<divid="rbox"><aclass="go"href="#"onclick="returnfalse;">先逛逛>></a></div>
<divid="mask"></div>
<divclass="content">
<divid="usertie">
<span>
<aid="register"href="#"onclick="returnfalse;">注册</a>
</span>
</div>
TheSuicide.
MeanwhileMonteCristohadalsoreturnedtotownwithEmmanuelandMaximilian.Theirreturnwascheerful.Emmanueldidnotconcealhisjoyatthepeacefulterminationoftheaffair,andwasloudinhisexpressionsofdelight.Morrel,inacornerofthecarriage,allowedhisbrother-in-law'sgayetytoexpenditselfinwords,whilehefeltequalinwardjoy,which,however,betrayeditselfonlyinhiscountenance.AttheBarriereduTronetheymetBertuccio,whowaswaitingthere,motionlessasasentinelathispost.MonteCristoputhisheadoutofthewindow,exchangedafewwordswithhiminalowtone,andthestewarddisappeared."Count,"saidEmmanuel,whentheywereattheendofthePlaceRoyale,"putmedownatmydoor,thatmywifemaynothaveasinglemomentofneedlessanxietyonmyaccountoryours."
"Ifitwerenotridiculoustomakeadisplayofourtriumph,Iwouldinvitethecounttoourhouse;besidesthat,hedoubtlesshassometremblinghearttocomfort.Sowewilltakeleaveofourfriend,andlethimhastenhome."
"Stopamoment,"saidMonteCristo;"donotletmelosebothmycompanions.Return,Emmanuel,toyourcharmingwife,andpresentmybestcomplimentstoher;anddoyou,Morrel,accompanymetotheChampsElysees."
"Willingly,"saidMaximilian;"particularlyasIhavebusinessinthatquarter."
"Shallwewaitbreakfastforyou?"askedEmmanuel.
"No,"repliedtheyoungman.Thedoorwasclosed,andthecarriageproceeded."SeewhatgoodfortuneIbroughtyou!"saidMorrel,whenhewasalonewiththecount."Haveyounotthoughtso?"
"Yes,"saidMonteCristo;"forthatreasonIwishedtokeepyounearme."
"Itismiraculous!"continuedMorrel,answeringhisownthoughts.
"What?"saidMonteCristo.
"Whathasjusthappened."
"Yes,"saidtheCount,"youareright--itismiraculous."
"ForAlbertisbrave,"resumedMorrel.
"Verybrave,"saidMonteCristo;"Ihaveseenhimsleepwithaswordsuspendedoverhishead."
"Sheisgoingtoleaveherhouse,"saidthesteward. "Andherson?" "Florentin,hisvalet,thinksheisgoingtodothesame." "Comethisway."MonteCristotookBertucciointohisstudy,wrotetheletterwehaveseen,andgaveittothesteward."Go,"saidhequickly."Butfirst,letHaideebeinformedthatIhavereturned." "HereIam,"saidtheyounggirl,whoatthesoundofthecarriagehadrundown-stairsandwhosefacewasradiantwithjoyatseeingthecountreturnsafely.Bertuccioleft.Everytransportofadaughterfindingafather,allthedelightofamistressseeinganadoredlover,werefeltbyHaideeduringthefirstmomentsofthismeeting,whichshehadsoeagerlyexpected.Doubtless,althoughlessevident,MonteCristo'sjoywasnotlessintense.Joytoheartswhichhavesufferedlongislikethedewonthegroundafteralongdrought;boththeheartandthegroundabsorbthatbeneficentmoisturefallingonthem,andnothingisoutwardlyapparent. MonteCristowasbeginningtothink,whathehadnotforalongtimedaredtobelieve,thatthereweretwoMercedesintheworld,andhemightyetbehappy.Hiseye,elatewithhappiness,wasreadingeagerlythetearfulgazeofHaidee,whensuddenlythedooropened.Thecountknithisbrow."M.deMorcerf!"saidBaptistin,asifthatnamesufficedforhisexcuse.Infact,thecount'sfacebrightened. "Which,"askedhe,"theviscountorthecount?" "Thecount." "Oh,"exclaimedHaidee,"isitnotyetover?" "Iknownotifitisfinished,mybelovedchild,"saidMonteCristo,takingtheyounggirl'shands;"butIdoknowyouhavenothingmoretofear." "Butitisthewretched"-- "Thatmancannotinjureme,Haidee,"saidMonteCristo;"itwashissonalonethattherewascausetofear." "AndwhatIhavesuffered,"saidtheyounggirl,"youshallneverknow,mylord."MonteCristosmiled."Bymyfather'stomb,"saidhe,extendinghishandovertheheadoftheyounggirl,"Isweartoyou,Haidee,thatifanymisfortunehappens,itwillnotbetome." Thedoorwaswideopen,ahackney-coachwasstandinginthemiddleoftheyard--astrangesightbeforesonobleamansion;thecountlookedatitwithterror,butwithoutdaringtoinquireitsmeaning,herushedtowardshisapartment.Twopersonswerecomingdownthestairs;hehadonlytimetocreepintoanalcovetoavoidthem.ItwasMercedesleaningonherson'sarmandleavingthehouse.Theypassedclosebytheunhappybeing,who,concealedbehindthedamaskcurtain,almostfeltMercedesdressbrushpasthim,andhisson'swarmbreath,pronouncingthesewords,--"Courage,mother!Come,thisisnolongerourhome!"Thewordsdiedaway,thestepswerelostinthedistance.Thegeneraldrewhimselfup,clingingtothecurtain;heutteredthemostdreadfulsobwhicheverescapedfromthebosomofafatherabandonedatthesametimebyhiswifeandson.Hesoonheardtheclatteroftheironstepofthehackney-coach,thenthecoachman'svoice,andthentherollingoftheheavyvehicleshookthewindows.Hedartedtohisbedroomtoseeoncemoreallhehadlovedintheworld;butthehackney-coachdroveonandtheheadofneitherMercedesnorhersonappearedatthewindowtotakealastlookatthehouseorthedesertedfatherandhusband.Andattheverymomentwhenthewheelsofthatcoachcrossedthegatewayareportwasheard,andathicksmokeescapedthroughoneofthepanesofthewindow,whichwasbrokenbytheexplosion. Thedoorwaswideopen,ahackney-coachwasstandinginthemiddleoftheyard--astrangesightbeforesonobleamansion;thecountlookedatitwithterror,butwithoutdaringtoinquireitsmeaning,herushedtowardshisapartment.Twopersonswerecomingdownthestairs;hehadonlytimetocreepintoanalcovetoavoidthem.ItwasMercedesleaningonherson'sarmandleavingthehouse.Theypassedclosebytheunhappybeing,who,concealedbehindthedamaskcurtain,almostfeltMercedesdressbrushpasthim,andhisson'swarmbreath,pronouncingthesewords,--"Courage,mother!Come,thisisnolongerourhome!"Thewordsdiedaway,thestepswerelostinthedistance.Thegeneraldrewhimselfup,clingingtothecurtain;heutteredthemostdreadfulsobwhicheverescapedfromthebosomofafatherabandonedatthesametimebyhiswifeandson.Hesoonheardtheclatteroftheironstepofthehackney-coach,thenthecoachman'svoice,andthentherollingoftheheavyvehicleshookthewindows.Hedartedtohisbedroomtoseeoncemoreallhehadlovedintheworld;butthehackney-coachdroveonandtheheadofneitherMercedesnorhersonappearedatthewindowtotakealastlookatthehouseorthedesertedfatherandhusband.Andattheverymomentwhenthewheelsofthatcoachcrossedthegatewayareportwasheard,andathicksmokeescapedthroughoneofthepanesofthewindow,whichwasbrokenbytheexplosion. </div> </div>
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