在navigator.onLine 属性更改并变为 false时，在 body或冒泡到body上的offline事件被触发。
false时，
offline
Document
Document()
alinkColor
anchors
applets
async
bgColor
body
characterSet
childElementCount
children
compatMode
contentType
currentScript
defaultView
designMode
dir
doctype
documentElement
documentURI
documentURIObject
domain
domConfig
embeds
fgColor
firstElementChild
forms
mozFullScreen
mozFullScreenEnabled
head
height
hidden
images
implementation
lastElementChild
lastModified
lastStyleSheetSet
linkColor
links
location
mozSyntheticDocument
onabort
onafterscriptexecute
onanimationcancel
onanimationend
onanimationiteration
onauxclick
onbeforescriptexecute
onblur
oncancel
oncanplay
oncanplaythrough
onchange
onclick
onclose
oncontextmenu
oncuechange
ondblclick
ondurationchange
onended
onerror
onfocus
onfullscreenchange
onfullscreenerror
ongotpointercapture
oninput
oninvalid
onkeydown
onkeypress
onkeyup
onload
onloadeddata
onloadedmetadata
onloadend
onloadstart
onlostpointercapture
onmousedown
onmouseenter
onmouseleave
onmousemove
onmouseout
onmouseover
onmouseup
onoffline
ononline
onpause
onplay
onpointercancel
onpointerdown
onpointerenter
onpointerleave
onpointermove
onpointerout
onpointerover
onpointerup
onreset
onresize
onscroll
onselect
onselectionchange
onselectstart
onsubmit
ontouchcancel
ontouchstart
ontransitioncancel
ontransitionend
onvisibilitychange
onwheel
origin
plugins
policy
popupNode
preferredStyleSheetSet
readyState
referrer
scripts
scrollingElement
selectedStyleSheetSet
styleSheetSets
timeline
title
tooltipNode
URL
visibilityState
vlinkColor
width
xmlEncoding
xmlVersion
adoptNode()
append()
caretRangeFromPoint()
clear()
close
createAttribute
createCDATASection()
createComment
createDocumentFragment()
createElement()
createElementNS()
createEntityReference()
createEvent()
createExpression
createExpression()
createNodeIterator()
createNSResolver()
createProcessingInstruction()
createRange()
createTextNode
createTouch()
createTouchList()
createTreeWalker()
enableStyleSheetsForSet()
evaluate
evaluate()
execCommand
exitFullscreen()
exitPointerLock()
getAnimations()
getBoxObjectFor()
getElementById
getElementsByClassName()
getElementsByName()
getElementsByTagName()
getElementsByTagNameNS()
hasFocus
hasStorageAccess()
importNode
mozSetImageElement()
open()
prepend()
queryCommandEnabled()
queryCommandSupported()
querySelector()
querySelectorAll
querySelectorAll()
registerElement()
releaseCapture
requestStorageAccess()
write
writeln
Node
EventTarget
AbortController
AbortSignal
Attr
ByteString
CDATASection
CSSPrimitiveValue
CSSValue
CSSValueList
CharacterData
ChildNode
Comment
CustomEvent
DOMConfiguration
DOMError
DOMErrorHandler
DOMException
DOMImplementation
DOMImplementationList
DOMImplementationRegistry
DOMImplementationSource
DOMLocator
DOMObject
DOMParser
DOMPoint
DOMPointInit
DOMPointReadOnly
DOMRect
DOMString
DOMTimeStamp
DOMTokenList
DOMUserData
DocumentFragment
DocumentType
Element
ElementTraversal
Entity
EntityReference
Event
HTMLCollection
MutationObserver
NodeFilter
NodeIterator
NodeList
NonDocumentTypeChildNode
ProcessingInstruction
PromiseResolver
Range
Text
TextDecoder
TextEncoder
TimeRanges
TreeWalker
TypeInfo
USVString
UserDataHandler
XMLDocument