This is a work in progress! For the latest updates from the HTML WG, possibly including important bug fixes, please look at the editor's draft instead.
The setTimeout()
and setInterval()
methods allow authors to schedule timer-based callbacks.
[Supplemental, NoInterfaceObject] interface WindowTimers { long setTimeout(in any handler, in optional any timeout, in any... args); void clearTimeout(in long handle); long setInterval(in any handler, in optional any timeout, in any... args); void clearInterval(in long handle); }; Window implements WindowTimers;
setTimeout
( handler [, timeout [, arguments ] ] )Schedules a timeout to run handler after timeout milliseconds. Any arguments are passed straight through to the handler.
setTimeout
( code [, timeout ] )Schedules a timeout to compile and run code after timeout milliseconds.
clearTimeout
( handle )Cancels the timeout set with setTimeout()
identified by handle.
setInterval
( handler [, timeout [, arguments ] ] )Schedules a timeout to run handler every timeout milliseconds. Any arguments are passed straight through to the handler.
setInterval
( code [, timeout ] )Schedules a timeout to compile and run code every timeout milliseconds.
clearInterval
( handle )Cancels the timeout set with setInterval()
identified by handle.
This API does not guarantee that timers will fire exactly on schedule. Delays due to CPU load, other tasks, etc, are to be expected.
The WindowTimers
interface adds to the
Window
interface and the WorkerUtils
interface (part of Web Workers).
Each object that implements the WindowTimers
interface has a list of active timeouts and a list
of active intervals. Each entry in these lists is identified
by a number, which must be unique within its list for the lifetime
of the object that implements the WindowTimers
interface.
The setTimeout()
method must run the following steps:
Let handle be a user-agent-defined integer that is greater than zero that will identify the timeout to be set by this call.
Add an entry to the list of active timeouts for handle.
Get the timed task handle in the list of active timeouts, and let task be the result.
Get the timeout, and let timeout be the result.
If the currently running task is a task that was created by the
setTimeout()
method, and timeout is less than 4, then
increase timeout to 4.
Return handle, and then continue running this algorithm asynchronously.
If the method context is a Window
object, wait until the Document
associated with the
method context has been fully active for
a further timeout milliseconds (not
necessarily consecutively).
Otherwise, if the method context is a
WorkerUtils
object, wait until timeout milliseconds have passed with the worker
not suspended (not necessarily consecutively).
Otherwise, act as described in the specification that defines
that the WindowTimers
interface is implemented by
some other object.
Wait until any invocations of this algorithm started before this one whose timeout is equal to or less than this one's have completed.
Optionally, wait a further user-agent defined length of time.
This is intended to allow user agents to pad timeouts as needed to optimise the power usage of the device. For example, some processors have a low-power mode where the granularity of timers is reduced; on such platforms, user agents can slow timers down to fit this schedule instead of requiring the processor to use the more accurate mode with its associated higher power usage.
The clearTimeout()
method must clear the entry identified as handle
from the list of active timeouts of the
WindowTimers
object on which the method was invoked,
where handle is the argument passed to the
method, if any. (If handle does not identify an
entry in the list of active timeouts of the
WindowTimers
object on which the method was invoked,
the method does nothing.)
The setInterval()
method must run the following steps:
Let handle be a user-agent-defined integer that is greater than zero that will identify the interval to be set by this call.
Add an entry to the list of active intervals for handle.
Get the timed task handle in the list of active intervals, and let task be the result.
Get the timeout, and let timeout be the result.
If timeout is less than 10, then increase timeout to 10.
Return handle, and then continue running this algorithm asynchronously.
Wait: If the method context is a
Window
object, wait until the Document
associated with the method context has been fully
active for a further interval
milliseconds (not necessarily consecutively).
Otherwise, if the method context is a
WorkerUtils
object, wait until interval milliseconds have passed with the worker
not suspended (not necessarily consecutively).
Otherwise, act as described in the specification that defines
that the WindowTimers
interface is implemented by
some other object.
Optionally, wait a further user-agent defined length of time.
This is intended to allow user agents to pad timeouts as needed to optimise the power usage of the device. For example, some processors have a low-power mode where the granularity of timers is reduced; on such platforms, user agents can slow timers down to fit this schedule instead of requiring the processor to use the more accurate mode with its associated higher power usage.
Return to the step labeled wait.
The clearInterval()
method must clear the entry identified as handle
from the list of active intervals of the
WindowTimers
object on which the method was invoked,
where handle is the argument passed to the
method, if any. (If handle does not identify an
entry in the list of active intervals of the
WindowTimers
object on which the method was invoked,
the method does nothing.)
The method context, when referenced by the algorithms
in this section, is the object on which the method for which the
algorithm is running is implemented (a Window
or
WorkerUtils
object).
When the above methods are invoked and try to get the timed task handle in list list, they must run the following steps:
If the first argument to the invoked method is an object that has an internal [[Call]] method, then return a task that checks if the entry for handle in list has been cleared, and if it has not, calls the aforementioned [[Call]] method with as its arguments the third and subsequent arguments to the invoked method (if any), and abort these steps.
Otherwise, continue with the remaining steps.
Apply the ToString() abstract operation to the first argument to the method, and let script source be the result. [ECMA262]
Let script language be JavaScript.
If the method context is a Window
object, let global object be the method
context, let browsing context be the
browsing context with which global
object is associated, let character
encoding be the character encoding of the Document
associated with global object (this is a reference, not a copy), and let
base URL be the base URL of the Document
associated with
global object (this is
a reference, not a copy).
Otherwise, if the method context is a
WorkerUtils
object, let global
object, browsing context, document, character encoding,
and base URL be the script's global
object, script's browsing context,
script's document, script's URL character
encoding, and script's base URL (respectively)
of the script that the
run a worker algorithm created when it created the
method context.
Otherwise, act as described in the specification that defines
that the WindowTimers
interface is implemented by
some other object.
Return a task that checks if the entry for handle in list has been cleared, and if it has not, creates a script using script source as the script source, scripting language as the scripting language, global object as the global object, browsing context as the browsing context, document as the document, character encoding as the URL character encoding, and base URL as the base URL.
When the above methods are to get the timeout, they must run the following steps:
Let timeout be the second argument to the method, or zero if the argument was omitted.
Apply the ToString() abstract operation to timeout, and let timeout be the result. [ECMA262]
Apply the ToNumber() abstract operation to timeout, and let timeout be the result. [ECMA262]
If timeout is an Infinity value, a Not-a-Number (NaN) value, or negative, let timeout be zero.
Round timeout down to the nearest integer, and let timeout be the result.
Return timeout.
The task source for these tasks is the timer task source.
alert
(message)Displays a modal alert with the given message, and waits for the user to dismiss it.
A call to the navigator.yieldForStorageUpdates()
method is implied when this method is invoked.
confirm
(message)Displays a modal OK/Cancel prompt with the given message, waits for the user to dismiss it, and returns true if the user clicks OK and false if the user clicks Cancel.
A call to the navigator.yieldForStorageUpdates()
method is implied when this method is invoked.
prompt
(message [, default] )Displays a modal text field prompt with the given message, waits for the user to dismiss it, and returns the value that the user entered. If the user cancels the prompt, then returns null instead. If the second argument is present, then the given value is used as a default.
A call to the navigator.yieldForStorageUpdates()
method is implied when this method is invoked.
The alert(message)
method, when invoked, must
release the storage mutex and show the given message to the user. The user agent may make the
method wait for the user to acknowledge the message before
returning; if so, the user agent must pause while the
method is waiting.
The confirm(message)
method, when invoked, must
release the storage mutex and show the given message to the user, and ask the user to respond with
a positive or negative response. The user agent must then
pause as the method waits for the user's response. If
the user responds positively, the method must return true, and if
the user responds negatively, the method must return false.
The prompt(message, default)
method, when invoked, must release the storage mutex,
show the given message to the user, and ask the
user to either respond with a string value or abort. The user agent
must then pause as the method waits for the user's
response. The second argument is optional. If the second argument
(default) is present, then the response must be
defaulted to the value given by default. If the
user aborts, then the method must return null; otherwise, the method
must return the string that the user responded with.
print
()Prompts the user to print the page.
A call to the navigator.yieldForStorageUpdates()
method is implied when this method is invoked.
The print()
method,
when invoked, must run the printing steps.
User agents should also run the printing steps whenever the user asks for the opportunity to obtain a physical form (e.g. printed copy), or the representation of a physical form (e.g. PDF copy), of a document.
The printing steps are as follows:
The user agent may display a message to the user and/or may abort these steps.
For instance, a kiosk browser could silently
ignore any invocations of the print()
method.
For instance, a browser on a mobile device could detect that there are no printers in the vicinity and display a message saying so before continuing to offer a "save to PDF" option.
The user agent must fire a simple event named
beforeprint
at the
Window
object of the Document
that is
being printed, as well as any nested browsing contexts in it.
The beforeprint
event can be used
to annotate the printed copy, for instance adding the time at
which the document was printed.
The user agent must release the storage mutex.
The user agent should offer the user the opportunity to obtain a physical form (or the representation of a physical form) of the document. The user agent may wait for the user to either accept or decline before returning; if so, the user agent must pause while the method is waiting. Even if the user agent doesn't wait at this point, the user agent must use the state of the relevant documents as they are at this point in the algorithm if and when it eventually creates the alternate form.
The user agent must fire a simple event named
afterprint
at the
Window
object of the Document
that is
being printed, as well as any nested browsing contexts in it.
The afterprint
event can be used
to revert annotations added in the earlier event, as well as
showing post-printing UI. For instance, if a page is walking the
user through the steps of applying for a home loan, the script
could automatically advance to the next step after having printed
a form or other.
showModalDialog
(url [, argument] )Prompts the user with the given page, waits for that page to close, and returns the return value.
A call to the navigator.yieldForStorageUpdates()
method is implied when this method is invoked.
The showModalDialog(url, argument)
method, when invoked, must
cause the user agent to run the following steps:
Resolve url relative to the entry script's base URL.
If this fails, then throw a SYNTAX_ERR
exception
and abort these steps.
Release the storage mutex.
If the user agent is configured such that this invocation of
showModalDialog()
is
somehow disabled, then return the empty string and abort these
steps.
User agents are expected to disable this method in certain cases to avoid user annoyance (e.g. as part of their popup blocker feature). For instance, a user agent could require that a site be white-listed before enabling this method, or the user agent could be configured to only allow one modal dialog at a time.
Let the list of background browsing contexts be a list of all the browsing contexts that:
Window
object on which the showModalDialog()
method was
called, and thatshowModalDialog()
method at
the time the method was called,...as well as any browsing contexts that are nested inside any of the browsing contexts matching those conditions.
Disable the user interface for all the browsing contexts in the list of background browsing contexts. This should prevent the user from navigating those browsing contexts, causing events to be sent to those browsing context, or editing any content in those browsing contexts. However, it does not prevent those browsing contexts from receiving events from sources other than the user, from running scripts, from running animations, and so forth.
Create a new auxiliary browsing context, with the
opener browsing context being the browsing context of
the Window
object on which the showModalDialog()
method was
called. The new auxiliary browsing context has no name.
This browsing context's
Document
s' Window
objects all implement
the WindowModal
interface.
Let the dialog arguments of the new browsing context be set to the value of argument, or the 'undefined' value if the argument was omitted.
Let the dialog arguments' origin be the
origin of the script that called the showModalDialog()
method.
Navigate the new browsing context to the absolute URL that resulted from resolving url earlier, with replacement enabled, and with the browsing context of the script that invoked the method as the source browsing context.
Spin the event loop until the new browsing context is closed. (The user agent must allow the user to indicate that the browsing context is to be closed.)
Reenable the user interface for all the browsing contexts in the list of background browsing contexts.
Return the auxiliary browsing context's return value.
The Window
objects of Document
s hosted
by browsing contexts created
by the above algorithm must all have the WindowModal
interface added to their Window
interface:
[Supplemental, NoInterfaceObject] interface WindowModal { readonly attribute any dialogArguments; attribute DOMString returnValue; };
dialogArguments
Returns the argument argument that was
passed to the showModalDialog()
method.
returnValue
[ = value ]Returns the current return value for the window.
Can be set, to change the value that will be returned by the
showModalDialog()
method.
Such browsing contexts have associated dialog
arguments, which are stored along with the dialog
arguments' origin. These values are set by the showModalDialog()
method in the
algorithm above, when the browsing context is created, based on the
arguments provided to the method.
The dialogArguments
IDL attribute, on getting, must check whether its browsing context's
active document's origin is the same as the dialog arguments'
origin. If it is, then the browsing context's dialog
arguments must be returned unchanged. Otherwise, if the
dialog arguments are an object, then the empty string
must be returned, and if the dialog arguments are not
an object, then the stringification of the dialog
arguments must be returned.
These browsing contexts also have an associated return value. The return value of a browsing context must be initialized to the empty string when the browsing context is created.
The returnValue
IDL attribute, on getting, must return the return value
of its browsing context, and on setting, must set the return
value to the given new value.
The window.close()
method can be used to
close the browsing context.
Navigator
objectThe navigator
attribute of the Window
interface must return an
instance of the Navigator
interface, which represents
the identity and state of the user agent (the client), and allows
Web pages to register themselves as potential protocol and content
handlers:
interface Navigator { // objects implementing this interface also implement the interfaces given below }; Navigator implements NavigatorID; Navigator implements NavigatorOnLine; Navigator implements NavigatorAbilities; [Supplemental, NoInterfaceObject] interface NavigatorID { readonly attribute DOMString appName; readonly attribute DOMString appVersion; readonly attribute DOMString platform; readonly attribute DOMString userAgent; }; [Supplemental, NoInterfaceObject] interface NavigatorOnLine { readonly attribute boolean onLine; }; [Supplemental, NoInterfaceObject] interface NavigatorAbilities { // content handler registration void registerProtocolHandler(in DOMString scheme, in DOMString url, in DOMString title); void registerContentHandler(in DOMString mimeType, in DOMString url, in DOMString title); void yieldForStorageUpdates(); };
These interfaces are defined separately so that other
specifications can re-use parts of the Navigator
interface.
In certain cases, despite the best efforts of the entire industry, Web browsers have bugs and limitations that Web authors are forced to work around.
This section defines a collection of attributes that can be used to determine, from script, the kind of user agent in use, in order to work around these issues.
Client detection should always be limited to detecting known current versions; future versions and unknown versions should always be assumed to be fully compliant.
navigator
. appName
Returns the name of the browser.
navigator
. appVersion
Returns the version of the browser.
navigator
. platform
Returns the name of the platform.
navigator
. userAgent
Returns the complete User-Agent header.
appName
Must return either the string "Netscape
" or the full name of the browser, e.g. "Mellblom Browsernator
".
appVersion
Must return either the string "4.0
" or a string representing the version of the browser in detail, e.g. "1.0 (VMS; en-US) Mellblomenator/9000
".
platform
Must return either the empty string or a string representing the platform on which the browser is executing, e.g. "MacIntel
", "Win32
", "FreeBSD i386
", "WebTV OS
".
userAgent
Must return the string used for the value of the "User-Agent
" header in HTTP requests, or the empty string if no such header is ever sent.
Any information in this API that varies from user to user can be used to profile the user. In fact, if enough such information is available, a user can actually be uniquely identified. For this reason, user agent implementors are strongly urged to include as little information in this API as possible.
The registerProtocolHandler()
method allows Web sites to register themselves as possible handlers
for particular schemes. For example, an online telephone messaging
service could register itself as a handler of the sms:
scheme ([RFC5724]), so that if the user
clicks on such a link, he is given the opportunity to use that Web
site. Analogously, the registerContentHandler()
method allows Web sites to register themselves as possible handlers
for content in a particular MIME type. For example, the
same online telephone messaging service could register itself as a
handler for text/directory
files ([RFC2425]), so that if the user has no
native application capable of handling vCards ([RFC2426]), his Web browser can instead
suggest he use that site to view contact information stored on
vCards that he opens.
navigator
. registerProtocolHandler
(scheme, url, title)navigator
. registerContentHandler
(mimeType, url, title)Registers a handler for the given scheme or content type, at the given URL, with the given title.
The string "%s
" in the URL is used as a
placeholder for where to put the URL of the content to be
handled.
Throws a SECURITY_ERR
exception if the user agent
blocks the registration (this might happen if trying to register
as a handler for "http", for instance).
Throws a SYNTAX_ERR
if the "%s
" string is missing in the URL.
User agents may, within the constraints described in this section, do whatever they like when the methods are called. A UA could, for instance, prompt the user and offer the user the opportunity to add the site to a shortlist of handlers, or make the handlers his default, or cancel the request. UAs could provide such a UI through modal UI or through a non-modal transient notification interface. UAs could also simply silently collect the information, providing it only when relevant to the user.
User agents should keep track of which sites have registered handlers (even if the user has declined such registrations) so that the user is not repeatedly prompted with the same request.
The arguments to the methods have the following meanings and corresponding implementation requirements:
registerProtocolHandler()
only)A scheme, such as ftp
or sms
. The
scheme must be compared in an ASCII case-insensitive
manner by user agents for the purposes of comparing with the
scheme part of URLs that they consider against the list of
registered handlers.
The scheme value, if it contains a colon
(as in "ftp:
"), will never match anything, since
schemes don't contain colons.
This feature is not intended to be used with non-standard protocols.
registerContentHandler()
only)A MIME type, such as
model/vnd.flatland.3dml
or
application/vnd.google-earth.kml+xml
. The MIME
type must be compared in an ASCII
case-insensitive manner by user agents for the purposes of
comparing with MIME types of documents that they consider against
the list of registered handlers.
User agents must compare the given values only to the MIME type/subtype parts of content types, not to the complete type including parameters. Thus, if mimeType values passed to this method include characters such as commas or whitespace, or include MIME parameters, then the handler being registered will never be used.
The type is compared to the MIME type used by the user agent after the sniffing algorithms have been applied.
A string used to build the URL of the page that will handle the requests.
When the user agent uses this URL, it must replace the first
occurrence of the exact literal string "%s
"
with an escaped version of the absolute URL of the
content in question (as defined below), then resolve the resulting URL, relative to the base URL of the entry
script at the time the registerContentHandler()
or registerProtocolHandler()
methods were invoked, and then navigate an appropriate browsing context to the
resulting URL using the GET method (or equivalent for
non-HTTP URLs).
To get the escaped version of the absolute URL of the content in question, the user agent must replace every character in that absolute URL that doesn't match the <query> production defined in RFC 3986 by the percent-encoded form of that character. [RFC3986]
If the user had visited a site at http://example.com/
that made the following
call:
navigator.registerContentHandler('application/x-soup', 'soup?url=%s', 'SoupWeb™')
...and then, much later, while visiting http://www.example.net/
, clicked on a link such
as:
<a href="chickenkïwi.soup">Download our Chicken Kïwi soup!</a>
...then, assuming this chickenkïwi.soup
file
was served with the MIME type
application/x-soup
, the UA might navigate to the
following URL:
http://example.com/soup?url=http://www.example.net/chickenk%C3%AFwi.soup
This site could then fetch the chickenkïwi.soup
file and do whatever it is that it does with soup (synthesize it
and ship it to the user, or whatever).
A descriptive title of the handler, which the UA might use to remind the user what the site in question is.
User agents should raise SECURITY_ERR
exceptions if
the methods are called with scheme or mimeType values that the UA deems to be
"privileged". For example, a site attempting to register a handler
for http
URLs or text/html
content in a
Web browser would likely cause an exception to be raised.
User agents must raise a SYNTAX_ERR
exception if the
url argument passed to one of these methods does
not contain the exact literal string "%s
", or if resolving the url
argument with the first occurrence of the string "%s
" removed, relative to the entry
script's base URL, is
not successful.
User agents must not raise any other exceptions (other than binding-specific exceptions, such as for an incorrect number of arguments in an JavaScript implementation).
This section does not define how the pages registered by these methods are used, beyond the requirements on how to process the url value (see above). To some extent, the processing model for navigating across documents defines some cases where these methods are relevant, but in general UAs may use this information wherever they would otherwise consider handing content to native plugins or helper applications.
UAs must not use registered content handlers to handle content that was returned as part of a non-GET transaction (or rather, as part of any non-idempotent transaction), as the remote site would not be able to fetch the same data.
These mechanisms can introduce a number of concerns, in particular privacy concerns.
Hijacking all Web usage. User agents should not
allow schemes that are key to its normal operation, such as
http
or https
, to be rerouted through
third-party sites. This would allow a user's activities to be
trivially tracked, and would allow user information, even in secure
connections, to be collected.
Hijacking defaults. It is strongly recommended that user agents do not automatically change any defaults, as this could lead the user to send data to remote hosts that the user is not expecting. New handlers registering themselves should never automatically cause those sites to be used.
Registration spamming. User agents should
consider the possibility that a site will attempt to register a
large number of handlers, possibly from multiple domains (e.g. by
redirecting through a series of pages each on a different domain,
and each registering a handler for video/mpeg
—
analogous practices abusing other Web browser features have been
used by pornography Web sites for many years). User agents should
gracefully handle such hostile attempts, protecting the user.
Misleading titles. User agents should not rely
wholly on the title argument to the methods when
presenting the registered handlers to the user, since sites could
easily lie. For example, a site hostile.example.net
could claim that it was registering the "Cuddly Bear Happy Content
Handler". User agents should therefore use the handler's domain in
any UI along with any title.
Hostile handler metadata. User agents should protect against typical attacks against strings embedded in their interface, for example ensuring that markup or escape characters in such strings are not executed, that null bytes are properly handled, that over-long strings do not cause crashes or buffer overruns, and so forth.
Leaking Intranet URLs. The mechanism described in this section can result in secret Intranet URLs being leaked, in the following manner:
No actual confidential file data is leaked in this manner, but
the URLs themselves could contain confidential information. For
example, the URL could be
http://www.corp.example.com/upcoming-aquisitions/the-sample-company.egf
,
which might tell the third party that Example Corporation is
intending to merge with The Sample Company. Implementors might wish
to consider allowing administrators to disable this feature for
certain subdomains, content types, or schemes.
Leaking secure URLs. User agents should not send
HTTPS URLs to third-party sites registered as content handlers, in
the same way that user agents do not send Referer
(sic) HTTP headers from secure
sites to third-party sites.
Leaking credentials. User agents must never send username or password information in the URLs that are escaped and included sent to the handler sites. User agents may even avoid attempting to pass to Web-based handlers the URLs of resources that are known to require authentication to access, as such sites would be unable to access the resources in question without prompting the user for credentials themselves (a practice that would require the user to know whether to trust the third-party handler, a decision many users are unable to make or even understand).
This section is non-normative.
A simple implementation of this feature for a desktop Web browser might work as follows.
The registerContentHandler()
method could display a modal dialog box:
In this dialog box, "Kittens at work" is the title of the page
that invoked the method, "http://kittens.example.org/" is the URL of
that page, "application/x-meowmeow" is the string that was passed to
the registerContentHandler()
method as its first argument (mimeType),
"http://kittens.example.org/?show=%s" was the second argument (url), and "Kittens-at-work displayer" was the third
argument (title).
If the user clicks the Cancel button, then nothing further happens. If the user clicks the "Trust" button, then the handler is remembered.
When the user then attempts to fetch a URL that uses the "application/x-meowmeow" MIME type, then it might display a dialog as follows:
In this dialog, the third option is the one that was primed by the site registering itself earlier.
If the user does select that option, then the browser, in accordance with the requirements described in the previous two sections, will redirect the user to "http://kittens.example.org/?show=data%3Aapplication/x-meowmeow;base64,S2l0dGVucyBhcmUgdGhlIGN1dGVzdCE%253D".
The registerProtocolHandler()
method would work equivalently, but for schemes instead of unknown
content types.
navigator
. yieldForStorageUpdates
()If a script uses the document.cookie
API, or the
localStorage
API, the
browser will block other scripts from accessing cookies or storage
until the first script finishes.
[WEBSTORAGE]
Calling the navigator.yieldForStorageUpdates()
method tells the user agent to unblock any other scripts that may
be blocked, even though the script hasn't returned.
Values of cookies and items in the Storage
objects
of localStorage
attributes
can change after calling this method, whence its name.
[WEBSTORAGE]
The yieldForStorageUpdates()
method, when invoked, must, if the storage mutex is
owned by the event loop of the task that resulted in the method being
called, release the storage mutex so that it is once
again free. Otherwise, it must do nothing.