HTML: The Living Standard

Developer's Edition — Last Updated 14 September 2017

About this specification

This specification is like no other — it has been processed with you, the humble web developer, in mind.

The focus of this specification is readability and ease of access. Unlike the full HTML Standard, this "developer's edition" removes information that only browser vendors need know. It is automatically produced from the full specification by our build tooling, and thus always in sync with the latest developments in HTML.

To read about its conception, construction, and future, read the original press release, and the blog post about its relaunch.

Finally, feel free to contribute on GitHub to make this edition better for everyone!

1. 8.7 System state and capabilities
  1. 8.7.1 The Navigator object

8.7 System state and capabilities

8.7.1 The `Navigator` object

8.7.1.1 Client identification

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.

self . navigator . appCodeName: Returns the string "Mozilla".
self . navigator . appName: Returns the string "Netscape".
self . navigator . appVersion: Returns the version of the browser.
self . navigator . platform: Returns the name of the platform.
self . navigator . product: Returns the string "Gecko".
window . navigator . productSub: Returns either the string "20030107", or the string "20100101".
self . navigator . userAgent: Returns the complete `User-Agent` header.
window . navigator . vendor: Returns either the empty string, the string "Apple Computer, Inc.", or the string "Google Inc.".
window . navigator . vendorSub: Returns the empty string.

8.7.1.2 Language preferences

self . navigator . language

Returns a language tag representing the user's preferred language.

self . navigator . languages

Returns an array of language tags representing the user's preferred languages, with the most preferred language first.

The most preferred language is the one returned by navigator.language.

A languagechange event is fired at the Window or WorkerGlobalScope object when the user agent's understanding of what the user's preferred languages are changes.

8.7.1.3 Custom scheme and content handlers: the `registerProtocolHandler()` and `registerContentHandler()` methods

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, so that if the user clicks on such a link, they are 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/vcard files, so that if the user has no native application capable of handling vCards, their Web browser can instead suggest they use that site to view contact information stored on vCards that they open. [SMS] [RFC6350]

window . navigator . registerProtocolHandler(scheme, url, title)

window . 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 "SecurityError" DOMException if the user agent blocks the registration (this might happen if trying to register as a handler for "http", for instance).

Throws a "SyntaxError" DOMException if the "%s" string is missing in the URL.

In addition to the registration methods, there are also methods for determining if particular handlers have been registered, and for unregistering handlers.

state = window . navigator . isProtocolHandlerRegistered(scheme, url)

state = window . navigator . isContentHandlerRegistered(mimeType, url)

Returns one of the following strings describing the state of the handler given by the arguments:

new: Indicates that no attempt has been made to register the given handler (or that the handler has been unregistered). It would be appropriate to promote the availability of the handler or to just automatically register the handler.
registered: Indicates that the given handler has been registered or that the site is blocked from registering the handler. Trying to register the handler again would have no effect.
declined: Indicates that the given handler has been offered but was rejected. Trying to register the handler again may prompt the user again.

window . navigator . unregisterProtocolHandler(scheme, url)

window . navigator . unregisterContentHandler(mimeType, url)

Unregisters the handler given by the arguments.

8.7.1.4 Cookies

window . navigator . cookieEnabled: Returns false if setting a cookie will be ignored, and true otherwise.

8.7.1.5 Plugins

window . navigator . plugins . refresh( [ refresh ] ): Updates the lists of supported plugins and MIME types for this page, and reloads the page if the lists have changed.
window . navigator . plugins . length: Returns the number of plugins, represented by Plugin objects, that the user agent reports.
plugin = window . navigator . plugins . item(index)
window . navigator . plugins[index]: Returns the specified Plugin object.
plugin = window . navigator . plugins . item(name)
window . navigator . plugins[name]: Returns the Plugin object for the plugin with the given name.
window . navigator . mimeTypes . length: Returns the number of MIME types, represented by MimeType objects, supported by the plugins that the user agent reports.
mimeType = window . navigator . mimeTypes . item(index)
window . navigator . mimeTypes[index]: Returns the specified MimeType object.
mimeType = window . navigator . mimeTypes . item(name)
window . navigator . mimeTypes[name]: Returns the MimeType object for the given MIME type.
plugin . name: Returns the plugin's name.
plugin . description: Returns the plugin's description.
plugin . filename: Returns the plugin library's filename, if applicable on the current platform.
plugin . length: Returns the number of MIME types, represented by MimeType objects, supported by the plugin.
mimeType = plugin . item(index)
plugin[index]: Returns the specified MimeType object.
mimeType = plugin . item(name)
plugin[name]: Returns the MimeType object for the given MIME type.
mimeType . type: Returns the MIME type.
mimeType . description: Returns the MIME type's description.
mimeType . suffixes: Returns the MIME type's typical file extensions, in a comma-separated list.
mimeType . enabledPlugin: Returns the Plugin object that implements this MIME type.
window . navigator . javaEnabled(): Returns true if there's a plugin that supports the MIME type "application/x-java-vm".