hasFeature (W3C DOM Core method)

Spec
Version Depr. Static
DOM1 No No
Browser support (more…)
IE6+ FF1.5+ SA1.3+ OP9+
Full Full Full Full
Returns
Boolean

Example

var supported = document.implementation.hasFeature('Events', '2.0')

In the example above, the variable supported will have the value true if the implementation supports the DOM 2 Events module. Otherwise supported will have the value false.

Arguments

feature (DOMString) required

The name of the feature to test, using one of the values defined in the DOM 2 Conformance list.

version (DOMString) required

The DOM version to test. For DOM 2 this is always the value 2.0. If this argument is empty the method will return true if the feature is supported at any DOM level.

Description

Test whether a specific feature of the DOM is implemented.

Here's a list of the features and DOM versions that can be tested:

Table 1. DOM features and versions that can be tested with hasFeature
Feature name Version Description
XML 1.0 DOM 1 Core and XML
HTML 1.0 DOM 1 Core and HTML
Core 2.0 DOM 2 Core
XML 2.0 DOM 2 XML
HTML 2.0 DOM 2 HTML
Views 2.0 DOM 2 Views module
StyleSheets 2.0 DOM 2 Style Sheets module
CSS 2.0 DOM 2 CSS module
CSS2 2.0 DOM 2 CSS 2 module
Events 2.0 DOM 2 Events module
UIEvents 2.0 DOM 2 User-interface Events module
MutationEvents 2.0 DOM 2 Mutation Events module
HTMLEvents 2.0 DOM 2 HTML Events module
Range 2.0 DOM 2 Range module
Traversal 2.0 DOM 2 Traversal module

This method is essentially the same as isSupported, except that it's only concerned with whether a feature is supported by the DOM implementation, rather than whether it's supported for a specific node.

CAUTION: In practise, this method is no use at all

This method is not at all useful in practise, because its data cannot be trusted. It should only return true if a browser conforms to a particular module — and I reckon this should mean, supports it fully without issues — but what we mostly find is that it returns true if a browser implements a module at all, even if it's implemented only partially, or with bugs.

Ultimately, hasFeature tells us nothing about whether a particular feature of the DOM can actually be used, so to most intents and purposes it tells us nothing at all.

In fact I can't see how this method would ever be useful, even if browsers were honest about it. To return true and say you support something when you only partly support it is neither helpful nor true, yet to return false might suggest that you don't support it at all, which is equally unhelpful and untrue.

The best way to establish support for something is to use feature detection (coming soon!).

Return value

Returns true if the feature is supported by this implementation, otherwise false

Compatibility

Internet Explorer Firefox Safari Opera
5.5 6.0 7.0 1.5 2.0 3.0 1.3 2.0 3.0 9.0 9.5
Partial Full Full Full Full Full Full Full Full Full Full

In Internet Explorer 5.5 in HTML this method is not available because the implementation object itself is undefined.

: Notes on how this method returns in different browsers

The following notes are an overview of how this method returns in different browsers, but it isn't really a summary of support — the method works correctly, it's just that its data isn't necessarily reliable.

Both Opera and Safari return true for everything, even though they blatantly don't implement every module fully (and for Safari in some cases, barely at all).

Internet Explorer in HTML only returns true for DOM 1 HTML. Internet Explorer in XML only returns true for DOM 1 XML. This is close to being the truth, but not completely, since in both cases the modules are not fully supported by IE.

Firefox returns true for everything except DOM 2 Mutation events and DOM 2 Traversal. This reflects missing features in those modules, and so it's the most honest of any browser, but it still doesn't tell the whole story given that other modules have bugs in their implementation.

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