search
element with form functionality — Last Updated 1 December 2021CustomElementRegistry
interfaceSupport in all current engines.
Custom elements provide a way for authors to build their own fully-featured DOM elements. Although authors could always use non-standard elements in their documents, with application-specific behavior added after the fact by scripting or similar, such elements have historically been non-conforming and not very functional. By defining a custom element, authors can inform the parser how to properly construct an element and how elements of that class should react to changes.
Custom elements are part of a larger effort to "rationalise the platform", by explaining existing platform features (like the elements of HTML) in terms of lower-level author-exposed extensibility points (like custom element definition). Although today there are many limitations on the capabilities of custom elements—both functionally and semantically—that prevent them from fully explaining the behaviors of HTML's existing elements, we hope to shrink this gap over time.
For the purposes of illustrating how to create an autonomous custom element, let's define a custom element that encapsulates rendering a small icon for a country flag. Our goal is to be able to use it like so:
< flag-icon country = "nl" ></ flag-icon >
To do this, we first declare a class for the custom element, extending
HTMLElement
:
class FlagIcon extends HTMLElement {
constructor() {
super ();
this . _countryCode = null ;
}
static observedAttributes = [ "country" ];
attributeChangedCallback( name, oldValue, newValue) {
// name will always be "country" due to observedAttributes
this . _countryCode = newValue;
this . _updateRendering();
}
connectedCallback() {
this . _updateRendering();
}
get country() {
return this . _countryCode;
}
set country( v) {
this . setAttribute( "country" , v);
}
_updateRendering() {
// Left as an exercise for the reader. But, you'll probably want to
// check this.ownerDocument.defaultView to see if we've been
// inserted into a document with a browsing context, and avoid
// doing any work if not.
}
}
We then need to use this class to define the element:
customElements. define( "flag-icon" , FlagIcon);
At this point, our above code will work! The parser, whenever it sees the flag-icon
tag, will construct a new instance of our FlagIcon
class, and tell our code about its new country
attribute, which we then use to set the element's internal state and update its rendering (when
appropriate).
You can also create flag-icon
elements using the DOM API:
const flagIcon = document. createElement( "flag-icon" )
flagIcon. country = "jp"
document. body. appendChild( flagIcon)
Finally, we can also use the custom element constructor itself. That is, the above code is equivalent to:
const flagIcon = new FlagIcon()
flagIcon. country = "jp"
document. body. appendChild( flagIcon)
In this section form
refers to either a form
or a search
element.
Adding a static formAssociated
property, with a true value, makes an
autonomous custom element a form-associated custom element. The
ElementInternals
interface helps you to implement functions and properties common
to form control elements.
class MyCheckbox extends HTMLElement {
static formAssociated = true ;
static observedAttributes = [ 'checked' ];
constructor() {
super ();
this . _internals = this . attachInternals();
this . addEventListener( 'click' , this . _onClick. bind( this ));
}
get form() { return this . _internals. form; }
get name() { return this . getAttribute( 'name' ); }
get type() { return this . localName; }
get checked() { return this . hasAttribute( 'checked' ); }
set checked( flag) { this . toggleAttribute( 'checked' , Boolean( flag)); }
attributeChangedCallback( name, oldValue, newValue) {
// name will always be "checked" due to observedAttributes
this . _internals. setFormValue( this . checked ? 'on' : null );
}
_onClick( event) {
this . checked = ! this . checked;
}
}
customElements. define( 'my-checkbox' , MyCheckbox);
You can use the custom element my-checkbox
like a built-in
form-associated element. For example, putting it in form
or label
associates the my-checkbox
element with them, and submitting the
form
will send data provided by my-checkbox
implementation.
< form action = "..." method = "..." >
< label >< my-checkbox name = "agreed" ></ my-checkbox > I read the agreement.</ label >
< input type = "submit" >
</ form >
By using the appropriate properties of ElementInternals
, your custom element can
have default accessibility semantics. The following code expands our form-associated checkbox from
the previous section to properly set its default role and checkedness, as viewed by accessibility
technology:
class MyCheckbox extends HTMLElement {
static formAssociated = true ;
static observedAttributes = [ 'checked' ];
constructor() {
super ();
this . _internals = this . attachInternals();
this . addEventListener( 'click' , this . _onClick. bind( this ));
this . _internals. role = 'checkbox' ;
this . _internals. ariaChecked = false ;
}
get form() { return this . _internals. form; }
get name() { return this . getAttribute( 'name' ); }
get type() { return this . localName; }
get checked() { return this . getAttribute( 'checked' ); }
set checked( flag) { this . toggleAttribute( 'checked' , Boolean( flag)); }
attributeChangedCallback( name, oldValue, newValue) {
// name will always be "checked" due to observedAttributes
this . _internals. setFormValue( this . checked ? 'on' : null );
this . _internals. ariaChecked = this . checked;
}
_onClick( event) {
this . checked = ! this . checked;
}
}
customElements. define( 'my-checkbox' , MyCheckbox);
Note that, like for built-in elements, these are only defaults, and can be overridden by the
page author using the role
and aria-*
attributes:
<!-- This markup is non-conforming -->
< input type = "checkbox" checked role = "button" aria-checked = "false" >
<!-- This markup is probably not what the custom element author intended -->
< my-checkbox role = "button" checked aria-checked = "false" >
Custom element authors are encouraged to state what aspects of their accessibility semantics
are strong native semantics, i.e., should not be overridden by users of the custom element. In our
example, the author of the my-checkbox
element would state that its
role and aria-checked
values are strong
native semantics, thus discouraging code such as the above.
Customized built-in elements are a distinct kind of custom element, which are defined slightly differently and used very differently compared to autonomous custom elements. They exist to allow reuse of behaviors from the existing elements of HTML, by extending those elements with new custom functionality. This is important since many of the existing behaviors of HTML elements can unfortunately not be duplicated by using purely autonomous custom elements. Instead, customized built-in elements allow the installation of custom construction behavior, lifecycle hooks, and prototype chain onto existing elements, essentially "mixing in" these capabilities on top of the already-existing element.
Customized built-in elements require a distinct syntax from autonomous custom elements because user agents and other software key off an element's local name in order to identify the element's semantics and behavior. That is, the concept of customized built-in elements building on top of existing behavior depends crucially on the extended elements retaining their original local name.
In this example, we'll be creating a customized built-in element named plastic-button
, which behaves like a normal button but gets fancy animation
effects added whenever you click on it. We start by defining a class, just like before, although
this time we extend HTMLButtonElement
instead of HTMLElement
:
class PlasticButton extends HTMLButtonElement {
constructor() {
super ();
this . addEventListener( "click" , () => {
// Draw some fancy animation effects!
});
}
}
When defining our custom element, we have to also specify the extends
option:
customElements. define( "plastic-button" , PlasticButton, { extends : "button" });
In general, the name of the element being extended cannot be determined simply by looking at
what element interface it extends, as many elements share the same interface (such as
q
and blockquote
both sharing HTMLQuoteElement
).
To construct our customized built-in element from parsed HTML source text, we use
the is
attribute on a button
element:
< button is = "plastic-button" > Click Me!</ button >
Trying to use a customized built-in element as an autonomous custom
element will not work; that is, <plastic-button>Click
me?</plastic-button>
will simply create an HTMLElement
with no special
behavior.
If you need to create a customized built-in element programmatically, you can use the following
form of createElement()
:
const plasticButton = document. createElement( "button" , { is: "plastic-button" });
plasticButton. textContent = "Click me!" ;
And as before, the constructor will also work:
const plasticButton2 = new PlasticButton();
console. log( plasticButton2. localName); // will output "button"
console. assert( plasticButton2 instanceof PlasticButton);
console. assert( plasticButton2 instanceof HTMLButtonElement);
Note that when creating a customized built-in element programmatically, the is
attribute will not be present in the DOM, since it was not explicitly
set. However, it will be added to the output when
serializing:
console. assert( ! plasticButton. hasAttribute( "is" ));
console. log( plasticButton. outerHTML); // will output '<button is="plastic-button"></button>'
Regardless of how it is created, all of the ways in which button
is special
apply to such "plastic buttons" as well: their focus behavior, ability to participate in form submission, the disabled
attribute, and so on.
Customized built-in elements are designed to allow extension of existing HTML
elements that have useful user-agent supplied behavior or APIs. As such, they can only extend
existing HTML elements defined in this specification, and cannot extend legacy elements such as
bgsound
, blink
, isindex
, keygen
,
multicol
, nextid
, or spacer
that have been defined to use
HTMLUnknownElement
as their element interface.
One reason for this requirement is future-compatibility: if a customized built-in
element was defined that extended a currently-unknown element, for example combobox
, this would prevent this specification from defining a combobox
element in the future, as consumers of the derived customized
built-in element would have come to depend on their base element having no interesting
user-agent-supplied behavior.
As specified below, and alluded to above, simply defining and using an element called
taco-button
does not mean that such elements represent buttons. That is, tools such as web browsers, search engines,
or accessibility technology will not automatically treat the resulting element as a button just
based on its defined name.
To convey the desired button semantics to a variety of users, while still using an autonomous custom element, a number of techniques would need to be employed:
The addition of the tabindex
attribute would make the
taco-button
focusable. Note that if the
taco-button
were to become logically disabled, the tabindex
attribute would need to be removed.
The addition of an ARIA role and various ARIA states and properties helps convey semantics
to accessibility technology. For example, setting the role to "button
" will convey the semantics that this is a button,
enabling users to successfully interact with the control using usual button-like interactions in
their accessibility technology. Setting the aria-label
property is necessary to give the button an accessible
name, instead of having accessibility technology traverse its child text nodes and
announce them. And setting the aria-disabled
state to
"true
" when the button is logically disabled conveys to accessibility
technology the button's disabled state.
The addition of event handlers to handle commonly-expected button behaviors helps convey
the semantics of the button to web browser users. In this case, the most relevant event handler
would be one that proxies appropriate keydown
events to
become click
events, so that you can activate the button both
with keyboard and by clicking.
In addition to any default visual styling provided for taco-button
elements, the visual styling will also need to be updated to reflect changes in logical state,
such as becoming disabled; that is, whatever style sheet has rules for taco-button
will also need to have rules for taco-button[disabled]
.
With these points in mind, a full-featured taco-button
that took on the
responsibility of conveying button semantics (including the ability to be disabled) might look
something like this:
class TacoButton extends HTMLElement {
static observedAttributes = [ "disabled" ];
constructor() {
super ();
this . _internals = this . attachInternals();
this . _internals. role = "button" ;
this . addEventListener( "keydown" , e => {
if ( e. code === "Enter" || e. code === "Space" ) {
this . dispatchEvent( new PointerEvent( "click" , {
bubbles: true ,
cancelable: true
}));
}
});
this . addEventListener( "click" , e => {
if ( this . disabled) {
e. preventDefault();
e. stopImmediatePropagation();
}
});
this . _observer = new MutationObserver(() => {
this . _internals. ariaLabel = this . textContent;
});
}
connectedCallback() {
this . setAttribute( "tabindex" , "0" );
this . _observer. observe( this , {
childList: true ,
characterData: true ,
subtree: true
});
}
disconnectedCallback() {
this . _observer. disconnect();
}
get disabled() {
return this . hasAttribute( "disabled" );
}
set disabled( flag) {
this . toggleAttribute( "disabled" , Boolean( flag));
}
attributeChangedCallback( name, oldValue, newValue) {
// name will always be "disabled" due to observedAttributes
if ( this . disabled) {
this . removeAttribute( "tabindex" );
this . _internals. ariaDisabled = "true" ;
} else {
this . setAttribute( "tabindex" , "0" );
this . _internals. ariaDisabled = "false" ;
}
}
}
Even with this rather-complicated element definition, the element is not a pleasure to use for
consumers: it will be continually "sprouting" tabindex
attributes of its own volition, and its choice of tabindex="0"
focusability
behavior may not match the button
behavior on the current platform. This is because
as of now there is no way to specify default focus behavior for custom elements, forcing the use
of the tabindex
attribute to do so (even though it is usually
reserved for allowing the consumer to override default behavior).
In contrast, a simple customized built-in element, as shown in the previous
section, would automatically inherit the semantics and behavior of the button
element, with no need to implement these behaviors manually. In general, for any elements with
nontrivial behavior and semantics that build on top of existing elements of HTML, customized built-in elements will be easier to
develop, maintain, and consume.
Because element definition can occur at any time, a non-custom element could be created, and then later become a custom element after an appropriate definition is registered. We call this process "upgrading" the element, from a normal element into a custom element.
Upgrades enable scenarios where it may be
preferable for custom element definitions to be
registered after relevant elements have been initially created, such as by the parser. They allow
progressive enhancement of the content in the custom element. For example, in the following HTML
document the element definition for img-viewer
is loaded
asynchronously:
<!DOCTYPE html>
< html lang = "en" >
< title > Image viewer example</ title >
< img-viewer filter = "Kelvin" >
< img src = "images/tree.jpg" alt = "A beautiful tree towering over an empty savannah" >
</ img-viewer >
< script src = "js/elements/img-viewer.js" async ></ script >
The definition for the img-viewer
element here is loaded using a
script
element marked with the async
attribute, placed after the <img-viewer>
tag in the markup. While the
script is loading, the img-viewer
element will be treated as an undefined
element, similar to a span
. Once the script loads, it will define the img-viewer
element, and the existing img-viewer
element on
the page will be upgraded, applying the custom element's definition (which presumably includes
applying an image filter identified by the string "Kelvin", enhancing the image's visual
appearance).
Note that upgrades only apply to elements in the document tree. (Formally, elements that are connected.) An element that is not inserted into a document will stay un-upgraded. An example illustrates this point:
<!DOCTYPE html>
< html lang = "en" >
< title > Upgrade edge-cases example</ title >
< example-element ></ example-element >
< script >
"use strict" ;
const inDocument = document. querySelector( "example-element" );
const outOfDocument = document. createElement( "example-element" );
// Before the element definition, both are HTMLElement:
console. assert( inDocument instanceof HTMLElement);
console. assert( outOfDocument instanceof HTMLElement);
class ExampleElement extends HTMLElement {}
customElements. define( "example-element" , ExampleElement);
// After element definition, the in-document element was upgraded:
console. assert( inDocument instanceof ExampleElement);
console. assert( ! ( outOfDocument instanceof ExampleElement));
document. body. appendChild( outOfDocument);
// Now that we've moved the element into the document, it too was upgraded:
console. assert( outOfDocument instanceof ExampleElement);
</ script >
When authoring custom element constructors, authors are bound by the following conformance requirements:
A parameter-less call to super()
must be the first statement in the
constructor body, to establish the correct prototype chain and this value before any
further code is run.
A return
statement must not appear anywhere inside the constructor
body, unless it is a simple early-return (return
or return
this
).
The constructor must not use the document.write()
or document.open()
methods.
The element's attributes and children must not be inspected, as in the non-upgrade case none will be present, and relying on upgrades makes the element less usable.
The element must not gain any attributes or children, as this violates the expectations of
consumers who use the createElement
or createElementNS
methods.
In general, work should be deferred to connectedCallback
as much as
possible—especially work involving fetching resources or rendering. However, note that connectedCallback
can be called more than once, so any initialization work that
is truly one-time will need a guard to prevent it from running twice.
In general, the constructor should be used to set up initial state and default values, and to set up event listeners and possibly a shadow root.
Several of these requirements are checked during element creation, either directly or indirectly, and failing to follow them will result in a custom element that cannot be instantiated by the parser or DOM APIs. This is true even if the work is done inside a constructor-initiated microtask, as a microtask checkpoint can occur immediately after construction.
When authoring custom element reactions, authors should avoid manipulating the node tree as this can lead to unexpected results.
An element's connectedCallback
can be queued before the element is
disconnected, but as the callback queue is still processed, it results in a connectedCallback
for an element that is no longer connected:
class CParent extends HTMLElement {
connectedCallback() {
this . firstChild. remove();
}
}
customElements. define( "c-parent" , CParent);
class CChild extends HTMLElement {
connectedCallback() {
console. log( "CChild connectedCallback: isConnected =" , this . isConnected);
}
}
customElements. define( "c-child" , CChild);
const parent = new CParent(),
child = new CChild();
parent. append( child);
document. body. append( parent);
// Logs:
// CChild connectedCallback: isConnected = false
A custom element is an element that is custom. Informally, this means that its constructor and prototype are defined by the author, instead of by the user agent. This author-supplied constructor function is called the custom element constructor.
Two distinct types of custom elements can be defined:
An autonomous custom element, which is defined with no extends
option. These types of custom elements have a local name equal to their
defined name.
A customized built-in element, which is defined with an extends
option. These types of custom elements have a local name equal to the
value passed in their extends
option, and their defined name is used as the value of the
is
attribute, which
therefore must be a valid custom element name.
After a custom element is created,
changing the value of the is
attribute does not
change the element's behavior.
Autonomous custom elements have the following element definition:
is
attributeform
, for form-associated custom elements — Associates the element with a formdisabled
, for form-associated custom elements — Whether the form control is disabledreadonly
, for form-associated custom elements — Affects willValidate
, plus any behavior added by the custom element authorname
, for form-associated custom elements — Name of the element to use for form submission and in the form.elements
API HTMLElement
)An autonomous custom element does not have any special meaning: it represents its children. A customized built-in element inherits the semantics of the element that it extends.
Any namespace-less attribute that is relevant to the element's functioning, as determined by
the element's author, may be specified on an autonomous custom element, so long as
the attribute name is XML-compatible and contains no ASCII upper alphas. The exception is the is
attribute,
which must not be specified on an autonomous custom element (and which will have no
effect if it is).
Customized built-in elements follow the
normal requirements for attributes, based on the elements they extend. To add custom
attribute-based behavior, use data-*
attributes.
An autonomous custom element is called a form-associated custom element if the element is associated with a custom element definition whose form-associated field is set to true.
The name
attribute represents the form-associated
custom element's name. The disabled
attribute is
used to make the form-associated custom element non-interactive and to prevent its
submission value from being submitted. The form
attribute is used to explicitly associate the
form-associated custom element with its form owner.
The readonly
attribute of form-associated custom elements specifies that the element is barred
from constraint validation. User agents don't provide any other behavior for the attribute,
but custom element authors should, where possible, use its presence to make their control
non-editable in some appropriate fashion, similar to the behavior for the readonly attribute on built-in form controls.
Constraint validation: If the readonly
attribute is specified on a form-associated
custom element, the element is barred from constraint validation.
The reset algorithm for form-associated custom elements is to enqueue
a custom element callback reaction with the element, callback name "formResetCallback
", and an empty argument list.
A valid custom element name is a sequence of characters name that meets all of the following requirements:
name must match the PotentialCustomElementName
production:
PotentialCustomElementName ::=
[a-z] (PCENChar)* '-'
(PCENChar)*
PCENChar ::=
"-" | "." | [0-9] | "_" | [a-z] | #xB7 | [#xC0-#xD6] | [#xD8-#xF6] |
[#xF8-#x37D] | [#x37F-#x1FFF] | [#x200C-#x200D] | [#x203F-#x2040] | [#x2070-#x218F] |
[#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] |
[#x10000-#xEFFFF]
This uses the EBNF notation from the XML specification. [XML]
name must not be any of the following:
annotation-xml
color-profile
font-face
font-face-src
font-face-uri
font-face-format
font-face-name
missing-glyph
The list of names above is the summary of all hyphen-containing element names from the applicable specifications, namely SVG 2 and MathML. [SVG] [MATHML]
These requirements ensure a number of goals for valid custom element names:
They start with an ASCII lower alpha, ensuring that the HTML parser will treat them as tags instead of as text.
They do not contain any ASCII upper alphas, ensuring that the user agent can always treat HTML elements ASCII-case-insensitively.
They contain a hyphen, used for namespacing and to ensure forward compatibility (since no elements will be added to HTML, SVG, or MathML with hyphen-containing local names in the future).
They can always be created with createElement()
and createElementNS()
, which have restrictions that go
beyond the parser's.
Apart from these restrictions, a large variety of names is allowed, to give maximum
flexibility for use cases like <math-α>
or <emotion-😍>
.
CustomElementRegistry
interfaceSupport in all current engines.
Custom element registries are associated with Window
objects, instead
of Document
objects, since each custom element constructor inherits from
the HTMLElement
interface, and there is exactly one HTMLElement
interface per Window
object.
window.customElements.define(name,
constructor)
window.customElements.define(name, constructor,
{ extends: baseLocalName })
NotSupportedError
"
DOMException
will be thrown upon trying to extend a custom element or
an unknown element.window.customElements.get(name)
window.customElements.whenDefined(name)
SyntaxError
" DOMException
if not
given a valid custom element name.window.customElements.upgrade(root)
Element definition is a process of adding a custom element definition
to the CustomElementRegistry
. This is accomplished by the define()
method.
The whenDefined()
method can be
used to avoid performing an action until all appropriate custom
elements are defined. In this example, we
combine it with the :defined
pseudo-class to hide a
dynamically-loaded article's contents until we're sure that all of the autonomous custom elements it uses are defined.
articleContainer. hidden = true ;
fetch( articleURL)
. then( response => response. text())
. then( text => {
articleContainer. innerHTML = text;
return Promise. all(
[... articleContainer. querySelectorAll( ":not(:defined)" )]
. map( el => customElements. whenDefined( el. localName))
);
})
. then(() => {
articleContainer. hidden = false ;
});
The upgrade()
method allows upgrading
of elements at will. Normally elements are automatically upgraded when they become
connected, but this method can be used if you need to upgrade before you're ready to
connect the element.
const el = document. createElement( "spider-man" );
class SpiderMan extends HTMLElement {}
customElements. define( "spider-man" , SpiderMan);
console. assert( ! ( el instanceof SpiderMan)); // not yet upgraded
customElements. upgrade( el);
console. assert( el instanceof SpiderMan); // upgraded!
A custom element possesses the ability to respond to certain occurrences by running author code:
When upgraded, its constructor is run, with no arguments.
When it becomes connected, its connectedCallback
is
called, with no arguments.
When it becomes disconnected, its disconnectedCallback
is called, with no arguments.
When it is adopted into a new document, its adoptedCallback
is called, given the old document and new document as
arguments.
When any of its attributes are changed, appended, removed, or replaced, its attributeChangedCallback
is called, given the attribute's local name, old value,
new value, and namespace as arguments. (An attribute's old or new value is considered to be null
when the attribute is added or removed, respectively.)
When the user agent resets the form owner of a
form-associated custom element and doing so changes the form owner, its formAssociatedCallback
is called, given the new form owner (or null if no owner)
as an argument.
When the form owner of a form-associated custom element is reset, its formResetCallback
is
called.
When the disabled state of a
form-associated custom element is changed, its formDisabledCallback
is called, given the new state as an
argument.
When user agent updates a form-associated custom element's value on behalf of
a user or as part of navigation, its formStateRestoreCallback
is called, given the new value and a string indicating
a reason, "autocomplete
" or "restore
", as
arguments.
We call these reactions collectively custom element reactions.
The way in which custom element reactions are invoked is done with special care, to avoid running author code during the middle of delicate operations. Effectively, they are delayed until "just before returning to user script". This means that for most purposes they appear to execute synchronously, but in the case of complicated composite operations (like cloning, or range manipulation), they will instead be delayed until after all the relevant user agent processing steps have completed, and then run together as a batch.
It is guaranteed that custom element reactions always are invoked in the same order as their triggering actions, at least within the local context of a single custom element. (Because custom element reaction code can perform its own mutations, it is not possible to give a global ordering guarantee across multiple elements.)
Certain capabilities are meant to be available to a custom element author, but not to a custom
element consumer. These are provided by the element.attachInternals()
method, which returns an instance of
ElementInternals
. The properties and methods of ElementInternals
allow
control over internal features which the user agent provides to all elements.
element.attachInternals()
Returns an ElementInternals
object targeting the custom element
element. Throws an exception if element is not a custom
element, if the "internals
" feature was disabled as part of the
element definition, or if it is called twice on the same element.
internals.shadowRoot
Returns the ShadowRoot
for internals's target element, if the target
element is a shadow host, or null otherwise.
In this section form
refers to either a form
or a search
element.
internals.setFormValue(value)
Sets both the state and submission value of internals's target element to value.
If value is null, the element won't participate in form submission.
internals.setFormValue(value,
state)
Sets the submission value of internals's target element to value, and its state to state.
If value is null, the element won't participate in form submission.
internals.form
Returns the form owner of internals's target element.
internals.setValidity(flags,
message [, anchor ])
Marks internals's target element as
suffering from the constraints indicated by the flags argument, and sets the element's
validation message to message. If anchor is specified, the user agent might
use it to indicate problems with the constraints of internals's target element when the form owner is validated
interactively or reportValidity()
is
called.
internals.setValidity({})
Marks internals's target element as satisfying its constraints.
internals .
willValidate
Returns true if internals's target element will be validated when the form is submitted; false otherwise.
internals.validity
Returns the ValidityState
object for internals's target element.
internals .
validationMessage
Returns the error message that would be shown to the user if internals's target element was to be checked for validity.
valid = internals .
checkValidity()
Returns true if internals's target
element has no validity problems; false otherwise. Fires an invalid
event at the element in the latter case.
valid = internals .
reportValidity()
Returns true if internals's target
element has no validity problems; otherwise, returns false, fires an invalid
event at the element, and (if the event isn't canceled)
reports the problem to the user.
internals.labels
Returns a NodeList
of all the label
elements that
internals's target element is associated
with.
Each form-associated custom element has submission value. It is used to provide one or more
entries on form submission.
The initial value of submission value is null, and
submission value can be null, a string, a
File
, or a list of entries.
Each form-associated custom element has state.
It is information with which the user agent can restore a user's input for the element.
The initial value of state is null, and state can be null, a string, a File
, or a
list of entries.
The setFormValue()
method is used by
the custom element author to set the element's submission
value and state, thus communicating these to the user
agent.
When the user agent believes it is a good idea to restore a form-associated custom
element's state, for example after navigation or restarting the user agent, they may enqueue a
custom element callback reaction with that element, callback name "formStateRestoreCallback
", an argument list containing the state to be
restored, and "restore
".
If the user agent has a form-filling assist feature, then when the feature is invoked,
it may enqueue a custom element callback reaction with
a form-associated custom element, callback name
"formStateRestoreCallback
", an argument list containing the state value
determined by history of state value and some heuristics, and
"autocomplete
".
In general, the state is information specified by a user, and the submission value is a value after canonicalization or sanitization, suitable for submission to the server. The following examples makes this concrete:
Suppose that we have a form-associated custom element which asks a
user to specify a date. The user specifies "3/15/2019", but the control wishes to
submit "2019-03-15"
to the server. "3/15/2019" would be a state of the element, and "2019-03-15"
would be
a submission value.
Suppose you develop a custom element emulating a the behavior of the existing
checkbox input
type. Its submission value would be the value of its value
content attribute, or the string "on"
. Its state would be one of "checked"
, "unchecked"
, "checked/indeterminate"
, or "unchecked/indeterminate"
.
internals.role [ = value ]
Sets or retrieves the default ARIA role for internals's target element, which will be used unless the page author
overrides it using the role
attribute.
internals.aria* [ = value ]
Sets or retrieves various default ARIA states or property values for
internals's target element, which will be used
unless the page author overrides them using the aria-*
attributes.
By using the role
and aria*
properties of
ElementInternals
, custom element authors can set default accessibile roles, states,
and property values for their custom element, similar to how native elements behave. See the example above for more details.