HTML

Living Standard — Last Updated 24 September 2023

1. 2.6 Common DOM interfaces

2.6 Common DOM interfaces

2.6.1 Reflecting content attributes in IDL attributes

The building blocks for reflecting are as follows:

A reflected target is an element or ElementInternals object. It is typically clear from context and typically identical to the interface of the reflected IDL attribute. It is always identical to that interface when it is an ElementInternals object.
A reflected IDL attribute is an attribute interface member.
A reflected content attribute name is a string. When the reflected target is an element, it represents the local name of a content attribute whose namespace is null. When the reflected target is an ElementInternals object, it represents a key of the reflected target's target element's internal content attribute map.

A reflected IDL attribute can be defined to reflect a reflected content attribute name of a reflected target. In general this means that the IDL attribute getter returns the current value of the content attribute, and the setter changes the value of the content attribute to the given value.

If the reflected target is an element, then the reflected IDL attribute can additionally declare to support ElementInternals. This means that the ElementInternals interface also has a reflected IDL attribute, with the same identifier, and that reflected IDL attribute reflects the same reflected content attribute name.

The fooBar IDL attribute must reflect the foobar content attribute and support ElementInternals.

Reflected targets have these associated algorithms:

get the element: takes no arguments; returns an element.
get the content attribute: takes no arguments; returns null or a string.
set the content attribute: takes a string value; returns nothing.
delete the content attribute: takes no arguments; returns nothing.

For a reflected target that is an element element, these are defined as follows:

get the element

Return element.

get the content attribute

Let attribute be the result of running get an attribute by namespace and local name given null, the reflected content attribute name, and element.
If attribute is null, then return null.
Return attribute's value.

set the content attribute with a string value

Set an attribute value given element, the reflected content attribute name, and value.

delete the content attribute

Remove an attribute by namespace and local name given null, the reflected content attribute name, and element.

For a reflected target that is an ElementInternals object elementInternals, they are defined as follows:

get the element

Return elementInternals's target element.

get the content attribute

If elementInternals's target element's internal content attribute map[the reflected content attribute name] does not exist, then return null.
Return elementInternals's target element's internal content attribute map[the reflected content attribute name].

set the content attribute with a string value

Set elementInternals's target element's internal content attribute map[the reflected content attribute name] to value.

delete the content attribute

Remove elementInternals's target element's internal content attribute map[the reflected content attribute name].

This results in somewhat redundant data structures for ElementInternals objects as their target element's internal content attribute map cannot be directly manipulated and as such reflection is only happening in a single direction. This approach was nevertheless chosen to make it less error-prone to define IDL attributes that are shared between reflected targets and benefit from common API semantics.

IDL attributes of type DOMString? that reflect enumerated content attributes can be limited to only known values. Per the processing models below, those will cause the getters for such IDL attributes to only return keywords for those enumerated attributes, or the empty string or null.

If a reflected IDL attribute has the type


The getter steps are:
Let element be the result of running this's get the
element.
Let contentAttributeValue be the result of running this's
get the content attribute.
Let attributeDefinition be the attribute definition of element's
content attribute whose namespace is null and local name is the reflected content
attribute name.

If attributeDefinition indicates it is an enumerated attribute and
the reflected IDL attribute is defined to be limited to only known
values:
If contentAttributeValue does not correspond to any state of
attributeDefinition (e.g., it is null and there is no missing value default), or that it is in a state of
attributeDefinition with no associated keyword value, then return the empty
string.
Return the canonical keyword for the state of
attributeDefinition that contentAttributeValue corresponds to.
If contentAttributeValue is null, then return the empty string.
Return contentAttributeValue.

The setter steps are to run this's set the content attribute with the given value.

If a reflected IDL attribute has the type DOMString?:



The getter steps are:
Let element be the result of running this's get the
element.
Let contentAttributeValue be the result of running this's
get the content attribute.
Let attributeDefinition be the attribute definition of element's
content attribute whose namespace is null and local name is the reflected content
attribute name.
Assert: attributeDefinition indicates it is an enumerated
attribute.
Assert: the reflected IDL attribute is limited to only
known values.
Assert: contentAttributeValue corresponds to a state of
attributeDefinition.
If contentAttributeValue corresponds to a state of
attributeDefinition with no associated keyword value, then return null.
Return the canonical keyword for the state of
attributeDefinition that contentAttributeValue corresponds to.

The setter steps are:
If the given value is null, then run this's delete the content
attribute.
Otherwise, run this's set the content attribute with the given
value.

If a reflected IDL attribute has the type


The getter steps are:
Let element be the result of running this's get the
element.
Let contentAttributeValue be the result of running this's
get the content attribute.
Let attributeDefinition be the attribute definition of element's
content attribute whose namespace is null and local name is the reflected content
attribute name.

If attributeDefinition indicates it contains a URL:
If contentAttributeValue is null, then return the empty string.
Let urlString be the result of encoding-parsing-and-serializing a
URL given contentAttributeValue, relative to element's
node document.
If urlString is not failure, then return urlString.
Return contentAttributeValue, converted to a scalar value string.

The setter steps are to run this's set the content attribute with the given value.

If a reflected IDL attribute has the type


The getter steps are:
Let contentAttributeValue be the result of running this's
get the content attribute.
If contentAttributeValue is null, then return false.
Return true.


The setter steps are:
If the given value is false, then run this's delete the content
attribute.
If the given value is true, then run this's set the content
attribute with the empty string.


This corresponds to the rules for boolean content
attributes.
If a reflected IDL attribute has the type limited to only non-negative numbers and optionally with a default
value defaultValue:

The getter steps are:
Let contentAttributeValue be the result of running this's
get the content attribute.

If contentAttributeValue is not null:
Let parsedValue be the result of integer parsing contentAttributeValue if the reflected IDL
attribute is not limited to only non-negative numbers; otherwise the
result of non-negative integer
parsing contentAttributeValue.
If parsedValue is not an error and is within the parsedValue.

If the reflected IDL attribute has a default value, then
return defaultValue.
If the reflected IDL attribute is limited to only non-negative
numbers, then return −1.
Return 0.


The setter steps are:
If the reflected IDL attribute is limited to only non-negative
numbers and the given value is negative, then throw an
"IndexSizeError" this's set the content attribute with the given value
converted to the shortest possible string representing the number as a valid
integer.


If a reflected IDL attribute has the type , optionally limited to only positive
numbers, limited to only positive
numbers with fallback, or clamped to the range [clampedMin,
clampedMax], and optionally with a default value defaultValue:

The getter steps are:
Let contentAttributeValue be the result of running this's
get the content attribute.
Let minimum be 0.
If the reflected IDL attribute is limited to only positive
numbers or limited to only positive numbers with fallback, then set
minimum to 1.
If the reflected IDL attribute is clamped to the range, then
set minimum to clampedMin.
Let maximum be 2147483647 if the reflected IDL attribute is not
clamped to the range; otherwise clampedMax.

If contentAttributeValue is not null:
Let parsedValue be the result of non-negative integer parsing
contentAttributeValue.
If parsedValue is not an error and is in the range minimum to
maximum, inclusive, then return parsedValue.

If parsedValue is not an error and the reflected IDL attribute is
clamped to the range:
If parsedValue is less than minimum, then return
minimum.
Return maximum.

If the reflected IDL attribute has a default value, then
return defaultValue.
Return minimum.

The setter steps are:
If the reflected IDL attribute is limited to only positive
numbers and the given value is 0, then throw an
"IndexSizeError" minimum be 0.
If the reflected IDL attribute is limited to only positive
numbers or limited to only positive numbers with fallback, then set
minimum to 1.
Let newValue be minimum.
If the reflected IDL attribute has a default value, then set
newValue to defaultValue.
If the given value is in the range minimum to 2147483647, inclusive,
then set newValue to it.
Run this's set the content attribute with newValue
converted to the shortest possible string representing the number as a valid non-negative
integer.

Clamped to the range has no effect on the setter steps.

If a reflected IDL attribute has the type limited to only positive numbers
and optionally with a default value defaultValue:

The getter steps are:
Let contentAttributeValue be the result of running this's
get the content attribute.

If contentAttributeValue is not null:
Let parsedValue be the result of floating-point number parsing
contentAttributeValue.
If parsedValue is not an error and is greater than 0, then return
parsedValue.
If parsedValue is not an error and the reflected IDL attribute
is not limited to only positive numbers, then return
parsedValue.
If the reflected IDL attribute has a default value, then
return defaultValue.
Return 0.

The setter steps are:
If the reflected IDL attribute is limited to only positive
numbers and the given value is not greater than 0, then return.
Run this's set the content attribute with the given value,
converted to the best representation of the number as a floating-point
number.

The values Infinity and Not-a-Number (NaN) values throw an exception on setting,
as defined in Web IDL. [WEBIDL]
If a reflected IDL attribute has the type this and associated attribute's local name is the reflected content
attribute name. Specification authors cannot use support
ElementInternals for IDL attributes of this type.

If a reflected IDL attribute has the type T?,
where T is either

Let attr be the reflected content attribute name.

Its reflected target has an explicitly set attr-element, which is a weak reference to an element or null. It is initially null.


Its reflected target has an attr-associated element. To compute the attr-associated
element for such a reflected target reflectedTarget:
Let element be the result of running reflectedTarget's get
the element.
Let contentAttributeValue be the result of running
reflectedTarget's get the content attribute.

If reflectedTarget's explicitly set attr-element is not
null:
If reflectedTarget's explicitly set attr-element is
a descendant of any of element's shadow-including ancestors, then return
reflectedTarget's explicitly set attr-element.
Return null.

Otherwise, if contentAttributeValue is not null, return the first element
candidate, in tree order, that meets the following criteria:
candidate's root is the same as element's
root,
candidate's ID is
contentAttributeValue, and
candidate implements T.
If no such element exists, then return null.
Return null.

The getter steps are to return this's attr-associated element.


The setter steps are:

If the given value is null, then:
Set this's explicitly set attr-element to
null.
Run this's delete the content attribute.
Return.
Run this's set the content attribute with the empty
string.
Set this's explicitly set attr-element to a weak
reference to the given value.


For element reflected targets only: the following
attribute change steps, given
element, localName, oldValue, value, and
namespace, are used to synchronize between the content attribute and the IDL
attribute:
If localName is not attr or namespace is not null, then
return.
Set element's explicitly set attr-element to
null.

Reflected IDL attributes of this
type are strongly encouraged to have their identifier end in "Element" for
consistency.
If a reflected IDL attribute has the type FrozenArray<T>?, where T is either

Let attr be the reflected content attribute name.
Its reflected target has an explicitly set
attr-elements, which is either a list of weak references to
elements or null. It is initially null.
Its reflected target has a cached attr-associated
elements, which is a FrozenArray<T>?. It is
initially null.

Its reflected target has an attr-associated elements. To compute the
attr-associated elements for such a reflected target
reflectedTarget:
Let elements be an empty list.
Let element be the result of running reflectedTarget's get
the element.

If reflectedTarget's explicitly set attr-elements is not
null:

For each attrElement in
reflectedTarget's explicitly set attr-elements:
If attrElement is not a descendant of any of
element's shadow-including
ancestors, then continue.
Append attrElement to
elements.


Otherwise:
Let contentAttributeValue be the result of running
reflectedTarget's get the content attribute.
If contentAttributeValue is null, then return null.
Let tokens be contentAttributeValue, split on ASCII whitespace.

For each id of tokens:

Let candidate be the first element, in tree order, that meets
the following criteria:
candidate's root is the same as element's
root,
candidate's ID is id, and
candidate implements T.
If no such element exists, then continue.
Append candidate to
elements.

Return elements.

The getter steps are:
Let elements be this's attr-associated
elements.
If the contents of elements is equal to the contents of this's
cached attr-associated elements, then return this's
cached attr-associated elements.
Let elementsAsFrozenArray be elements, converted to a FrozenArray<T>?.
Set this's cached attr-associated elements to
elementsAsFrozenArray.
Return elementsAsFrozenArray.
This extra caching layer is necessary to preserve the invariant that element.reflectedElements === element.reflectedElements.

The setter steps are:

If the given value is null:
Set this's explicitly set attr-elements to
null.
Run this's delete the content attribute.
Return.
Run this's set the content attribute with the empty
string.
Let elements be an empty list.

For each element in the given value:
Append a weak reference to element to
elements.
Set this's explicitly set attr-elements to
elements.

For element reflected targets only: the following
attribute change steps, given
element, localName, oldValue, value, and
namespace, are used to synchronize between the content attribute and the IDL
attribute:
If localName is not attr or namespace is not null, then
return.
Set element's explicitly set attr-elements to
null.

Reflected IDL attributes of this
type are strongly encouraged to have their identifier end in "Elements" for
consistency.
2.6.2 Using reflect in specifications
Reflection is primarily about improving web developer ergonomics
by giving them typed access to content attributes through reflected IDL attributes. The ultimate source of truth, which the web platform
builds upon, is the content attributes themselves. That is, specification authors must not use the
reflected IDL attribute getter or setter steps, but instead must use the content
attribute presence and value. (Or an abstraction on top, such as the state of an enumerated
attribute.)
Two important exceptions to this are reflected IDL
attributes whose type is one of the following:
T?, where T is either T is either
For those, specification authors must use the reflected target's
attr-associated element and attr-associated
elements, respectively. The content attribute presence and value must not be used as they
cannot be fully synchronized with the reflected IDL attribute.

A reflected target's explicitly set attr-element,
explicitly set attr-elements, and cached attr-associated
elements are to be treated as internal implementation details and not to be built upon.
2.6.3 Collections
The HTMLFormControlsCollection and HTMLOptionsCollection interfaces
are collections derived from the
HTMLAllCollection interface is a collection, but is not so derived.
2.6.3.1 The HTMLAllCollection interface
The HTMLAllCollection interface is used for the legacy document.all attribute. It operates similarly to

All HTMLAllCollection objects are rooted at a Document
and have a filter that matches all elements, so the elements represented by the
collection of an HTMLAllCollection object consist of all the descendant
elements of the root Document.

Objects that implement the HTMLAllCollection interface are legacy platform objects with an additional [[Call]] internal
method described in the section below. They also have an
[[IsHTMLDDA]] internal slot.

Objects that implement the HTMLAllCollection interface have several unusual
behaviors, due of the fact that they have an [[IsHTMLDDA]] internal slot:
The ToBoolean abstract operation in JavaScript returns
false when given objects implementing the HTMLAllCollection interface.
The IsLooselyEqual abstract operation,
when given objects implementing the HTMLAllCollection interface, returns true when
compared to the undefined and null values.
(Comparisons using the IsStrictlyEqual abstract
operation, and IsLooselyEqual comparisons to other values such as strings or objects, are
unaffected.)
The typeof operator in JavaScript returns the string
"undefined" when applied to objects implementing the
HTMLAllCollection interface.
These special behaviors are motivated by a desire for compatibility with two classes of legacy
content: one that uses the presence of document.all as a
way to detect legacy user agents, and one that only supports those legacy user agents and uses
the document.all object without testing for its presence
first. [JAVASCRIPT]

[Exposed=Window,
 LegacyUnenumerableNamedProperties]
interface HTMLAllCollection {
  readonly attribute unsigned long length;
  getter Element (unsigned long index);
  getter (HTMLCollection or Element)? namedItem(DOMString name);
  (HTMLCollection or Element)? item(optional DOMString nameOrIndex);

  // Note: HTMLAllCollection objects have a custom [[Call]] internal method and an [[IsHTMLDDA]] internal slot.
};
The object's supported property indices are as defined for

The supported property names consist of the non-empty values of all the id attributes of all the elements represented by the
collection, and the non-empty values of all the name attributes of
all the "all"-named elements represented by the collection, in
tree order, ignoring later duplicates, with the id of
an element preceding its name if it contributes both, they differ from
each other, and neither is the duplicate of an earlier entry.

The length getter steps are to return the number
of nodes represented by the collection.
The indexed property getter must return the result of getting the "all"-indexed element from this
given the passed index.
The namedItem(name) method steps are
to return the result of getting the "all"-named
element(s) from this given name.
The item(nameOrIndex) method steps
are:
If nameOrIndex was not provided, return null.
Return the result of getting the
"all"-indexed or named element(s) from this, given
nameOrIndex.

The following elements are "all"-named elements:
a,
button,
embed,
form,
frame,
frameset,
iframe,
img,
input,
map,
meta,
object,
select, and
textarea

To get the "all"-indexed element from an
HTMLAllCollection collection given an index index, return the
index^th element in collection, or null if there is no such
index^th element.
To get the "all"-named element(s) from an
HTMLAllCollection collection given a name name, perform the
following steps:
If name is the empty string, return null.

Let subCollection be an Document as collection, whose filter matches only elements that are
either:
"all"-named elements with a name attribute equal to
name, or,
elements with an ID equal to name.
If there is exactly one element in subCollection, then return that
element.
Otherwise, if subCollection is empty, return null.
Otherwise, return subCollection.
To get the "all"-indexed or named
element(s) from an HTMLAllCollection collection given
nameOrIndex:
If nameOrIndex, converted to a
JavaScript String value, is an array index property name, return the result of getting the "all"-indexed element from
collection given the number represented by nameOrIndex.
Return the result of getting the "all"-named
element(s) from collection given nameOrIndex.
2.6.3.1.1 [[Call]] ( thisArgument, argumentsList )
If argumentsList's size is zero, or if
argumentsList[0] is undefined, return null.
Let nameOrIndex be the result of converting argumentsList[0] to a result be the result of getting the "all"-indexed or named element(s)
from this HTMLAllCollection given nameOrIndex.
Return the result of converting
result to an ECMAScript value.

The thisArgument is ignored, and thus code such as Function.prototype.call.call(document.all, null, "x") will still search for
elements. (document.all.call does not exist, since document.all does not inherit from Function.prototype.)
2.6.3.2 The HTMLFormControlsCollection interface
The HTMLFormControlsCollection interface is used for
collections of listed
elements in form elements.
HTMLFormControlsCollection
Support in all current engines.
Firefox1+Safari4+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet ExplorerNo
Firefox Android?Safari iOS1+Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
RadioNodeList
Support in all current engines.
Firefox33+Safari7+Chrome21+
Opera?Edge79+
Edge (Legacy)12+Internet Explorer9+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?
[Exposed=Window]
interface HTMLFormControlsCollection : HTMLCollection {
  // inherits length and item()
  getter (RadioNodeList or Element)? namedItem(DOMString name); // shadows inherited namedItem()
};

[Exposed=Window]
interface RadioNodeList : NodeList {
  attribute DOMString value;
};
collection.length
Returns the number of elements in collection.
element = collection.item(index)
element = collection[index]
Returns the item at index index in collection. The items are sorted
in tree order.
element = collection.namedItem(name)HTMLFormControlsCollection/namedItem
Support in all current engines.
Firefox33+Safari4+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet ExplorerNo
Firefox Android?Safari iOS1+Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
radioNodeList = collection.namedItem(name)
element = collection[name]
radioNodeList = collection[name]

Returns the item with ID or name name from collection.
If there are multiple matching items, then a RadioNodeList object containing all
those elements is returned.
radioNodeList.value
Returns the value of the first checked radio button represented by
radioNodeList.
radioNodeList.value = value
Checks the first first radio button represented by radioNodeList that has value
value.
The object's supported property indices are as defined for

The supported property names consist of the non-empty values of all the id and name attributes of all the
elements represented by the collection, in tree order, ignoring later
duplicates, with the id of an element preceding its name if it contributes both, they differ from each other, and neither is the
duplicate of an earlier entry.

The namedItem(name) method
must act according to the following algorithm:
If name is the empty string, return null and stop the algorithm.
If, at the time the method is called, there is exactly one node in the collection that has
either an id attribute or a name
attribute equal to name, then return that node and stop the algorithm.
Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal
to name, then return null and stop the algorithm.
Otherwise, create a new RadioNodeList object representing a live
view of the HTMLFormControlsCollection object, further filtered so that the only
nodes in the RadioNodeList object are those that have either an id attribute or a name attribute equal
to name. The nodes in the RadioNodeList object must be sorted in
tree order.
Return that RadioNodeList object.

Members of the RadioNodeList interface inherited from the 
RadioNodeList/value
Support in all current engines.
Firefox33+Safari7+Chrome21+
Opera?Edge79+
Edge (Legacy)12+Internet Explorer9+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?
The value IDL attribute on the
RadioNodeList object, on getting, must return the value returned by running the
following steps:

Let element be the first element in tree order
represented by the RadioNodeList object that is an input element whose
type attribute is in the Radio Button state and whose checkedness is true. Otherwise, let it be null.
If element is null, return the empty string.
If element is an element with no value attribute, return the string "on".
Otherwise, return the value of element's value attribute.
On setting, the value IDL attribute must run the
following steps:
If the new value is the string "on": let element be the first element in tree order
represented by the RadioNodeList object that is an input element whose
type attribute is in the Radio Button state and whose value content attribute is either absent, or present and equal to the new value, if any. If no such element exists, then instead let element be null.
Otherwise: let element be the first element in tree order
represented by the RadioNodeList object that is an input element whose
type attribute is in the Radio Button state and whose value content attribute is present and equal to the new value, if
any. If no such element exists, then instead let element be null.
If element is not null, then set its checkedness to true.

2.6.3.3 The HTMLOptionsCollection interface
HTMLOptionsCollection
Support in all current engines.
Firefox1+Safari3+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer6+
Firefox Android?Safari iOS1+Chrome Android?WebView Android37+Samsung Internet?Opera Android12.1+
The HTMLOptionsCollection interface is used for collections of option elements. It is always
rooted on a select element and has attributes and methods that manipulate that
element's descendants.
[Exposed=Window]
interface HTMLOptionsCollection : HTMLCollection {
  // inherits item(), namedItem()
  [CEReactions] attribute unsigned long length; // shadows inherited length
  [CEReactions] setter undefined (unsigned long index, HTMLOptionElement? option);
  [CEReactions] undefined add((HTMLOptionElement or HTMLOptGroupElement) element, optional (HTMLElement or long)? before = null);
  [CEReactions] undefined remove(long index);
  attribute long selectedIndex;
};
collection.length
Returns the number of elements in collection.
collection.length = value

When set to a smaller number than the existing length, truncates the number of
option elements in the container corresponding to collection.
When set to a greater number than the existing length, if that number is less than or equal
to 100000, adds new blank option elements to the container corresponding to
collection.
element = collection.item(index)
element = collection[index]
Returns the item at index index in collection. The items are sorted
in tree order.
collection[index] = element

When index is a greater number than the number of items in collection,
adds new blank option elements in the corresponding container.
When set to null, removes the item at index index from collection.
When set to an option element, adds or replaces it at index index in
collection.
element = collection.namedItem(name)
element = collection[name]

Returns the item with ID or name name from collection.
If there are multiple matching items, then the first is returned.
collection.add(element[, before])

Inserts element before the node given by before.
The before argument can be a number, in which case element is inserted
before the item with that number, or an element from collection, in which case
element is inserted before that element.
If before is omitted, null, or a number out of range, then element will
be added at the end of the list.
Throws a "HierarchyRequestError" element is an ancestor of the element into which it is to be inserted.

collection.remove(index)
Removes the item with index index from collection.
collection.selectedIndex
Returns the index of the first selected item, if any, or −1 if there is no selected
item.
collection.selectedIndex = index
Changes the selection to the option element at index index in
collection.

The object's supported property indices are as defined for

The length getter steps are to return the
number of nodes represented by the collection.

The length setter steps are:
Let current be the number of nodes represented by the
collection.

If the given value is greater than current, then:
If the given value is greater than 100,000, then return.
Let n be value − current.
Append n new option elements with no attributes and no child
nodes to the select element on which this is rooted. Mutation events
must be fired as if a option
elements had been inserted.

If the given value is less than current, then:
Let n be current − value.
Remove the last n nodes in the collection from their parent nodes.

Setting length never removes
or adds any optgroup elements, and never adds new children to existing
optgroup elements (though it can remove children from them).
The supported property names consist of the non-empty values of all the id and name attributes of all the
elements represented by the collection, in tree order, ignoring later
duplicates, with the id of an element preceding its name if it contributes both, they differ from each other, and neither is
the duplicate of an earlier entry.
When the user agent is to set the value of a new
indexed property or set the value of an existing indexed property for a given
property index index to a new value value, it must run the following
algorithm:
If value is null, invoke the steps for the remove method with index as
the argument, and return.
Let length be the number of nodes represented by the
collection.
Let n be index minus length.
If n is greater than zero, then append a n-1 new option elements with no attributes and
no child nodes to the select element on which the HTMLOptionsCollection
is rooted.
If n is greater than or equal to zero, append value to the select
element. Otherwise, replace the indexth element in the collection by value.

The add(element, before)
method must act according to the following algorithm:
If element is an ancestor of the select element on which
the HTMLOptionsCollection is rooted, then throw a
"HierarchyRequestError" before is an element, but that element isn't a descendant of the
select element on which the HTMLOptionsCollection is rooted, then throw
a "NotFoundError" element and before are the same element, then
return.
If before is a node, then let reference be that
node. Otherwise, if before is an integer, and there is a beforeth node in the collection, let reference be that node.
Otherwise, let reference be null.
If reference is not null, let parent be the parent
node of reference. Otherwise, let parent be the
select element on which the HTMLOptionsCollection is rooted.
Pre-insert element into parent node before
reference.


The remove(index) method must act
according to the following algorithm:
If the number of nodes represented by the collection is zero, return.
If index is not a number greater than or equal to 0 and less than the
number of nodes represented by the collection, return.
Let element be the indexth element in the
collection.
Remove element from its parent node.
The selectedIndex IDL attribute must act
like the identically named attribute on the select element on which the
HTMLOptionsCollection is rooted
2.6.4 The DOMStringList interface
DOMStringList
Support in all current engines.
Firefox1+Safari5.1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer10+
Firefox Android?Safari iOS?Chrome Android?WebView Android3+Samsung Internet?Opera Android12.1+
The DOMStringList interface is a non-fashionable retro way of representing a list
of strings.
[Exposed=(Window,Worker)]
interface DOMStringList {
  readonly attribute unsigned long length;
  getter DOMString? item(unsigned long index);
  boolean contains(DOMString string);
};
New APIs must use sequence<DOMString> or
equivalent rather than DOMStringList.
strings.length
Returns the number of strings in strings.
strings[index]
strings.item(index)
Returns the string with index index from strings.
strings.contains(string)
Returns true if strings contains string, and false
otherwise.
Each DOMStringList object has an associated list.
The DOMStringList interface supports indexed properties. The
supported property indices are the indices of this's
associated list.
DOMStringList/length
Support in all current engines.
Firefox1+Safari5.1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer10+
Firefox Android?Safari iOS?Chrome Android?WebView Android37+Samsung Internet?Opera Android12.1+
The length getter steps are to return
this's associated list's size.
DOMStringList/item
Support in all current engines.
Firefox1+Safari5.1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer10+
Firefox Android?Safari iOS?Chrome Android?WebView Android3+Samsung Internet?Opera Android12.1+
The item(index) method steps are to
return the indexth item in this's associated list, or null if
index plus one is greater than this's associated list's size.
DOMStringList/contains
Support in all current engines.
Firefox1.5+Safari5.1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer10+
Firefox Android?Safari iOS?Chrome Android?WebView Android3+Samsung Internet?Opera Android12.1+
The contains(string) method steps
are to return true if this's associated list contains string, and false otherwise.
← 2.4 URLs — Table of Contents — 2.7 Safe passing of structured data →

HTML

2.6 Common DOM interfaces

2.6.1 Reflecting content attributes in IDL attributes

2.6.2 Using reflect in specifications

2.6.3 Collections

2.6.3.1 The `HTMLAllCollection` interface

2.6.3.1.1 [[Call]] ( `thisArgument`, `argumentsList` )

2.6.3.2 The `HTMLFormControlsCollection` interface

2.6.3.3 The `HTMLOptionsCollection` interface

2.6.4 The `DOMStringList` interface