HTML

Living Standard — Last Updated 30 November 2020

1. 1. 7.3 The Window object
      1. 7.3.1 APIs for creating and navigating browsing contexts by name
      2. 7.3.2 Accessing other browsing contexts
      3. 7.3.3 Named access on the Window object
      4. 7.3.4 Discarding browsing contexts
      5. 7.3.5 Closing browsing contexts
      6. 7.3.6 Browser interface elements
      7. 7.3.7 Script settings for Window objects
   2. 7.4 The WindowProxy exotic object
      1. 7.4.1 [[GetPrototypeOf]] ( )
      2. 7.4.2 [[SetPrototypeOf]] ( V )
      3. 7.4.3 [[IsExtensible]] ( )
      4. 7.4.4 [[PreventExtensions]] ( )
      5. 7.4.5 [[GetOwnProperty]] ( P )
      6. 7.4.6 [[DefineOwnProperty]] ( P , Desc )
      7. 7.4.7 [[Get]] ( P , Receiver )
      8. 7.4.8 [[Set]] ( P , V , Receiver )
      9. 7.4.9 [[Delete]] ( P )
      10. 7.4.10 [[OwnPropertyKeys]] ( )

7.3 The Window object

[Global=Window,
 Exposed=Window,
 LegacyUnenumerableNamedProperties]
interface Window : EventTarget {
  // the current browsing context
  [LegacyUnforgeable] readonly attribute WindowProxy window;
  [Replaceable] readonly attribute WindowProxy self;
  [LegacyUnforgeable] readonly attribute Document document;
  attribute DOMString name; 
  [PutForwards=href, LegacyUnforgeable] readonly attribute Location location;
  readonly attribute History history;
  readonly attribute CustomElementRegistry customElements;
  [Replaceable] readonly attribute BarProp locationbar;
  [Replaceable] readonly attribute BarProp menubar;
  [Replaceable] readonly attribute BarProp personalbar;
  [Replaceable] readonly attribute BarProp scrollbars;
  [Replaceable] readonly attribute BarProp statusbar;
  [Replaceable] readonly attribute BarProp toolbar;
  attribute DOMString status;
  undefined close();
  readonly attribute boolean closed;
  undefined stop();
  undefined focus();
  undefined blur();
  // other browsing contexts
  [Replaceable] readonly attribute WindowProxy frames;
  [Replaceable] readonly attribute unsigned long length;
  [LegacyUnforgeable] readonly attribute WindowProxy? top;
  attribute any opener;
  [Replaceable] readonly attribute WindowProxy? parent;
  readonly attribute Element? frameElement;
  WindowProxy? open(optional USVString url = "", optional DOMString target = "_blank", optional [LegacyNullToEmptyString] DOMString features = "");
  getter object (DOMString name);
  // Since this is the global object, the IDL named getter adds a NamedPropertiesObject exotic
  // object on the prototype chain. Indeed, this does not make the global object an exotic object.
  // Indexed access is taken care of by the WindowProxy exotic object.
  // the user agent
  readonly attribute Navigator navigator; 
  [SecureContext] readonly attribute ;

  readonly attribute boolean originIsolated;
  // user prompts
  undefined alert();
  undefined alert(DOMString message);
  boolean confirm(optional DOMString message = "");
  DOMString? prompt(optional DOMString message = "", optional DOMString default = "");
  undefined print();
  undefined postMessage(any message, USVString targetOrigin, optional sequence<object> transfer = []);
  undefined postMessage(any message, optional WindowPostMessageOptions options = {});
  // also has obsolete members
};
Window includes GlobalEventHandlers;
Window includes WindowEventHandlers;
dictionary WindowPostMessageOptions : PostMessageOptions {
  USVString targetOrigin = "/";
};

window . window

window . frames

window . self

These attributes all return window .

window . document

Returns the Document associated with window .

document . defaultView

Returns the Window object of the active document .

The Window object has an associated Document , which is a Document object. It is set when the Window object is created, and only ever changed during navigation from the initial about:blank Document .

The Window object's browsing context is the Window object's associated Document 's browsing context . It is either null or a browsing context .

The window , frames , and self attributes' getters must return this Window object's relevant Realm .[[GlobalEnv]]'s EnvironmentRecord 's [[GlobalThisValue]].

The document IDL attribute, on getting, must return this Window object's associated Document .

The Document object associated with a Window object can change in exactly one case: when the navigate algorithm creates a new Document object for the first page loaded in a browsing context . In that specific case, the Window object of the original about:blank page is reused and gets a new Document object.

The defaultView attribute's getter, when invoked, must run these steps:

1. If this Document object's browsing context is null, then return null.

2. Return this Document object's browsing context 's WindowProxy object.

For historical reasons, Window objects must also have a writable, configurable, non-enumerable property named HTMLDocument whose value is the Document interface object .

7.3.1 APIs for creating and navigating browsing contexts by name

window = window . open ( [ url [, target [, features ] ] ] )

Opens a window to show url (defaults to about:blank ), and returns it. The target argument gives the name of the new window. If a window exists with that name already, it is reused. The features argument can be used to influence the rendering of the new window.

window . name [ = value ]

Returns the name of the window.

Can be set, to change the name.

window . close ()

Closes the window.

window . closed

Returns true if the window has been closed, false otherwise.

window . stop ()

Cancels the document load.

The window open steps , given a string url , a string target , and a string features , are as follows:

1. If the event loop 's termination nesting level is nonzero, return null.

2. Let source browsing context be the entry global object 's browsing context .

3. If target is the empty string, then set target to " _blank ".

4. Let tokenizedFeatures be the result of tokenizing features .

5. Let noopener and noreferrer be false.

6. If tokenizedFeatures [" noopener "] exists , then:

   1. Set noopener to the result of parsing tokenizedFeatures [" noopener "] as a boolean feature .

   2. Remove tokenizedFeatures [" noopener "].

7. If tokenizedFeatures [" noreferrer "] exists , then:

   1. Set noreferrer to the result of parsing tokenizedFeatures [" noreferrer "] as a boolean feature .

   2. Remove tokenizedFeatures [" noreferrer "].

8. If noreferrer is true, then set noopener to true.

9. Let target browsing context and windowType be the result of applying the rules for choosing a browsing context given target , source browsing context , and noopener .

   If there is a user agent that supports control-clicking a link to open it in a new tab, and the user control-clicks on an element whose onclick handler uses the window.open() API to open a page in an iframe element, the user agent could override the selection of the target browsing context to instead target a new tab.

10. Let new be true if windowType is either " new and unrestricted " or " new with no opener ", and false otherwise.

11. If target browsing context is null, then return null.

12. If new is true, then set up browsing context features for target browsing context given tokenizedFeatures . [CSSOMVIEW]

13. Let urlRecord be the URL " about:blank ".

14. If url is not the empty string or new is true, then:

    1. If url is not the empty string, then parse url relative to the entry settings object , and set urlRecord to the resulting URL record , if any. If the parse a URL algorithm failed, then throw a " SyntaxError " DOMException .

    2. Let request be a new request whose URL is urlRecord .

    3. If noreferrer is true, then set request 's referrer to " noreferrer ".

    4. Let window be target browsing context 's active window .

    5. If urlRecord is " about:blank " and new is true, then queue a global task on the networking task source given window to fire an event named load at window , with the legacy target override flag set.

    6. Otherwise:

       1. Let historyHandling be " replace " if new is true; otherwise " default ".

       2. Navigate target browsing context to request , with exceptionsEnabled set to true, historyHandling set to historyHandling , and the source browsing context set to source browsing context .

15. If noopener is true or windowType is " new with no opener ", then return null.

16. Otherwise, if new is false, set target browsing context 's opener browsing context to source browsing context .

    If new is true this is done as part of creating a new auxiliary browsing context .

17. Return target browsing context 's WindowProxy object.

The open( url , target , features ) method on Window objects provides a mechanism for navigating an existing browsing context or opening and navigating an auxiliary browsing context .

When the method is invoked, the user agent must run the window open steps with url , target , and features .

To tokenize the features argument :

1. Let tokenizedFeatures be a new ordered map .

2. Let position point at the first code point of features .

3. While position is not past the end of features :

   1. Let name be the empty string.

   2. Let value be the empty string.

   3. Collect a sequence of code points that are feature separators from features given position . This skips past leading separators before the name.

   4. Collect a sequence of code points that are not feature separators from features given position . Set name to the collected characters, converted to ASCII lowercase .

   5. Set name to the result of normalizing the feature name name .

   6. While position is not past the end of features and the code point at position in features is not U+003D (=):

      1. If the code point at position in features is U+002C (,), or if it is not a feature separator , then break .

      2. Advance position by 1.

      This skips to the first U+003D (=) but does not skip past a U+002C (,) or a non-separator.

   7. If the code point at position in features is a feature separator :

      1. While position is not past the end of features and the code point at position in features is a feature separator :

         1. If the code point at position in features is U+002C (,), then break .

         2. Advance position by 1.

         This skips to the first non-separator but does not skip past a U+002C (,).

      2. Collect a sequence of code points that are not feature separators code points from features given position . Set value to the collected code points, converted to ASCII lowercase .

   8. If name is not the empty string, then set tokenizedFeatures [ name ] to value .

4. Return tokenizedFeatures .

A code point is a feature separator if it is ASCII whitespace , U+003D (=), or U+002C (,).

For legacy reasons, there are some aliases of some feature names. To normalize a feature name name , switch on name :

" screenx "

Return " left ".

" screeny "

Return " top ".

" innerwidth "

Return " width ".

" innerheight "

Return " height ".

Anything else

Return name .

To parse a boolean feature given a string value :

1. If value is the empty string, then return true.

2. If value is " yes ", then return true.

3. Let parsed be the result of parsing value as an integer .

4. If parsed is an error, then set it to 0.

5. Return false if parsed is 0, and true otherwise.

The name attribute's getter must run these steps:

1. If this Window object's browsing context is null, then return the empty string.

2. Return this Window object's browsing context 's name .

The name attribute's setter must run these steps:

1. If this Window object's browsing context is null, then return.

2. Set this Window object's browsing context 's name to the given value.

The name gets reset when the browsing context is navigated to another origin .

The close() method must run these steps:

1. Let current be this Window object's browsing context .

2. If current is null or its is closing is true, then return.

3. If all the following are true

   • current is script-closable
   • the incumbent global object 's browsing context is familiar with current
   • the incumbent global object 's browsing context is allowed to navigate current

   then:

   1. Set current 's is closing to true.

   2. Queue a task on the DOM manipulation task source to close current .

A browsing context is script-closable if it is an auxiliary browsing context that was created by a script (as opposed to by an action of the user), or if it is a top-level browsing context whose session history contains only one Document .

The closed attribute's getter must return true if this Window object's browsing context is null or its is closing is true, and false otherwise.

The stop() method must stop document loading given this Window object's associated Document .

7.3.2 Accessing other browsing contexts

window . length

Returns the number of document-tree child browsing contexts .

window [ index ]

Returns the indicated document-tree child browsing context .

The number of document-tree child browsing contexts of a Window object W is the result of running these steps:

1. If W 's browsing context is null, then return 0.

2. Return the number of document-tree child browsing contexts of W 's browsing context .

The length IDL attribute's getter must return the number of document-tree child browsing contexts of this Window object.

Indexed access to document-tree child browsing contexts is defined through the [[GetOwnProperty]] internal method of the WindowProxy object.

7.3.3 Named access on the Window object

window [ name ]

Returns the indicated element or collection of elements.

As a general rule, relying on this will lead to brittle code. Which IDs end up mapping to this API can vary over time, as new features are added to the web platform, for example. Instead of this, use document.getElementById() or document.querySelector() .

The document-tree child browsing context name property set of a Window object window is the return value of running these steps:

1. If window 's browsing context is null, then return the empty list.

2. Let childBrowsingContexts be all document-tree child browsing contexts of window 's browsing context whose browsing context name is not the empty string, in order, and including only the first document-tree child browsing context with a given name if multiple document-tree child browsing contexts have the same one.

3. Remove each browsing context from childBrowsingContexts whose active document 's origin is not same origin with window 's relevant settings object 's origin and whose browsing context name does not match the name of its container 's name content attribute value.

4. Return the browsing context names of childBrowsingContexts , in the same order.

<iframe src=https://elsewhere.example.com/></iframe>
<iframe
name=spices></iframe>

The Window object supports named properties . The supported property names of a Window object window at any moment consist of the following, in tree order according to the element that contributed them, ignoring later duplicates:

• window 's document-tree child browsing context name property set ;

• the value of the name content attribute for all embed , form , img , and object elements that have a non-empty name content attribute and are in a document tree with window 's associated Document as their root ; and

• the value of the id content attribute for all HTML elements that have a non-empty id content attribute and are in a document tree with window 's associated Document as their root .

To determine the value of a named property name in a Window object window , the user agent must return the value obtained using the following steps:

1. Let objects be the list of named objects of window with the name name .

   There will be at least one such object, by definition.

2. If objects contains a browsing context , then return the WindowProxy object of the nested browsing context of the first browsing context container in tree order whose nested browsing context is in objects .

3. Otherwise, if objects has only one element, return that element.

4. Otherwise return an HTMLCollection rooted at window 's associated Document , whose filter matches only named objects of window with the name name . (By definition, these will all be elements.)

Named objects of Window object window with the name name , for the purposes of the above algorithm, consist of the following:

• document-tree child browsing contexts of window 's associated Document whose name is name ;

• embed , form , img , or object elements that have a name content attribute whose value is name and are in a document tree with window 's associated Document as their root ; and

• HTML elements that have an id content attribute whose value is name and are in a document tree with window 's associated Document as their root .

7.3.4 Discarding browsing contexts

To discard a Document document :

1. Set document 's salvageable state to false.

2. Run any unloading document cleanup steps for document that are defined by this specification and other applicable specifications .

3. Abort document .

4. Remove any tasks associated with document in any task source , without running those tasks.

5. Discard all the child browsing contexts of document .

6. For each session history entry entry whose document is equal to document , set entry 's document to null.

7. Set document 's browsing context to null.

8. Remove document from the owner set of each WorkerGlobalScope object whose set contains document .

9. For each workletGlobalScope in document 's worklet global scopes , terminate workletGlobalScope .

To discard a browsing context browsingContext , run these steps:

1. Discard all Document objects for all the entries in browsingContext 's session history .

2. If browsingContext is a top-level browsing context , then remove browsingContext .

User agents may discard top-level browsing contexts at any time (typically, in response to user requests, e.g., when a user force-closes a window containing one or more top-level browsing contexts ). Other browsing contexts must be discarded once their WindowProxy object is eligible for garbage collection, in addition to the other places where this specification requires them to be discarded.

7.3.5 Closing browsing contexts

To close a browsing context browsingContext , run these steps:

1. Prompt to unload browsingContext 's active document . If the user refused to allow the document to be unloaded , then return.

2. Unload browsingContext 's active document .

3. Remove browsingContext from the user interface (e.g., close or hide its tab in a tabbed browser).

4. Discard browsingContext .

User agents should offer users the ability to arbitrarily close any top-level browsing context .

7.3.6 Browser interface elements

To allow web pages to integrate with web browsers, certain web browser interface elements are exposed in a limited way to scripts in web pages.

Each interface element is represented by a BarProp object:

[Exposed=Window]
interface BarProp {
  readonly attribute boolean visible;
};

window . locationbar . visible

Returns true if the location bar is visible; otherwise, returns false.

window . menubar . visible

Returns true if the menu bar is visible; otherwise, returns false.

window . personalbar . visible

Returns true if the personal bar is visible; otherwise, returns false.

window . scrollbars . visible

Returns true if the scrollbars are visible; otherwise, returns false.

window . statusbar . visible

Returns true if the status bar is visible; otherwise, returns false.

window . toolbar . visible

Returns true if the toolbar is visible; otherwise, returns false.

The visible attribute's getter must run these steps:

1. If this BarProp object's relevant global object 's browsing context is null, then return false.

2. If the user agent does not have a user interface element that the object represents, as described below, then return true.

3. Return true or a value determined by the user agent to most accurately represent the visibility state of the user interface element that the object represents, as described below.

The following BarProp objects must exist for each Window object:

The location bar BarProp object

Represents the user interface element that contains a control that displays the URL of the active document , or some similar interface concept.

The menu bar BarProp object

Represents the user interface element that contains a list of commands in menu form, or some similar interface concept.

The personal bar BarProp object

Represents the user interface element that contains links to the user's favorite pages, or some similar interface concept.

The scrollbar BarProp object

Represents the user interface element that contains a scrolling mechanism, or some similar interface concept.

The status bar BarProp object

Represents a user interface element found immediately below or after the document, as appropriate for the user's media, which typically provides information about ongoing network activity or information about elements that the user's pointing device is current indicating. If the user agent has no such user interface element, then the object may act as if the corresponding user interface element was absent (i.e. its visible attribute may return false).

The toolbar BarProp object

Represents the user interface element found immediately above or before the document, as appropriate for the user's media, which typically provides session history traversal controls (back and forward buttons, reload buttons, etc). If the user agent has no such user interface element, then the object may act as if the corresponding user interface element was absent (i.e. its visible attribute may return false).

The locationbar attribute must return the location bar BarProp object .

The menubar attribute must return the menu bar BarProp object .

The personalbar attribute must return the personal bar BarProp object .

The scrollbars attribute must return the scrollbar BarProp object .

The statusbar attribute must return the status bar BarProp object .

The toolbar attribute must return the toolbar BarProp object .

For historical reasons, the status attribute on the Window object must, on getting, return the last string it was set to, and on setting, must set itself to the new value. When the Window object is created, the attribute must be set to the empty string. It does not do anything else.

7.3.7 Script settings for Window objects

To set up a window environment settings object , given a JavaScript execution context execution context , null or an environment reservedEnvironment , a URL topLevelCreationURL , and an origin topLevelOrigin , run these steps:

1. Let realm be the value of execution context 's Realm component.

2. Let window be realm 's global object .

3. Let url be a copy of the URL of window 's associated Document .

4. Let settings object be a new environment settings object whose algorithms are defined as follows:

   The realm execution context

   Return execution context .

   The module map

   Return the module map of window 's associated Document .

   The responsible document

   Return window 's associated Document .

   The API URL character encoding

   Return the current character encoding of window 's associated Document .

   The API base URL

   Return the current base URL of window 's associated Document .

   The origin

   Return the origin of window 's associated Document .

   The referrer policy

   1. Let document be window 's associated Document .

   2. While document is an iframe srcdoc document and document 's referrer policy is the empty string, set document to document 's browsing context 's container document .

   3. Return document 's referrer policy .

   The embedder policy

   Return window 's associated Document 's embedder policy .

   The cross-origin isolated capability

   Return the logical conjunction of realm 's agent cluster 's cross-origin isolated and whether window 's associated Document is allowed to use the " cross-origin-isolated " feature.

5. If reservedEnvironment is non-null, then:

   1. Set settings object 's id to reservedEnvironment 's id , target browsing context to reservedEnvironment 's target browsing context , and active service worker to reservedEnvironment 's active service worker .

   2. Set reservedEnvironment 's id to the empty string.

      The identity of the reserved environment is considered to be fully transferred to the created environment settings object . The reserved environment is not searchable by the environment ’s id from this point on.

6. Otherwise, set settings object 's id to a new unique opaque string, settings object 's target browsing context to null, and settings object 's active service worker to null.

7. Set settings object 's creation URL to url , settings object 's top-level creation URL to topLevelCreationURL , and settings object 's top-level origin to topLevelOrigin .

8. Set realm 's [[HostDefined]] field to settings object .

7.4 The WindowProxy exotic object

A WindowProxy is an exotic object that wraps a Window ordinary object, indirecting most operations through to the wrapped object. Each browsing context has an associated WindowProxy object. When the browsing context is navigated , the Window object wrapped by the browsing context 's associated WindowProxy object is changed.

The WindowProxy exotic object must use the ordinary internal methods except where it is explicitly specified otherwise below.

There is no WindowProxy interface object .

Every WindowProxy object has a [[Window]] internal slot representing the wrapped Window object.

Although WindowProxy is named as a "proxy", it does not do polymorphic dispatch on its target's internal methods as a real proxy would, due to a desire to reuse machinery between WindowProxy and Location objects. As long as the Window object remains an ordinary object this is unobservable and can be implemented either way.

7.4.1 [[GetPrototypeOf]] ( )

1. Let W be the value of the [[Window]] internal slot of this .

2. If ! IsPlatformObjectSameOrigin ( W ) is true, then return ! OrdinaryGetPrototypeOf ( W ).

3. Return null.

7.4.2 [[SetPrototypeOf]] ( V )

1. Return ! SetImmutablePrototype ( this , V ).

7.4.3 [[IsExtensible]] ( )

1. Return true.

7.4.4 [[PreventExtensions]] ( )

1. Return false.

7.4.5 [[GetOwnProperty]] ( P )

1. Let W be the value of the [[Window]] internal slot of this .

2. If P is an array index property name , then:

   1. Let index be ! ToUint32 ( P ).

   2. Let maxProperties be the number of document-tree child browsing contexts of W .

   3. Let value be undefined.

   4. If maxProperties is greater than 0 and index is less than maxProperties , then set value to the WindowProxy object of the index th document-tree child browsing context of W 's browsing context , sorted in the order that their browsing context container elements were most recently inserted into W 's associated Document , the WindowProxy object of the most recently inserted browsing context container 's nested browsing context being last.

   5. If value is undefined, then:

      1. If ! IsPlatformObjectSameOrigin ( W ) is true, then return undefined.

      2. Throw a " SecurityError " DOMException .

   6. Return PropertyDescriptor { [[Value]]: value , [[Writable]]: false, [[Enumerable]]: true, [[Configurable]]: true }.

3. If ! IsPlatformObjectSameOrigin ( W ) is true, then return ! OrdinaryGetOwnProperty ( W , P ).

   This is a willful violation of the JavaScript specification's invariants of the essential internal methods to maintain compatibility with existing web content. See tc39/ecma262 issue #672 for more information. [JAVASCRIPT]

4. Let property be ! CrossOriginGetOwnPropertyHelper ( W , P ).

5. If property is not undefined, then return property .

6. If property is undefined and P is in W 's document-tree child browsing context name property set , then:

   1. Let value be the WindowProxy object of the named object of W with the name P .

   2. Return PropertyDescriptor { [[Value]]: value , [[Enumerable]]: false, [[Writable]]: false, [[Configurable]]: true }.

      The reason the property descriptors are non-enumerable, despite this mismatching the same-origin behavior, is for compatibility with existing web content. See issue #3183 for details.

7. Return ? CrossOriginPropertyFallback ( P ).

7.4.6 [[DefineOwnProperty]] ( P , Desc )

1. Let W be the value of the [[Window]] internal slot of this .

2. If ! IsPlatformObjectSameOrigin ( W ) is true, then:

   1. If P is an array index property name , return false.

   2. Return ? OrdinaryDefineOwnProperty ( W , P , Desc ).

      This is a willful violation of the JavaScript specification's invariants of the essential internal methods to maintain compatibility with existing web content. See tc39/ecma262 issue #672 for more information. [JAVASCRIPT]

3. Throw a " SecurityError " DOMException .

7.4.7 [[Get]] ( P , Receiver )

1. Let W be the value of the [[Window]] internal slot of this .

2. Check if an access between two browsing contexts should be reported , given the current global object 's browsing context , W 's browsing context , P , and the current settings object .

3. If ! IsPlatformObjectSameOrigin ( W ) is true, then return ? OrdinaryGet ( this , P , Receiver ).

4. Return ? CrossOriginGet ( this , P , Receiver ).

this is passed rather than W as OrdinaryGet and CrossOriginGet will invoke the [[GetOwnProperty]] internal method.

7.4.8 [[Set]] ( P , V , Receiver )

1. Let W be the value of the [[Window]] internal slot of this .

2. Check if an access between two browsing contexts should be reported , given the current global object 's browsing context , W 's browsing context , P , and the current settings object .

3. If ! IsPlatformObjectSameOrigin ( W ) is true, then return ? OrdinarySet ( this , P , V , Receiver ).

4. Return ? CrossOriginSet ( this , P , V , Receiver ).

this is passed rather than W as OrdinarySet and CrossOriginSet will invoke the [[GetOwnProperty]] internal method. OrdinarySet will also invoke the [[DefineOwnProperty]] internal method.

7.4.9 [[Delete]] ( P )

1. Let W be the value of the [[Window]] internal slot of this .

2. If ! IsPlatformObjectSameOrigin ( W ) is true, then:

   1. If P is an array index property name , then:

      1. Let desc be ! this .[[GetOwnProperty]]( P ).

      2. If desc is undefined, then return true.

      3. Return false.

   2. Return ? OrdinaryDelete ( W , P ).

3. Throw a " SecurityError " DOMException .

7.4.10 [[OwnPropertyKeys]] ( )

1. Let W be the value of the [[Window]] internal slot of this .

2. Let keys be a new empty List .

3. Let maxProperties be the number of document-tree child browsing contexts of W .

4. Let index be 0.

5. Repeat while index < maxProperties ,

   1. Add ! ToString ( index ) as the last element of keys .

   2. Increment index by 1.

6. If ! IsPlatformObjectSameOrigin ( W ) is true, then return the concatenation of keys and ! OrdinaryOwnPropertyKeys ( W ).

7. Return the concatenation of keys and ! CrossOriginOwnPropertyKeys ( W ).