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Add a timezonechange event to Window/WorkerGlobalScope
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The current timezone is visible to JavaScript and changes over time.
Changes may be useful to note, e.g., in a long-running calendar or mail
application that may want to update dates and times without refreshing
when the user resumes using the application after travel.
Currently, to accomplish that, a webapp would have to poll, e.g.,
by repeatedly calling `Intl.DateTimeFormat().resolvedOptions().timeZone`.
With this patch, an event would instead notify the application.

In this patch, the time zone may change before the task is run, but
must be changed at the point the task is run. A previous version included
additional guarantees, that the time zone would not be changed until the
start of the task, but these semantics add implementation complexity and
no concrete use case was found for the greater guarantees.
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@littledan
littledan committed Oct 23, 2018
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Expand Up @@ -3072,6 +3072,8 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-copydatablockbytes">CopyDataBlockBytes</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-createbytedatablock">CreateByteDataBlock</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-createdataproperty">CreateDataProperty</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-daylight-saving-time-adjustment">DaylightSavingsTA</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma402/#sec-defaulttimezone">DefaultTimeZone</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-detacharraybuffer">DetachArrayBuffer</dfn> abstract operation</li>
<li>The <dfn data-x="js-EnqueueJob" data-x-href="https://tc39.github.io/ecma262/#sec-enqueuejob">EnqueueJob</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-enumerableownproperties">EnumerableOwnProperties</dfn> abstract operation</li>
Expand All @@ -3084,12 +3086,14 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
<li>The <dfn data-x="js-HostPromiseRejectionTracker" data-x-href="https://tc39.github.io/ecma262/#sec-host-promise-rejection-tracker">HostPromiseRejectionTracker</dfn> abstract operation</li>
<li>The <dfn data-x="js-HostResolveImportedModule" data-x-href="https://tc39.github.io/ecma262/#sec-hostresolveimportedmodule">HostResolveImportedModule</dfn> abstract operation</li>
<li>The <dfn data-x="js-InitializeHostDefinedRealm" data-x-href="https://tc39.github.io/ecma262/#sec-initializehostdefinedrealm">InitializeHostDefinedRealm</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma402/#datetimeformat-objects">Intl.DateTimeFormat</dfn> constructor</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-isaccessordescriptor">IsAccessorDescriptor</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-iscallable">IsCallable</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-isconstructor">IsConstructor</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-isdatadescriptor">IsDataDescriptor</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-isdetachedbuffer">IsDetachedBuffer</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-issharedarraybuffer">IsSharedArrayBuffer</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-local-time-zone-adjustment">LocalTZA</dfn> abstract operation</li>
<li>The <dfn data-x="js-NewObjectEnvironment" data-x-href="https://tc39.github.io/ecma262/#sec-newobjectenvironment">NewObjectEnvironment</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-normalcompletion">NormalCompletion</dfn> abstract operation</li>
<!-- the next set of Ordinary* abstract operations are in order of appearance -->
Expand Down Expand Up @@ -15261,6 +15265,7 @@ interface <dfn>HTMLStyleElement</dfn> : <span>HTMLElement</span> {
<dd><code data-x="handler-window-onbeforeunload">onbeforeunload</code></dd>
<dd><code data-x="handler-window-onhashchange">onhashchange</code></dd>
<dd><code data-x="handler-window-onlanguagechange">onlanguagechange</code></dd>
<dd><code data-x="handler-window-ontimezonechange">ontimezonechange</code></dd>
<dd><code data-x="handler-window-onmessage">onmessage</code></dd>
<dd><code data-x="handler-window-onmessageerror">onmessageerror</code></dd>
<dd><code data-x="handler-window-onoffline">onoffline</code></dd>
Expand Down Expand Up @@ -89024,6 +89029,25 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {

</ol>

<h5>Time zone changes</h5>

<p>JavaScript programs can observe the current time zone. <code>Date</code> uses the time zone
through the <code>LocalTZA</code> and <code>DaylightSavingsTA</code> algorithms.
<code>Intl.DateTimeFormat</code> uses the time zone in its <code>DefaultTimeZone</code> algorithm.
Although it is not explicitly stated in the JavaScript specification, user agents may update the
current time zone over the execution of a page as the user's time zone changes, providing
different results for these algorithms over time.</p>

<p>When a UA has a new time zone to present to JavaScript, as would be observable by any of
those algorithms, the user agent must
<span>queue a task</span> to <span data-x="concept-event-fire">fire an event</span> named <code
data-x="event-timezonechange">timezonechange</code> at the <code>Window</code> or
<code>WorkerGlobalScope</code> object. The new time zone must be observable by JavaScript at the
point the task begins, and it may be observable earlier.</p>

<p>The <span>task source</span> for this <span data-x="concept-task">task</span> is the
<span>DOM manipulation task source</span>.</p>

<div w-nodev>

<h4>Event loops</h4> <!-- <dfn>event loop</dfn> -->
Expand Down Expand Up @@ -90725,6 +90749,7 @@ typedef <span>OnBeforeUnloadEventHandlerNonNull</span>? <dfn>OnBeforeUnloadEvent
<tr><td><dfn><code data-x="handler-window-onbeforeunload">onbeforeunload</code></dfn> <td> <code data-x="event-beforeunload">beforeunload</code>
<tr><td><dfn><code data-x="handler-window-onhashchange">onhashchange</code></dfn> <td> <code data-x="event-hashchange">hashchange</code> <!-- new -->
<tr><td><dfn><code data-x="handler-window-onlanguagechange">onlanguagechange</code></dfn> <td> <code data-x="event-languagechange">languagechange</code> <!-- new -->
<tr><td><dfn><code data-x="handler-window-ontimezonechange">ontimezonechange</code></dfn> <td> <code data-x="event-timezonechange">timezonechange</code> <!-- new -->
<tr><td><dfn><code data-x="handler-window-onmessage">onmessage</code></dfn> <td> <code data-x="event-message">message</code> <!-- new for postMessage -->
<tr><td><dfn><code data-x="handler-window-onmessageerror">onmessageerror</code></dfn> <td> <code data-x="event-messageerror">messageerror</code> <!-- new for SAB -->
<tr><td><dfn><code data-x="handler-window-onoffline">onoffline</code></dfn> <td> <code data-x="event-offline">offline</code> <!-- new -->
Expand Down Expand Up @@ -90858,6 +90883,7 @@ interface mixin <dfn>WindowEventHandlers</dfn> {
attribute <span>OnBeforeUnloadEventHandler</span> <span data-x="handler-window-onbeforeunload">onbeforeunload</span>;
attribute <span>EventHandler</span> <span data-x="handler-window-onhashchange">onhashchange</span>;
attribute <span>EventHandler</span> <span data-x="handler-window-onlanguagechange">onlanguagechange</span>;
attribute <span>EventHandler</span> <span data-x="handler-window-ontimezonechange">ontimezonechange</span>;
attribute <span>EventHandler</span> <span data-x="handler-window-onmessage">onmessage</span>;
attribute <span>EventHandler</span> <span data-x="handler-window-onmessageerror">onmessageerror</span>;
attribute <span>EventHandler</span> <span data-x="handler-window-onoffline">onoffline</span>;
Expand Down Expand Up @@ -97434,6 +97460,7 @@ interface <dfn>WorkerGlobalScope</dfn> : <span>EventTarget</span> {

attribute <span>OnErrorEventHandler</span> <span data-x="handler-WorkerGlobalScope-onerror">onerror</span>;
attribute <span>EventHandler</span> <span data-x="handler-WorkerGlobalScope-onlanguagechange">onlanguagechange</span>;
attribute <span>EventHandler</span> <span data-x="handler-WorkerGlobalScope-ontimezonechange">ontimezonechange</span>;
attribute <span>EventHandler</span> <span data-x="handler-WorkerGlobalScope-onoffline">onoffline</span>;
attribute <span>EventHandler</span> <span data-x="handler-WorkerGlobalScope-ononline">ononline</span>;
attribute <span>EventHandler</span> <span data-x="handler-WorkerGlobalScope-onrejectionhandled">onrejectionhandled</span>;
Expand Down Expand Up @@ -97543,6 +97570,7 @@ interface <dfn>WorkerGlobalScope</dfn> : <span>EventTarget</span> {
<tbody>
<tr><td><dfn><code data-x="handler-WorkerGlobalScope-onerror">onerror</code></dfn> <td> <code data-x="event-error">error</code>
<tr><td><dfn><code data-x="handler-WorkerGlobalScope-onlanguagechange">onlanguagechange</code></dfn> <td> <code data-x="event-languagechange">languagechange</code> <!-- new -->
<tr><td><dfn><code data-x="handler-WorkerGlobalScope-ontimezonechange">ontimezonechange</code></dfn> <td> <code data-x="event-timezonechange">timezonechange</code>
<tr><td><dfn><code data-x="handler-WorkerGlobalScope-onoffline">onoffline</code></dfn> <td> <code data-x="event-offline">offline</code> <!-- new -->
<tr><td><dfn><code data-x="handler-WorkerGlobalScope-ononline">ononline</code></dfn> <td> <code data-x="event-online">online</code> <!-- new -->
<tr><td><dfn><code data-x="handler-WorkerGlobalScope-onrejectionhandled">onrejectionhandled</code></dfn> <td> <code data-x="event-rejectionhandled">rejectionhandled</code>
Expand Down Expand Up @@ -116653,6 +116681,7 @@ interface <dfn>External</dfn> {
<code data-x="handler-window-onbeforeunload">onbeforeunload</code>;
<code data-x="handler-window-onhashchange">onhashchange</code>;
<code data-x="handler-window-onlanguagechange">onlanguagechange</code>;
<code data-x="handler-window-ontimezonechange">ontimezonechange</code>;
<code data-x="handler-window-onmessage">onmessage</code>;
<code data-x="handler-window-onmessageerror">onmessageerror</code>;
<code data-x="handler-window-onoffline">onoffline</code>;
Expand Down Expand Up @@ -119724,6 +119753,12 @@ interface <dfn>External</dfn> {
<td> <code data-x="event-languagechange">languagechange</code> event handler for <code>Window</code> object
<td> <span data-x="event handler content attributes">Event handler content attribute</span>

<tr>
<th id="ix-handler-window-ontimezonechange"> <code data-x="">ontimezonechange</code>
<td> <code data-x="handler-window-ontimezonechange">body</code>
<td> <code data-x="event-timezonechange">timezonechange</code> event handler for <code>Window</code> object
<td> <span data-x="event handler content attributes">Event handler content attribute</span>

<tr>
<th id="ix-handler-onload"> <code data-x="">onload</code>
<td> <span data-x="handler-onload">HTML elements</span>
Expand Down Expand Up @@ -120599,6 +120634,12 @@ INSERT INTERFACES HERE
<td> Global scope objects
<td> Fired at the global scope object when the user's preferred languages change

<tr> <!-- timezonechange -->
<td> <dfn data-dfn-type="event" data-dfn-for="Window,WorkerGlobalScope" data-export=""><code data-x="event-timezonechange">timezonechange</code></dfn>
<td> <code>Event</code>
<td> Global scope objects
<td> Fired at the global scope object when the user's current timezone changes

<tr> <!-- load -->
<td> <dfn data-dfn-type="event" data-dfn-for="Window,HTMLElement" data-export=""><code data-x="event-load">load</code></dfn>
<td> <code>Event</code>
Expand Down

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