Zone.js's support for standard apis

Zone.js patches most standard APIs, such as DOM event listeners and XMLHttpRequest in the browser, as well as EventEmitter and the fs API in Node.js, so they can operate within a zone.

In this document, all patched API are listed.

For non-standard APIs, please see NON-STANDARD-APIS.md

Patch Mechanisms

There are several patch mechanisms:

Wrap: Makes callbacks run in zones, allowing applications to receive onInvoke and onIntercept callbacks.
Task: Similar to the JavaScript VM, applications can receive onScheduleTask, onInvokeTask, onCancelTask, and onHasTask callbacks:
1. MacroTask
2. MicroTask
3. EventTask

Some APIs which should be treated as Tasks, but are currently still patched in the wrap way.

Browser

Web APIs

API	Patch Mechanism	Others
setTimeout/clearTimeout	MacroTask	app can get handlerId, interval, args, isPeriodic(false) through task.data
setImmediate/clearImmediate	MacroTask	same with setTimeout
setInterval/clearInterval	MacroTask	isPeriodic is true, so setInterval will not trigger onHasTask callback
requestAnimationFrame/cancelAnimationFrame	MacroTask
mozRequestAnimationFrame/mozCancelAnimationFrame	MacroTask
webkitRequestAnimationFrame/webkitCancelAnimationFrame	MacroTask
alert	wrap
prompt	wrap
confirm	wrap
Promise	MicroTask
EventTarget	EventTask	see below Event Target for more details
HTMLElement on properties	EventTask	see below on properties for more details
XMLHttpRequest.send/abort	MacroTask
XMLHttpRequest on properties	EventTask
IDBIndex on properties	EventTask
IDBRequest on properties	EventTask
IDBOpenDBRequest on properties	EventTask
IDBDatabaseRequest on properties	EventTask
IDBTransaction on properties	EventTask
IDBCursor on properties	EventTask
WebSocket on properties	EventTask
MutationObserver	wrap
WebkitMutationObserver	wrap
FileReader	wrap
registerElement	wrap

`EventTarget`

For browsers supporting EventTarget, Zone.js just patches EventTarget, so everything that inherits from EventTarget will also be patched.
For browsers that do not support EventTarget, Zone.js will patch the following APIs in the IDL that inherit from EventTarget


ApplicationCache	EventSource	FileReader	InputMethodContext
MediaController	MessagePort	Node	Performance
SVGElementInstance	SharedWorker	TextTrack	TextTrackCue
TextTrackList	WebKitNamedFlow	Window	Worker
WorkerGlobalScope	XMLHttpRequest	XMLHttpRequestEventTarget	XMLHttpRequestUpload
IDBRequest	IDBOpenDBRequest	IDBDatabase	IDBTransaction
IDBCursor	DBIndex	WebSocket

The following on properties, such as onclick, onreadystatechange, are patched in zone.js as EventTasks:


copy	cut	paste	abort
blur	focus	canplay	canplaythrough
change	click	contextmenu	dblclick
drag	dragend	dragenter	dragleave
dragover	dragstart	drop	durationchange
emptied	ended	input	invalid
keydown	keypress	keyup	load
loadeddata	loadedmetadata	loadstart	message
mousedown	mouseenter	mouseleave	mousemove
mouseout	mouseover	mouseup	pause
play	playing	progress	ratechange
reset	scroll	seeked	seeking
select	show	stalled	submit
suspend	timeupdate	volumechange	waiting
mozfullscreenchange	mozfullscreenerror	mozpointerlockchange	mozpointerlockerror
error	webglcontextrestored	webglcontextlost	webglcontextcreationerror

NodeJS

API	Patch Mechanism	Others
setTimeout/clearTimeout	MacroTask	app can get handlerId, interval, args, isPeriodic(false) through task.data
setImmediate/clearImmediate	MacroTask	same with setTimeout
setInterval/clearInterval	MacroTask	isPeriodic is true, so setInterval will not trigger onHasTask callback
process.nextTick	Microtask	isPeriodic is true, so setInterval will not trigger onHasTask callback
Promise	MicroTask
EventEmitter	EventTask	All APIs inherit EventEmitter are patched as EventTask
crypto	MacroTask
fs	MacroTask	all async methods are patched

EventEmitter, addEventListener, prependEventListener, and on will be patched once as EventTasks, while removeEventListener and removeAllListeners will remove those EventTasks.

Electron

Zone.js does not patch the Electron API. However, in Electron, both browser APIs and Node APIs are patched. Therefore, if you want to include Zone.js in an Electron application, please use dist/zone-mix.js.

ZoneAwareError

ZoneAwareError replaces the global Error and adds zone information to the stack trace. It also addresses the 'this' issue. This problem can occur when creating an error without new: this will be undefined in strict mode and global in non-strict mode, potentially leading to difficult-to-detect issues.

const error = Error();

ZoneAwareError makes sure that this is ZoneAwareError even without new.

ZoneAwarePromise

ZoneAwarePromise wraps the global Promise and allows it to run in zones as a MicroTask. It also passes mostly all Promise A+ tests.

UnpatchedEvents

Event unpatching means calling the native implementation immediately, without any additional functionality such as task tracking, zone capturing, etc.

Sometimes we don't want certain events to be patched by zone.js. We can instruct zone.js to leave these events.

This can be done through __Zone_ignore_on_properties and __zone_symbol__UNPATCHED_EVENTS, which should be available on the window object. It is usually recommended to declare these lists in the <head> element before your code is loaded. Once the zone.js code is executed and all the patches are initialized, the __Zone_ignore_on_properties and __zone_symbol__UNPATCHED_EVENTS lists will no longer be read:

<head>
  <script>
    // Disable patching `on` properties for the following targets:
    const targets = [
      window,
      Document.prototype,
      HTMLBodyElement.prototype,
      HTMLElement.prototype,
    ];

    // This is declared without `let` or `const`, so it will become a property
    // of the global `window` object:
    __Zone_ignore_on_properties = [];

    // For the following targets, the `onscroll` property will not be patched.
    // Therefore, when using `window.onscroll = () => {}`, the callback will
    // always be invoked inside the root zone, because the implementation is not
    // patched and the task is not tracked for the current target:
    targets.forEach((target) => {
      __Zone_ignore_on_properties.push({
        target: target,
        ignoreProperties: ['scroll'],
      });
    });

    // When calling `addEventListener` with the `scroll` event, `zone.js` will
    // invoke the native browser `addEventListener` implementation immediately:
    __zone_symbol__UNPATCHED_EVENTS = ['scroll'];
  </script>
</head>

When we declare events in __zone_symbol__UNPATCHED_EVENTS, their callbacks will not be intercepted by zone.js, since zone.js calls the native addEventListener of the EventTarget (not the patched function):

__zone_symbol__UNPATCHED_EVENTS = ['scroll'];

Zone.current.fork({ name: 'child' }).run(() => {
  window.addEventListener('scroll', () => {
    console.log(Zone.current); // <root>
  });
});

Note that for __Zone_ignore_on_properties, we need to specify object prototypes (like Document.prototype), with window being the exception. This is because on properties are part of the prototypes.

When the target is Document.prototype and ignoreProperties is a list containing ['scroll'], then document.onscroll will not be patched.

Note that __Zone_ignore_on_properties allows for individually unpatching events, but this only applies to on properties. In contrast, __zone_symbol__UNPATCHED_EVENTS affects all events with the specified name. For example, if you're dealing with a library that uses FileReader and sets the load event using reader.onload = () => { ... }, you can simply use __Zone_ignore_on_properties = [{ target: FileReader.prototype, ignoreProperties: ['load'] }]. However, if the library adds a load event listener using addEventListener, you would need to use __zone_symbol__UNPATCHED_EVENTS = ['load'], which would affect other targets as well. For instance, the load event of XMLHttpRequest would also be unpatched.

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