EventSource extension type
The EventSource interface is web content's interface to
server-sent events.
An EventSource instance opens a persistent connection to an
HTTP server, which
sends
events
in text/event-stream format. The connection remains open until closed by
calling EventSource.close.
Once the connection is opened, incoming messages from the server are
delivered to your code in the form of events. If there is an event field in
the incoming message, the triggered event is the same as the event field
value. If no event field is present, then a generic
EventSource/message_event event is fired.
Unlike
WebSockets,
server-sent events are unidirectional; that is, data messages are delivered
in one direction, from the server to the client (such as a user's web
browser). That makes them an excellent choice when there's no need to send
data from the client to the server in message form. For example,
EventSource is a useful approach for handling things like social media
status updates, news feeds, or delivering data into a
client-side storage
mechanism like
IndexedDB
or
web storage.
Warning: When not used over HTTP/2, SSE suffers from a limitation to the maximum number of open connections, which can be specially painful when opening various tabs as the limit is per browser and set to a very low number (6). The issue has been marked as "Won't fix" in Chrome and Firefox. This limit is per browser + domain, so that means that you can open 6 SSE connections across all of the tabs to
www.example1.comand another 6 SSE connections towww.example2.com. (from Stackoverflow). When using HTTP/2, the maximum number of simultaneous HTTP streams is negotiated between the server and the client (defaults to 100).
- on
- Implemented types
Constructors
- EventSource(String url, [EventSourceInit eventSourceInitDict])
-
factory
Properties
- hashCode → int
-
The hash code for this object.
no setterinherited
- onerror ↔ EventHandler?
-
getter/setter pair
- onmessage ↔ EventHandler?
-
getter/setter pair
- onopen ↔ EventHandler?
-
getter/setter pair
- readyState → int
-
no setter
- runtimeType → Type
-
A representation of the runtime type of the object.
no setterinherited
- url → String
-
no setter
- withCredentials → bool
-
no setter
Methods
-
addEventListener(
String type, EventListener? callback, [JSAny options]) → void -
The
addEventListener()method of the EventTarget interface sets up a function that will be called whenever the specified event is delivered to the target.inherited -
close(
) → void -
The
close()method of the EventSource interface closes the connection, if one is made, and sets the EventSource.readyState attribute to2(closed). -
dispatchEvent(
Event event) → bool -
The
dispatchEvent()method of the EventTarget sends an Event to the object, (synchronously) invoking the affected event listeners in the appropriate order. The normal event processing rules (including the capturing and optional bubbling phase) also apply to events dispatched manually withdispatchEvent().inherited -
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a nonexistent method or property is accessed.
inherited
-
removeEventListener(
String type, EventListener? callback, [JSAny options]) → void -
The
removeEventListener()method of the EventTarget interface removes an event listener previously registered with EventTarget.addEventListener from the target. The event listener to be removed is identified using a combination of the event type, the event listener function itself, and various optional options that may affect the matching process; see Matching event listeners for removal.inherited -
toString(
) → String -
A string representation of this object.
inherited
Operators
-
operator ==(
Object other) → bool -
The equality operator.
inherited