Jint

Events and messaging ​

Events ​

WebApiFeatures.Events installs Event, CustomEvent, EventTarget, AbortController, and AbortSignal. Jint has no DOM tree, so an EventTarget dispatches to itself without capture or bubble ancestors while retaining listener ordering, once, removal, and propagation rules.

An event listener that throws erupts unless a DiagnosticsSink is configured; with a sink, Jint reports it and continues to later listeners. WebApiFeatures.GlobalEvents adds global error, unhandledrejection, and rejectionhandled handling. Script may observe those reports but cannot suppress the host diagnostics sink or turn a constraint failure into an event.

Bridge a host token without running script on the cancelling thread:

csharp
JsValue signal = engine.WebApi.CreateAbortSignal(cancellationToken);
engine.SetValue("signal", signal);

Cancellation enqueues the abort for the next pump. An already-cancelled token creates an already-aborted signal.

Message channels ​

MessageChannel, MessagePort, and BroadcastChannel use structured clone. Messages are copied when posted; ArrayBuffer, MessagePort, and streams can be transferred. Transferred values become unusable on the sender.

A port queue does not deliver until start() or an onmessage assignment; addEventListener alone does not start it. Delivery is an event-loop task and requires the receiving engine to be pumped.

Connect two engines without sharing any JsValue:

csharp
var pair = first.WebApi.CreateMessagePortPair(second);
first.SetValue("port", pair.Local);
second.SetValue("port", pair.Remote);

first.Execute("port.postMessage({ value: 21 })");
second.Tasks.ProcessTasks();

Each side serializes and deserializes on its own engine thread. A global snapshot restore ends ports created in the previous cycle, so pooled engines need fresh channels.

BroadcastChannel is private to an engine by default. Assign the same thread-safe BroadcastChannelBroker to options.WebApi.Messaging.Broker for explicitly shared channels. Close short-lived channels; a shared broker retains its subscribers until close, engine restore, or disposal.

See Workers for worker messaging and Encoding, files, and streams for transferable streams.