ReadonlyhasCheck if there are active subscribers to this channel. This is helpful if the message you want to send might be expensive to prepare.
This API is optional but helpful when trying to publish messages from very performance-sensitive code.
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
if (channel.hasSubscribers) {
// There are subscribers, prepare and publish message
}
ReadonlynameExperimentalWhen channel.runStores(context, ...) is called, the given context data
will be applied to any store bound to the channel. If the store has already been
bound the previous transform function will be replaced with the new one.
The transform function may be omitted to set the given context data as the
context directly.
import diagnostics_channel from 'node:diagnostics_channel';
import { AsyncLocalStorage } from 'node:async_hooks';
const store = new AsyncLocalStorage();
const channel = diagnostics_channel.channel('my-channel');
channel.bindStore(store, (data) => {
return { data };
});
The store to which to bind the context data
Optionaltransform: (context: ContextType) => StoreTypeTransform context data before setting the store context
Publish a message to any subscribers to the channel. This will trigger message handlers synchronously so they will execute within the same context.
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
channel.publish({
some: 'message',
});
The message to send to the channel subscribers
ExperimentalApplies the given data to any AsyncLocalStorage instances bound to the channel for the duration of the given function, then publishes to the channel within the scope of that data is applied to the stores.
If a transform function was given to channel.bindStore(store) it will be
applied to transform the message data before it becomes the context value for
the store. The prior storage context is accessible from within the transform
function in cases where context linking is required.
The context applied to the store should be accessible in any async code which
continues from execution which began during the given function, however
there are some situations in which context loss may occur.
import diagnostics_channel from 'node:diagnostics_channel';
import { AsyncLocalStorage } from 'node:async_hooks';
const store = new AsyncLocalStorage();
const channel = diagnostics_channel.channel('my-channel');
channel.bindStore(store, (message) => {
const parent = store.getStore();
return new Span(message, parent);
});
channel.runStores({ some: 'message' }, () => {
store.getStore(); // Span({ some: 'message' })
});
Register a message handler to subscribe to this channel. This message handler
will be run synchronously whenever a message is published to the channel. Any
errors thrown in the message handler will trigger an 'uncaughtException'.
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
channel.subscribe((message, name) => {
// Received data
});
The handler to receive channel messages
ExperimentalRemove a message handler previously registered to this channel with channel.bindStore(store).
import diagnostics_channel from 'node:diagnostics_channel';
import { AsyncLocalStorage } from 'node:async_hooks';
const store = new AsyncLocalStorage();
const channel = diagnostics_channel.channel('my-channel');
channel.bindStore(store);
channel.unbindStore(store);
The store to unbind from the channel.
true if the store was found, false otherwise.
Remove a message handler previously registered to this channel with channel.subscribe(onMessage).
import diagnostics_channel from 'node:diagnostics_channel';
const channel = diagnostics_channel.channel('my-channel');
function onMessage(message, name) {
// Received data
}
channel.subscribe(onMessage);
channel.unsubscribe(onMessage);
The previous subscribed handler to remove
true if the handler was found, false otherwise.
The class
Channelrepresents an individual named channel within the data pipeline. It is used to track subscribers and to publish messages when there are subscribers present. It exists as a separate object to avoid channel lookups at publish time, enabling very fast publish speeds and allowing for heavy use while incurring very minimal cost. Channels are created with channel, constructing a channel directly withnew Channel(name)is not supported.Since
v15.1.0, v14.17.0