Usage in Deno
```typescript import { TracingChannel } from "node:node__diagnostics_channel.d.ts"; ```The class `TracingChannel` is a collection of `TracingChannel Channels` which
together express a single traceable action. It is used to formalize and
simplify the process of producing events for tracing application flow. [tracingChannel](../.././node__diagnostics_channel.d.ts/~/tracingChannel) is used to construct a `TracingChannel`. As with `Channel` it is recommended to create and reuse a
single `TracingChannel` at the top-level of the file rather than creating them
dynamically.
subscribe(subscribers: TracingChannelSubscribers<ContextType>): void
Helper to subscribe a collection of functions to the corresponding channels.
This is the same as calling `channel.subscribe(onMessage)` on each channel
individually.
```js
import diagnostics_channel from 'node:diagnostics_channel';
const channels = diagnostics_channel.tracingChannel('my-channel');
channels.subscribe({
start(message) {
// Handle start message
},
end(message) {
// Handle end message
},
asyncStart(message) {
// Handle asyncStart message
},
asyncEnd(message) {
// Handle asyncEnd message
},
error(message) {
// Handle error message
},
});
```
traceCallback<Fn extends (this: any,...args: any[],) => any>(): void
Trace a callback-receiving function call. This will always produce a `start event` and `end event` around the synchronous portion of the
function execution, and will produce a `asyncStart event` and `asyncEnd event` around the callback execution. It may also produce an `error event` if the given function throws an error or
the returned
promise rejects. This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all
events should have any bound stores set to match this trace context.
The `position` will be -1 by default to indicate the final argument should
be used as the callback.
```js
import diagnostics_channel from 'node:diagnostics_channel';
const channels = diagnostics_channel.tracingChannel('my-channel');
channels.traceCallback((arg1, callback) => {
// Do something
callback(null, 'result');
}, 1, {
some: 'thing',
}, thisArg, arg1, callback);
```
The callback will also be run with `channel.runStores(context, ...)` which
enables context loss recovery in some cases.
To ensure only correct trace graphs are formed, events will only be published if subscribers are present prior to starting the trace. Subscriptions
which are added after the trace begins will not receive future events from that trace, only future traces will be seen.
```js
import diagnostics_channel from 'node:diagnostics_channel';
import { AsyncLocalStorage } from 'node:async_hooks';
const channels = diagnostics_channel.tracingChannel('my-channel');
const myStore = new AsyncLocalStorage();
// The start channel sets the initial store data to something
// and stores that store data value on the trace context object
channels.start.bindStore(myStore, (data) => {
const span = new Span(data);
data.span = span;
return span;
});
// Then asyncStart can restore from that data it stored previously
channels.asyncStart.bindStore(myStore, (data) => {
return data.span;
});
```
tracePromise<ThisArg = any,Args extends any[] = any[],>(fn: (this: ThisArg,...args: Args,) => Promise<any>,context?: ContextType,thisArg?: ThisArg,...args: Args,): void
Trace a promise-returning function call. This will always produce a `start event` and `end event` around the synchronous portion of the
function execution, and will produce an `asyncStart event` and `asyncEnd event` when a promise continuation is reached. It may also
produce an `error event` if the given function throws an error or the
returned promise rejects. This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all
events should have any bound stores set to match this trace context.
To ensure only correct trace graphs are formed, events will only be published if subscribers are present prior to starting the trace. Subscriptions
which are added after the trace begins will not receive future events from that trace, only future traces will be seen.
```js
import diagnostics_channel from 'node:diagnostics_channel';
const channels = diagnostics_channel.tracingChannel('my-channel');
channels.tracePromise(async () => {
// Do something
}, {
some: 'thing',
});
```
traceSync<ThisArg = any,Args extends any[] = any[],>(): void
Trace a synchronous function call. This will always produce a `start event` and `end event` around the execution and may produce an `error event` if the given function throws an error.
This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all
events should have any bound stores set to match this trace context.
To ensure only correct trace graphs are formed, events will only be published if subscribers are present prior to starting the trace. Subscriptions
which are added after the trace begins will not receive future events from that trace, only future traces will be seen.
```js
import diagnostics_channel from 'node:diagnostics_channel';
const channels = diagnostics_channel.tracingChannel('my-channel');
channels.traceSync(() => {
// Do something
}, {
some: 'thing',
});
```
unsubscribe(subscribers: TracingChannelSubscribers<ContextType>): void
Helper to unsubscribe a collection of functions from the corresponding channels.
This is the same as calling `channel.unsubscribe(onMessage)` on each channel
individually.
```js
import diagnostics_channel from 'node:diagnostics_channel';
const channels = diagnostics_channel.tracingChannel('my-channel');
channels.unsubscribe({
start(message) {
// Handle start message
},
end(message) {
// Handle end message
},
asyncStart(message) {
// Handle asyncStart message
},
asyncEnd(message) {
// Handle asyncEnd message
},
error(message) {
// Handle error message
},
});
```