method TracingChannel.prototype.traceCallback
Unstable
Usage in Deno
```typescript import { TracingChannel } from "node:node__diagnostics_channel.d.ts"; ```
TracingChannel.prototype.traceCallback<Fn extends (this: any,...args: any[],) => any>(fn: Fn,position?: number,context?: ContextType,thisArg?: any,...args: Parameters<Fn>,): 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;
});
```
void
The return value of the given function