Usage in Deno
```typescript import * as mod from "node:node__trace_events.d.ts"; ```> [!WARNING] Deno compatibility
> All exports are non-functional stubs.
The `node:trace_events` module provides a mechanism to centralize tracing information
generated by V8, Node.js core, and userspace code.
Tracing can be enabled with the `--trace-event-categories` command-line flag
or by using the `trace_events` module. The `--trace-event-categories` flag
accepts a list of comma-separated category names.
The available categories are:
* `node`: An empty placeholder.
* `node.async_hooks`: Enables capture of detailed [`async_hooks`](https://nodejs.org/docs/latest-v22.x/api/async_hooks.html) trace data.
The [`async_hooks`](https://nodejs.org/docs/latest-v22.x/api/async_hooks.html) events have a unique `asyncId` and a special `triggerId` `triggerAsyncId` property.
* `node.bootstrap`: Enables capture of Node.js bootstrap milestones.
* `node.console`: Enables capture of `console.time()` and `console.count()` output.
* `node.threadpoolwork.sync`: Enables capture of trace data for threadpool synchronous operations, such as `blob`, `zlib`, `crypto` and `node_api`.
* `node.threadpoolwork.async`: Enables capture of trace data for threadpool asynchronous operations, such as `blob`, `zlib`, `crypto` and `node_api`.
* `node.dns.native`: Enables capture of trace data for DNS queries.
* `node.net.native`: Enables capture of trace data for network.
* `node.environment`: Enables capture of Node.js Environment milestones.
* `node.fs.sync`: Enables capture of trace data for file system sync methods.
* `node.fs_dir.sync`: Enables capture of trace data for file system sync directory methods.
* `node.fs.async`: Enables capture of trace data for file system async methods.
* `node.fs_dir.async`: Enables capture of trace data for file system async directory methods.
* `node.perf`: Enables capture of [Performance API](https://nodejs.org/docs/latest-v22.x/api/perf_hooks.html) measurements.
* `node.perf.usertiming`: Enables capture of only Performance API User Timing
measures and marks.
* `node.perf.timerify`: Enables capture of only Performance API timerify
measurements.
* `node.promises.rejections`: Enables capture of trace data tracking the number
of unhandled Promise rejections and handled-after-rejections.
* `node.vm.script`: Enables capture of trace data for the `node:vm` module's `runInNewContext()`, `runInContext()`, and `runInThisContext()` methods.
* `v8`: The [V8](https://nodejs.org/docs/latest-v22.x/api/v8.html) events are GC, compiling, and execution related.
* `node.http`: Enables capture of trace data for http request / response.
By default the `node`, `node.async_hooks`, and `v8` categories are enabled.
```bash
node --trace-event-categories v8,node,node.async_hooks server.js
```
Prior versions of Node.js required the use of the `--trace-events-enabled` flag to enable trace events. This requirement has been removed. However, the `--trace-events-enabled` flag _may_ still be
used and will enable the `node`, `node.async_hooks`, and `v8` trace event categories by default.
```bash
node --trace-events-enabled
node --trace-event-categories v8,node,node.async_hooks
```
Alternatively, trace events may be enabled using the `node:trace_events` module:
```js
import trace_events from 'node:trace_events';
const tracing = trace_events.createTracing({ categories: ['node.perf'] });
tracing.enable(); // Enable trace event capture for the 'node.perf' category
// do work
tracing.disable(); // Disable trace event capture for the 'node.perf' category
```
Running Node.js with tracing enabled will produce log files that can be opened
in the [`chrome://tracing`](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool) tab of Chrome.
The logging file is by default called `node_trace.${rotation}.log`, where `${rotation}` is an incrementing log-rotation id. The filepath pattern can
be specified with `--trace-event-file-pattern` that accepts a template
string that supports `${rotation}` and `${pid}`:
```bash
node --trace-event-categories v8 --trace-event-file-pattern '${pid}-${rotation}.log' server.js
```
To guarantee that the log file is properly generated after signal events like `SIGINT`, `SIGTERM`, or `SIGBREAK`, make sure to have the appropriate handlers
in your code, such as:
```js
process.on('SIGINT', function onSigint() {
console.info('Received SIGINT.');
process.exit(130); // Or applicable exit code depending on OS and signal
});
```
The tracing system uses the same time source
as the one used by `process.hrtime()`.
However the trace-event timestamps are expressed in microseconds,
unlike `process.hrtime()` which returns nanoseconds.
The features from this module are not available in [`Worker`](https://nodejs.org/docs/latest-v22.x/api/worker_threads.html#class-worker) threads.
f
createTracing
> [!WARNING] Deno compatibility
> This symbol is a non-functional stub.
Creates and returns a `Tracing` object for the given set of `categories`.
```js
import trace_events from 'node:trace_events';
const categories = ['node.perf', 'node.async_hooks'];
const tracing = trace_events.createTracing({ categories });
tracing.enable();
// do stuff
tracing.disable();
```
f
getEnabledCategories
> [!WARNING] Deno compatibility
> This symbol is a non-functional stub.
Returns a comma-separated list of all currently-enabled trace event
categories. The current set of enabled trace event categories is determined
by the _union_ of all currently-enabled `Tracing` objects and any categories
enabled using the `--trace-event-categories` flag.
Given the file `test.js` below, the command `node --trace-event-categories node.perf test.js` will print `'node.async_hooks,node.perf'` to the console.
```js
import trace_events from 'node:trace_events';
const t1 = trace_events.createTracing({ categories: ['node.async_hooks'] });
const t2 = trace_events.createTracing({ categories: ['node.perf'] });
const t3 = trace_events.createTracing({ categories: ['v8'] });
t1.enable();
t2.enable();
console.log(trace_events.getEnabledCategories());
```
I
CreateTracingOptions
> [!WARNING] Deno compatibility
> This symbol is a non-functional stub.
I
Tracing
> [!WARNING] Deno compatibility
> This symbol is a non-functional stub.
The `Tracing` object is used to enable or disable tracing for sets of
categories. Instances are created using the
`trace_events.createTracing()` method.
When created, the `Tracing` object is disabled. Calling the
`tracing.enable()` method adds the categories to the set of enabled trace
event categories. Calling `tracing.disable()` will remove the categories
from the set of enabled trace event categories.