/** * 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 * * # is equivalent to * * node --trace-event-categories v8,node,node.async_hooks * ``` * * Alternatively, trace events may be enabled using the `node:trace_events` module: * * ```js * const trace_events = require('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. * @experimental * @see [source](https://github.com/nodejs/node/blob/v22.x/lib/trace_events.js) */ declare module "trace_events" { /** * 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. */ interface Tracing { /** * A comma-separated list of the trace event categories covered by this * `Tracing` object. * @since v10.0.0 */ readonly categories: string; /** * Disables this `Tracing` object. * * Only trace event categories _not_ covered by other enabled `Tracing` * objects and _not_ specified by the `--trace-event-categories` flag * will be disabled. * * ```js * const trace_events = require('node:trace_events'); * const t1 = trace_events.createTracing({ categories: ['node', 'v8'] }); * const t2 = trace_events.createTracing({ categories: ['node.perf', 'node'] }); * t1.enable(); * t2.enable(); * * // Prints 'node,node.perf,v8' * console.log(trace_events.getEnabledCategories()); * * t2.disable(); // Will only disable emission of the 'node.perf' category * * // Prints 'node,v8' * console.log(trace_events.getEnabledCategories()); * ``` * @since v10.0.0 */ disable(): void; /** * Enables this `Tracing` object for the set of categories covered by * the `Tracing` object. * @since v10.0.0 */ enable(): void; /** * `true` only if the `Tracing` object has been enabled. * @since v10.0.0 */ readonly enabled: boolean; } interface CreateTracingOptions { /** * An array of trace category names. Values included in the array are * coerced to a string when possible. An error will be thrown if the * value cannot be coerced. */ categories: string[]; } /** * Creates and returns a `Tracing` object for the given set of `categories`. * * ```js * const trace_events = require('node:trace_events'); * const categories = ['node.perf', 'node.async_hooks']; * const tracing = trace_events.createTracing({ categories }); * tracing.enable(); * // do stuff * tracing.disable(); * ``` * @since v10.0.0 */ function createTracing(options: CreateTracingOptions): Tracing; /** * 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 * const trace_events = require('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()); * ``` * @since v10.0.0 */ function getEnabledCategories(): string | undefined; } declare module "node:trace_events" { export * from "trace_events"; }