bench-node

The bench-node module allows you to measure operations per second of Node.js code blocks.

Install

$ npm install bench-node

Usage

const { Suite } = require('bench-node');

const suite = new Suite();

suite.add('Using delete property', () => {
  const data = { x: 1, y: 2, z: 3 };
  delete data.y;

  data.x;
  data.y;
  data.z;
});

suite.run()

$ node --allow-natives-syntax my-benchmark.js
Using delete property x 3,326,913 ops/sec (11 runs sampled) v8-never-optimize=true min..max=(0ns ... 0ns) p75=0ns p99=0ns

This module uses V8 deoptimization to help ensure that the code block is not optimized away, producing accurate benchmarks -- but not realistic. See the Writing JavaScript Microbenchmark Mistakes section for more details.

The bench-node-cli tool allows you to execute a bench-node benchmark from any location, eliminating the need to install the bench-node package locally. Simply use the following command to run your benchmark:

npx bench-node-cli my-benchmark.js

See the examples folder for more common usage examples.

Table of Contents

1. Class Suite
   1. suite.add()
   2. suite.run()
2. Plugins
3. Using Reporter
   1. Text Reporter
   2. Chart Reporter
   3. Custom Reporter
4. Setup and Teardown
   1. Managed Benchmarks

Class: Suite

Stability: 1.1 Active Development

A Suite manages and executes benchmark functions. It provides two methods: add() and run().

new Suite([options])

• options {Object} Configuration options for the suite.
  • reporter {Function} Callback function for reporting results. Receives one argument:
    • results {Object[]} Array of benchmark results:
      • name {string} Benchmark name.
      • opsSec {string} Operations per second.
      • iterations {Number} Number of iterations.
      • histogram {Histogram} Histogram instance.

If no reporter is provided, results are printed to the console.

const { Suite } = require('bench-node');
const suite = new Suite();

If you don't want results to be printed to the console, false and null can be used

const { Suite } = require('bench-node');
const suite = new Suite({ reporter: false });

suite.add(name[, options], fn)

• name {string} The name of the benchmark, displayed when reporting results.
• options {Object} Configuration options for the benchmark. Supported properties:
  • minTime {number} Minimum duration for the benchmark to run. Default: 0.05 seconds.
  • maxTime {number} Maximum duration for the benchmark to run. Default: 0.5 seconds.
• fn {Function|AsyncFunction} The benchmark function. Can be synchronous or asynchronous.
• Returns: {Suite}

Adds a benchmark function to the suite.

$ node --allow-natives-syntax my-benchmark.js
Using delete property x 5,853,505 ops/sec ± 0.01% (10 runs sampled) min..max=(169ns ... 171ns) p75=170ns p99=171ns

suite.run()

• Returns: {Promise<Array<Object>>} An array of benchmark results, each containing:
  • opsSec {number} Operations per second.
  • iterations {number} Number of executions of fn.
  • histogram {Histogram} Histogram of benchmark iterations.
  • name {string} Benchmark name.
  • plugins {Object} Object with plugin results if any plugins are active.

Runs all added benchmarks and returns the results.

Plugins

Plugins extend the functionality of the benchmark module.

See Plugins for details.

Plugin Methods

• isSupported(): Checks if the plugin can run in the current environment.
• beforeClockTemplate(varNames): Injects code before the benchmark starts. Returns an array with:
  • Code {string} JavaScript code to execute.
  • Wrapper {string} (optional) Function to wrap the benchmark function.
• afterClockTemplate(varNames): Injects code after the benchmark finishes. Returns an array with:
  • Code {string} JavaScript code to execute.
• onCompleteBenchmark(result): Called when the benchmark completes, allowing plugins to process results.
• toString(): Returns a string identifier for the plugin.

Example Plugin

class V8OptimizeOnNextCallPlugin {
  isSupported() {
    try {
      new Function(`%OptimizeFunctionOnNextCall(() => {})`)();
      return true;
    } catch (e) {
      return false;
    }
  }

  beforeClockTemplate({ awaitOrEmpty, bench }) {
    let code = '';
    code += `%OptimizeFunctionOnNextCall(${bench}.fn);\n`;
    code += `${awaitOrEmpty}${bench}.fn();\n`;
    code += `${awaitOrEmpty}${bench}.fn();\n`;
    return [code];
  }

  toString() {
    return 'V8OptimizeOnNextCallPlugin';
  }
}

Using Reporter

This module exports two reporters that control how benchmark results are displayed: a detailed textReport for statistical analysis, and a visual chartReport that displays a bar graph in the terminal.

textReport (Default)

The textReport is the default reporter, which provides detailed statistical information about each benchmark result. It includes the number of operations per second, the number of runs sampled, and percentile statistics (p75, p99). This format is ideal for analyzing performance with precision, allowing you to compare the efficiency of different operations at a more granular level.

Example Output:

Using delete property x 7,736,869 ops/sec (11 runs sampled) v8-never-optimize=true min..max=(127.65ns ... 129.97ns) p75=129.76ns p99=129.97ns
Using delete property (proto: null) x 23,849,066 ops/sec (11 runs sampled) v8-never-optimize=true min..max=(41.24ns ... 42.62ns) p75=42.44ns p99=42.62ns
Using undefined assignment x 114,484,354 ops/sec (11 runs sampled) v8-never-optimize=true min..max=(8.72ns ... 8.78ns) p75=8.76ns p99=8.78ns
...

Here’s how you can explicitly pass it as a reporter:

const { Suite, textReport } = require('bench-node');

const suite = new Suite({
  reporter: textReport, // Optional, since this is the default
});

chartReport

The chartReport reporter provides a graphical representation of benchmark results in the form of a bar chart, making it easier to visualize the relative performance of each benchmark. It scales the bars based on the highest operations per second (ops/sec) value, and displays the results incrementally as they are collected.

Example output:

Platform: darwin arm64
CPU Cores: 8 vCPUs | 16.0GB Mem

single with matcher                           | ██████████████████████████████ | 747215.75 ops/sec
multiple replaces                             | █████████████████████████----- | 630285.56 ops/sec

Usage:

const { Suite, chartReport } = require('bench-node');

const suite = new Suite({
  reporter: chartReport,
});

Custom Reporter

Customize data reporting by providing a reporter function when creating the Suite:

const { Suite } = require('bench-node');

function reporter(results) {
  for (const result of results) {
    console.log(`Benchmark: ${result.name}`);
    console.log(`Operations per second: ${result.opsSec}`);
    console.log(`Iterations: ${result.iterations}`);
    console.log(`Histogram: ${result.histogram}`);
  }
}

const suite = new Suite({ reporter });

suite.add('Using delete to remove property from object', () => {
  const data = { x: 1, y: 2, z: 3 };
  delete data.y;

  data.x;
  data.y;
  data.z;
});

suite.run();

$ node --allow-natives-syntax my-benchmark.js
Benchmark: Using delete to remove property from object - 6,032,212 ops/sec

Setup and Teardown

Control the benchmark function's setup and teardown using the timer argument:

const { Suite } = require('bench-node');
const { readFileSync, writeFileSync, rmSync } = require('node:fs');

const suite = new Suite();

suite.add('readFileSync', (timer) => {
  const randomFile = Date.now();
  const filePath = `./${randomFile}.txt`;
  writeFileSync(filePath, Math.random().toString());

  timer.start();
  readFileSync(filePath, 'utf8');
  timer.end();

  rmSync(filePath);
}).run();

For advanced setups, use the timer argument to start and end timing explicitly:

const { Suite } = require('bench-node');
const { readFileSync, writeFileSync, rmSync } = require('node:fs');

const suite = new Suite();

suite.add('readFileSync', (timer) => {
  const randomFile = Date.now();
  const filePath = `./${randomFile}.txt`;
  writeFileSync(filePath, Math.random().toString());

  timer.start();
  for (let i = 0; i < timer.count; i++) {
    readFileSync(filePath, 'utf8');
  }
  timer.end(timer.count);

  rmSync(filePath);
});

suite.run();

[!WARNING] When using the timer, the setup will also be deoptimized. As a result, if you compare this approach with one that uses functions outside the benchmark function, the results may not match. See: Deleting Properties Example.

Ensure you call .start() and .end() methods when using the timer argument, or an ERR_BENCHMARK_MISSING_OPERATION error will be thrown.

Managed Benchmarks

In regular benchmarks (when timer is not used), you run the benchmarked function in a loop, and the timing is managed implicitly. This means each iteration of the benchmarked function is measured directly. The downside is that optimizations like inlining or caching might affect the timing, especially for fast operations.

Example:

suite.add('Using includes', function () {
  const text = 'text/html,...';
  const r = text.includes('application/json');
});

Here, %DoNotOptimize is being called inside the loop for regular benchmarks (assuming V8NeverOptimizePlugin is being used), ensuring that the operation is not overly optimized within each loop iteration. This prevents V8 from optimizing away the operation (e.g., skipping certain steps because the result is not used or the function is too trivial).

Managed benchmarks explicitly handle timing through start() and end() calls around the benchmarked code. This encapsulates the entire set of iterations in one timed block, which can result in tighter measurement with less overhead. However, it can lead to over-optimistic results, especially if the timer’s start and stop calls are placed outside of the loop, allowing V8 to over-optimize the entire block.

Example:

suite.add('[Managed] Using includes', function (timer) {
  timer.start();
  for (let i = 0; i < timer.count; i++) {
    const text = 'text/html,...';
    const r = text.includes('application/json');
    assert.ok(r);  // Ensure the result is used so it doesn't get V8 optimized away
  }
  timer.end(timer.count);
});

In this case, %DoNotOptimize is being applied outside the loop, so it does not protect each iteration from excessive optimization. This can result in higher operation counts because V8 might optimize away repetitive tasks. That's why an assert.ok(r) has been used. To avoid V8 optimizing the entire block as the r var was not being used.

[!NOTE] V8 assumptions can change any time soon. Therefore, it's crucial to investigate results between versions of V8/Node.js.