nano‐watch

nano-watch continuously benchmarks a single function, showing live statistics and memory usage.

Usage

$ npx nano-watch --help
Usage: nano-watch [options] <file> [method]

Continuously benchmark code.

Arguments:
  file                       File to benchmark.
                             If "self", prints its file name to stdout and exits
  method                     Method name to benchmark

Options:
  -V, --version              output the version number
  -m, --ms <ms>              measurement time in milliseconds (default: 500)
  -i, --iterations <number>  number of iterations (default: Infinity)
  -e, --export <name>        name of the export (default: "default")
  --self                     print the file name to stdout and exit
  -h, --help                 display help for command

• --ms — measurement time in milliseconds. Default: 500.
• --iterations — number of samples. Default: Infinity.
  • The table updates after each iteration.
  • Stop with Ctrl + C.
• --export — name of the export to use. Default: default.
• --self — print the script path and exit (for Deno, Bun, etc.).

The optional method argument selects a function from an object export (see nano-bench file format).

File format

nano-watch accepts the same file format as nano-bench.

Without method, the export must be a function:

export default n => {
  const a = 'a',
    b = 'b';
  for (let i = 0; i < n; ++i) {
    const x = a + '-' + b;
  }
};

Output

Prints a live-updating table, refreshed after each measurement (≥ --ms milliseconds).

A bounded run (--iterations) ends with an explicit process.exit(0), so a module holding live handles (servers, watchers) can't keep a finished run alive.

Example:

After calibrating the batch size (iterations per call), it displays:

• # — the iteration number.
• time — the time in milliseconds of the last iteration.
• Running statistics:
  • mean — the mean value.
  • stdDev — the standard deviation.
  • median — the median value.
  • skewness — the skewness.
  • kurtosis — the kurtosis.
    • The excess kurtosis is used.
• op/s — the number of operations per second as an alternative representation of time values (time, mean, median).
• Memory-related data obtained with process.memoryUsage():
  • Used memory in bytes (heapUsed).
  • Total memory in bytes (heapTotal).
  • Resident set size in bytes (rss) — total physical memory used by the process.

Live updates require a TTY output. If redirected to a file, only the final table is printed; use --iterations to limit the run.

Deno, Bun, etc.

Use --self to get the script path for running with alternative interpreters:

$ npx nano-watch benchmark.js concat
$ bun `npx nano-watch --self` benchmark.js concat
$ deno run --allow-read --allow-hrtime `npx nano-watch --self` benchmark.js concat
$ deno run -A `npx nano-watch --self` benchmark.js concat
$ node `npx nano-watch --self` benchmark.js concat