@rushstack/rundown

Slow startup times for Node.js commands or services? Rundown can invoke a Node.js process and:

1. View imported files: Intercept all require() calls and show which paths were loaded.
2. Find culprits: Show the chain for require() calls for each import, explaining why it was imported.
3. Detect regressions over time: Generate a concise "snapshot" report that can be committed to Git. Changes to this file may indicate potential performance regressions.

Installation

You can install this tool globally:

$ npm install --global @rushstack/rundown

# View command line help
$ rundown --help

If you will generate rundown snapshots during your build, it is recommended to install via devDependencies:

$ cd my-tool
$ npm install @rushstack/rundown --save-dev

Viewing imported files

Suppose you maintain a small NPM project that is invoked as follows:

# The folder where your tool is developed
$ cd my-tool

# When you invoke "my-tool --my-option 123 --verbose" from the shell, let's suppose that it invokes
# this Node.js command:
$ node lib/start.js --my-option 123 --verbose

And suppose that your tool's startup time is rather slow, because the code calls require() to load many different NPM packages. We can create a report to see all the imports:

# We use "--args" to pass the command-line arguments for "my-tool"
$ rundown inspect --script lib/start.js --args="--my-option 123 --verbose"

The report may look like this:

rundown-inspect.log

/path/to/my-tool/lib/start.js
/path/to/my-tool/node_modules/at-least-node/index.js
/path/to/my-tool/node_modules/fs-extra/lib/copy-sync/copy-sync.js
/path/to/my-tool/node_modules/fs-extra/lib/copy-sync/index.js
/path/to/my-tool/node_modules/fs-extra/lib/copy/copy.js
/path/to/my-tool/node_modules/fs-extra/lib/copy/index.js
/path/to/my-tool/node_modules/fs-extra/lib/empty/index.js
/path/to/my-tool/node_modules/fs-extra/lib/ensure/file.js
/path/to/my-tool/node_modules/fs-extra/lib/ensure/index.js
/path/to/my-tool/node_modules/fs-extra/lib/ensure/link.js
/path/to/my-tool/node_modules/fs-extra/lib/ensure/symlink-paths.js
/path/to/my-tool/node_modules/fs-extra/lib/ensure/symlink-type.js
/path/to/my-tool/node_modules/fs-extra/lib/ensure/symlink.js
/path/to/my-tool/node_modules/fs-extra/lib/fs/index.js
/path/to/my-tool/node_modules/fs-extra/lib/index.js
/path/to/my-tool/node_modules/fs-extra/lib/json/jsonfile.js
/path/to/my-tool/node_modules/fs-extra/lib/json/output-json-sync.js
/path/to/my-tool/node_modules/fs-extra/lib/json/output-json.js
/path/to/my-tool/node_modules/fs-extra/lib/mkdirs/index.js
/path/to/my-tool/node_modules/fs-extra/lib/mkdirs/make-dir.js
/path/to/my-tool/node_modules/fs-extra/lib/move-sync/index.js
/path/to/my-tool/node_modules/fs-extra/lib/move-sync/move-sync.js
/path/to/my-tool/node_modules/fs-extra/lib/move/index.js
/path/to/my-tool/node_modules/fs-extra/lib/move/move.js
/path/to/my-tool/node_modules/fs-extra/lib/output/index.js
/path/to/my-tool/node_modules/fs-extra/lib/path-exists/index.js
/path/to/my-tool/node_modules/fs-extra/lib/remove/index.js
/path/to/my-tool/node_modules/fs-extra/lib/remove/rimraf.js
/path/to/my-tool/node_modules/fs-extra/lib/util/stat.js
/path/to/my-tool/node_modules/fs-extra/lib/util/utimes.js
/path/to/my-tool/node_modules/graceful-fs/clone.js
/path/to/my-tool/node_modules/graceful-fs/graceful-fs.js
/path/to/my-tool/node_modules/graceful-fs/legacy-streams.js
/path/to/my-tool/node_modules/graceful-fs/polyfills.js
/path/to/my-tool/node_modules/jsonfile/index.js
/path/to/my-tool/node_modules/jsonfile/utils.js
/path/to/my-tool/node_modules/universalify/index.js

Finding callers

To see how each file is imported, you can add the --trace-imports switch.

# We use "--args" to pass the command-line arguments for "my-tool"
$ rundown inspect --script lib/start.js --args="--my-option 123 --verbose" --trace-imports

The report now shows more detail:

rundown-inspect.log

. . .
/path/to/my-tool/node_modules/graceful-fs/legacy-streams.js
  imported by /path/to/my-tool/node_modules/graceful-fs/graceful-fs.js
  imported by /path/to/my-tool/node_modules/fs-extra/lib/fs/index.js
  imported by /path/to/my-tool/node_modules/fs-extra/lib/index.js
  imported by /path/to/my-tool/lib/start.js
  imported by /rundown/lib/launcher.js

/path/to/my-tool/node_modules/graceful-fs/polyfills.js
  imported by /path/to/my-tool/node_modules/graceful-fs/graceful-fs.js
  imported by /path/to/my-tool/node_modules/fs-extra/lib/fs/index.js
  imported by /path/to/my-tool/node_modules/fs-extra/lib/index.js
  imported by /path/to/my-tool/lib/start.js
  imported by rundown/lib/launcher.js
. . .

Fixing problems

It may be the case that many of these imports are not actually used. You can avoid preloading them by converting them to lazy imports using the Import.lazy() from @rushstack/node-core-library or import-lazy.

Generating a snapshot

To detect future regressions, use the rundown snapshot command to write a snapshot file:

# We use "--args" to pass the command-line arguments for "my-tool"
$ rundown snapshot --script lib/start.js --args="--my-option 123 --verbose"

# This file can be committed to Git to track regressions
$ git add rundown-snapshot.log

The snapshot file format eliminates spurious diffs, by showing only the names of the imported packages. For local projects in a monorepo, it will show relative paths. Example output:

rundown-snapshot.log

../path/to/monorepo-sibling
at-least-node
fs-extra
graceful-fs
jsonfile
universalify

Command-line reference

usage: rundown [-h] <command> ...

Detect load time regressions by running an app, tracing require() calls, and
generating a deterministic report

Positional arguments:
  <command>
    snapshot  Invoke a Node.js script and generate a test snapshot
    inspect   Invoke a Node.js script and generate detailed diagnostic output

Optional arguments:
  -h, --help  Show this help message and exit.

For detailed help about a specific command, use: rundown <command> -h

usage: rundown snapshot [-h] -s PATH [-a STRING] [-q] [-i]

Invoke a Node.js script and generate a test snapshot. This command creates a
concise report that can be added to Git, so that its diff can be used to
detect performance regressions

Optional arguments:
  -h, --help            Show this help message and exit.
  -s PATH, --script PATH
                        The path to a .js file that will be the entry point
                        for the target Node.js process
  -a STRING, --args STRING
                        Specifies command-line arguments to be passed to the
                        target Node.js process. The value should be a single
                        text string delimited by spaces. Example: rundown
                        inspect --scripts ./example.js --args="--flag
                        --option=123"
  -q, --quiet           Suppress STDOUT/STDERR for the target Node.js process
  -i, --ignore-exit-code
                        Do not report an error if the target Node.js process
                        returns a nonzero exit code

usage: rundown inspect [-h] -s PATH [-a STRING] [-q] [-i] [-t]

Invoke a Node.js script and generate detailed diagnostic output. This command
is used to inspect performance regressions.

Optional arguments:
  -h, --help            Show this help message and exit.
  -s PATH, --script PATH
                        The path to a .js file that will be the entry point
                        for the target Node.js process
  -a STRING, --args STRING
                        Specifies command-line arguments to be passed to the
                        target Node.js process. The value should be a single
                        text string delimited by spaces. Example: rundown
                        inspect --scripts ./example.js --args="--flag
                        --option=123"
  -q, --quiet           Suppress STDOUT/STDERR for the target Node.js process
  -i, --ignore-exit-code
                        Do not report an error if the target Node.js process
                        returns a nonzero exit code
  -t, --trace-imports   Reports the call chain for each module path, showing
                        how it was imported

Links

• CHANGELOG.md - Find out what's new in the latest version

Rundown is part of the Rush Stack family of projects.