lab-assistant's Introduction

lab-assistant

lab-assistant is a Puppeteer-based tool that does the grunt work of taking measurements and figuring out how much of a performance change there is between two different versions of your site.

This is a useful tool to run every time you're working on a loading performance improvement. It will help you gauge whether the improvement is real and not just placebo, and it'll give you a number to attach to your PR description, blog post, or annual employee self-assessment survey.

Impress your peers with actual numbers!

Usage

The easiest way to use lab-assistant is with a tool like npx:

npx lab-assistant http://v1.mysite.tld http://v2.mysite.tld

Here's the current full set of options (which you can get with --help):

lab-assistant.js <url> [url2]

Positionals:
  url   URL to fetch content from.
        If `url2` is not specified, this is used for both the new and old
        versions, with the application pausing in between to allow for the
        version swap.
  url2  Second URL to fetch content from.
        If specified, this refers to the new version, while `url` refers to
        the old version.

Options:
  --help              Show help                                        [boolean]
  --verbose, -v       Output more details.            [boolean] [default: false]
  --headless          Whether to use a headless browser.
                                                       [boolean] [default: true]
  --repeat, -r        The number of measurements to take for each version.
                                                          [number] [default: 10]
  --throwaway, -t     The number of throwaway visits to perform before any
                      actual measurements.
                      Keeping it at 1 or increasing the value can help with
                      stability.                           [number] [default: 1]
  --cpu_slowdown, -c  The CPU slowdown throttling to apply (may help achieve
                      more stable results in CPU-heavy pages).          [number]
  --metric, -m        The metric to consider.
                      Metrics:
                      - ttfb: Time to First Byte
                      - fp: First Paint
                      - fcp: First Contentful Paint
                      - dcl: Time to DOMContentLoad event end
                      - load: Time to Load event end
        [string] [choices: "ttfb", "fp", "fcp", "dcl", "load"] [default: "load"]