Performance impact

@jsenv/performance-impact analyses a pull request impact on your performance metrics. This analysis is posted in a comment of the pull request on GitHub.

• Helps you to catch big performance variations before merging a pull request
• Gives you the ability to measure performances on your machine during dev
• Can be added to any automated process (GitHub workflow, Jenkins, ...)

Disclaimer: This tool should not be used to catch small performance variations because they are hard to distinguish from the natural variations of performance metrics (see performance variability).

Pull request comment

Screenshot of a pull request comment

Performance variability

Performance metrics will change due to inherent variability, even if there hasn't been a code change. It can be mitigated by measuring performance multiple times. But you should always keep in mind this variability before drawing conclusions about a performance-impacting change.

With time you'll be capable to recognize unusual variation in your performance metrics.

How to catch small performance impacts?

Catching small to very small performance impacts with confidence requires a LOT of repetition and time. Both strategies means you will have to wait before knowing the real performance impact.

How to catch small impacts with a lot of repetition?

• Let your code be used a lot of times in a lot of scenarios and see the results. This could be scripts, real users or both.

• Push your performance metrics in a tool like Kibana or DataDog and check the tendency of your performance metrics.

In the end I would recommend the following approach:

1. measure some performance metrics
2. Use @jsenv/performance-impact to anticipate big variations
3. For small variations, upload performance metrics to a dashboard. Then, periodically watch the dashboard to check performance metrics tendency over time