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Web Performance 101 [Chrome Dev Summit 2021]

Web Performance 101 [Chrome Dev Summit 2021]

What do we mean when we talk about "web performance"? Why should you care about it? How can measure it? How do you get other people in your organization to care? In this workshop at the 2021 Chrome Dev Summit, I covered these questions – including an overview of the history of performance metrics, up to Core Web Vitals.

Tammy Everts

November 09, 2021

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  1. Web Performance 101 What is web performance and why should

    I care? @tameverts #ChromeDevSummit ¯\_(ツ)_/¯
  2. What is “web performance”? Why should I care about it?

    How do I measure it? How can I get other people in my company to care about it?
  3. People in rural areas People in Indigenous communities People with

    lower incomes Children Seniors People with accessibility challenges People in developing countries
  4. 1 out of 3 homes in the US do not

    have broadband access. (25 Mbps down and 3 Mbps up) Federal Communications Commission, 2020 @tameverts
  5. “I grew up with our community being under constant boil

    water advisories, and I wasn’t able to safely drink water out of the tap until just a few years ago. High-speed internet feels equally life changing.” Chief Willie Sellars, 2020
  6. Page jank affects people with motor skill challenges (esp. on

    mobile). Assistive technology (e.g., screenreaders) may not work until the DOM fully loads. JavaScript can block assistive tech. @marcysutton
  7. Users aged 65 and older are 43% slower at using

    websites than users aged 21-55. nngroup.com/articles/usability-for-senior-citizens/ @tameverts
  8. The average web user believes they waste two days a

    year waiting for pages to load.
  9. 37 “We want you to be able to flick from

    one page to another as quickly as you can flick a page on a book. So, we’re really aiming very, very high here… at something like 100 milliseconds.” Urs Hölzle SVP Engineering, Google
  10. “web stress” When apps or sites are slow, we have

    to concentrate up to 50% harder to stay on task. @tameverts
  11. ❑ bounce rate ❑ cart size ❑ conversions ❑ revenue

    ❑ time on site ❑ page views ❑ SEO ❑ brand perception ❑ user retention ❑ competitors
  12. Every 1 second of load time improvement equaled a 2%

    conversion rate increase for Walmart Staples shaved 1 second from median load time, improved conversion rate by 10% Fanatics cut median load times by 2 seconds, almost doubled mobile conversions
  13. SEO

  14. Good pages rank slightly (1%) better than average. Slow pages

    rank significantly (3.7%) worse. sistrix.com/blog/core-web-vitals-is-a-measurable-ranking-factor/
  15. Threshold YOU create for metrics that are meaningful for YOUR

    site Milestone timings (e.g. Start Render) Quantity-based (e.g. image weight) Rules-based (e.g. Lighthouse scores)
  16. A good performance budget should show you… What your budget

    is When you go out of bounds How long you’re out of bounds When you’re back within budget
  17. 2009 Improved average load time from 6s à 1.2s 7-12%

    increase in conversion rate + 25% increase in PVs Average load time degraded to 5s User feedback: “I will not come back to this site again.” Re-focused on performance 0.4% increase in conversion rate 2010 2011 @tameverts
  18. 1. No front-end measurement 2. Constant feature development 3. Badly

    implemented third-parties 4. Waited too long to tackle problems 5. Relied on performance sprints 6. No way to track regressions
  19. 1. Which metrics should I focus on? 2. What should

    my budget thresholds be? 3. How do I stay on top of them?
  20. What tools can we use? Synthetic (lab) Consistent baseline Mimics

    network & browser conditions No installation Compare any sites Detailed analysis Waterfall charts Filmstrips and videos Limited URLs Real user monitoring (field) Requires JavaScript installation Large sample size (up to 100%) Real network & browser conditions Geographic spread Correlation with other metrics (bounce rate) No detailed analysis Only measure your own site
  21. Start Render The time from the start of the initial

    navigation until the first non-white content is painted Synthetic & RUM
  22. Score that reflects how much page elements shift during rendering.

    Available in Chrome and Chromium-based browsers. Synthetic & RUM
  23. Amount of time it takes for page to respond to

    user input (e.g. click, tap, key) Only measurable via RUM
  24. FID can seem fast because user interactions take place later

    in the page’s rendering cycle... after CPU-hogging long tasks have completed. speedcurve.com/blog/first-input-delay-google-core-web-vitals/
  25. Long Tasks Measures JavaScript functions that take 50ms or longer.

    Long or excessive JS tasks can delay rendering, as well as cause page “jank”. Measurable across browser types. Synthetic & RUM
  26. Custom metrics Measure performance with high-precision timestamps Synthetic & RUM

    https://www.w3.org/TR/user-timing/ https://speedcurve.com/blog/user-timing-and-custom-metrics/
  27. Time to First Tweet The time from clicking the link

    to viewing the first tweet on each page’s timeline Pinner Wait Time (PWT) The time from initiating an action (e.g., tapping a pin) until the action is complete (pin close-up view is loaded) Time to Interact (TTI)
  28. Lighthouse Scores based on audits run on synthetic tests. Checks

    your page against “rules” for Performance, PWA, Best Practices, and SEO. For each category, you get a score out of 100 and recommendations for what to fix. developers.google.com/web/tools/lighthouse
  29. Goals are aspirational. How fast do I want to be

    eventually? Budgets are pragmatic. How can I keep my site from getting slower while I work toward my goals?
  30. “The largest hurdle to creating and maintaining stellar site performance

    is the culture of your organization. Lara Hogan designingforperformance.com
  31. “No matter the size or type of team, it can

    be a challenge to educate, incentivize, and empower those around you. “Performance more often comes down to a cultural challenge, rather than simply a technical one.” Lara Hogan designingforperformance.com
  32. Embrace performance from the ground up. Embed engineers into other

    teams. Enlist performance ambassadors. Teach people how to use (or at least understand) the monitoring tools you use.
  33. We first went to the engineering leaders, and then we

    went to our product leader. Our pitch was totally different... Reefath Rajali // PayPal chasingwaterfalls.io/episodes/episode-two-with-reefath-rajali/
  34. “When we went to our product leaders, we spoke more

    about the business numbers and the business benefits. “When we spoke to our engineering leaders, it was more about our consumer delight.” Reefath Rajali // PayPal chasingwaterfalls.io/episodes/episode-two-with-reefath-rajali/
  35. ❑ bounce rate ❑ cart size ❑ conversions ❑ revenue

    ❑ time on site ❑ page views ❑ SEO ❑ user happiness ❑ user retention ❑ competitors
  36. Who they are What they care about What to show

    them Executives Competition Business impact Benchmarks (filmstrips and videos) Correlation charts (perf + KPIs) Marketing Third parties Traffic + engagement SEO Content Third-party performance Correlation charts (perf + bounce rate) Lighthouse SEO audits Image size Devs / engineers Well, lots of stuff, probably Consult with perf team @tameverts
  37. “One of the original directives of the performance team was

    we weren’t going to set ourselves up to be performance cops.” Dan Chilton, Vox Media responsivewebdesign.com/podcast/vox-media-performance/
  38. “We weren’t going to go around slapping people on the

    wrist, saying, ‘You built an article that broke the page size budget! You have to take that down or change that immediately!’ “Our goal setting out was to set up best practices, make recommendations, and be a resource within the company that people can turn to when they have to make performance- related decisions.” Dan Chilton, Vox Media responsivewebdesign.com/podcast/vox-media-performance/
  39. “We, as engineers, should learn how to show the impact

    on anything we do.” Malek Hakim // Priceline chasingwaterfalls.io/episodes/episode-one-with-malek-hakim/
  40. “The dull boring stuff” ~Andy Davies Scripts (especially third parties)

    Images Extraneous code Defer assets where possible
  41. !!!

  42. There’s no magic. Show up with a plan. Do the

    work. Always be measuring. Keep doing the work. (Be patient.)