Tony Edwards

How users perceive speed of the web – (not so) live blog

- 2 mins

This is a (not so) live blog of a talk given by Paul Irish at the O’Reilly Fluent 2015. The talk is about how users perceive speed when browsing the web and a brief look at the new chrome tools we have at our disposal. You can watch the video on YouTube as well as catch up with Paul at his website and on Twitter.

Performance, speed and user perception is a (almost) unquantifiable. Slow as a term is used to describe a variety of conditions but is a very imprecise term.

10ms. Would 10 ms affect a user on an e-commerce site? Probably not, but how about a game?

We need metrics. But which one?

  • DOMContentLoaded?
  • FPS?
  • Jank?
  • First Paint?
  • Second Visit?
  • Its important that the benchmarks are relevant to the web. Google guiding philosophy is to follow the user, everything else will follow. Therefore the question should be “What does the user feel”.

    Neilson, based on research made the following points about user perceived speed in relation to user interface.

  • 100ms – Instant response
  • 1000ms – Keeps the users flow of thought
  • 10s – Lost the users attention
  • Paul shows a video of himself browsing a website with the interaction being relatively snappy. This interaction is broken down into the four phases of user interaction.

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    User expectation is that the time between between input and paint should be as short as possible to feel immediate.

    For animations to appear fluid they need to be 60fps.

    When a page is idle, the user expects that the interface is ready for interaction, and will respond quickly.

    Load times should be short. During a load there is allot happening which can conflict with the ability of the user to interact. Once the page appears loaded is should be ready to be interacted with.

    The Chrome team call this the ‘RAIL performance model’

    [resp_image id=’367′]

    What are the target goals?

    [resp_image id=’368′]

    Paul demos some new performance tools in the latest Chrome Canary. It takes ages for the page to load and he bails on the demo.

    Dev tools’s new feature measures the RAIL performance, with the screenshots of the page captured during load. This allows devs to visualise what is holding up the interaction. Its a great way to measure the impact of an added library on page performance.

    RAIL is a work in progress and the Chrome team wants our feedback.

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