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Performance.now() fast but not furious
- 1. Front-end Dev & Designer at Lunar Logic Anna Migas Google Developer Expert @szynszyliszys
- 2. Anna Migas @szynszyliszys Fast but not furious: Debugging user interaction performance issues
- 5. Perceived performance First Meaningful Paint Time to interactive
- 6. Optimise Critical Rendering Path
- 7. Optimise Critical Rendering Path Use progress bars instead of spinners
- 8. Optimise Critical Rendering Path Use progress bars instead of spinners Have a placeholder content
- 9. Optimise Critical Rendering Path Use progress bars instead of spinners Have a placeholder content Start upload before user even decides to click the upload button
- 12. ! "
- 17. Perceived performance First Meaningful Paint Time to interactive Smooth at all times
- 18. Agenda 1. Why sometimes interactions feel slow 2. Browser rendering and frames 3. Types of triggered changes in the UI 4. How to test for interaction performance 5. Potentially dangerous user interface patterns
- 19. J A N K
- 21. 60 fps 
 1000/60 = ~16.6ms
- 22. 60 fps 
 1000/60 = ~16.6ms 120 fps 
 1000/120 = ~8.3ms iPad Pro, Razer smartphone
- 23. How can we help the browser to make it on time?
- 24. Offload the main thread main thread (UI)
- 25. Offload the main thread BUS main thread (UI) background thread (heavy task)
- 26. Offload the main thread 1. Use Web Workers for heavy tasks 2. Optimise the main thread
- 27. Offload the main thread 1. Use Web Workers for heavy tasks 2. Optimise the main thread
- 28. If we interact with a page, a browser needs to start serving frames (ideally 60 or 120 per second)
- 29. What a frame consists of?
- 30. What a browser does during these steps?
- 31. Change happens, an event is fired 1
- 34. Layout
- 35. Everything is rasterised and painted to the layers 4
- 36. Paint
- 37. Paint
- 38. Layers
- 39. What creates new layers? 1. 3D or perspective transforms 2. Animated 2D transforms or opacity 3. Being on top/a child of a compositing layer 4. Accelerated CSS filters 5. In special cases <video>, <canvas>, plugins 6. will-change CSS property
- 41. Every layer consumes memory. Use them wisely.
- 42. Compositing 5
- 43. Compositing
- 44. Compositing
- 45. Types of triggered changes
- 46. Layout change (Reflow) (width, margin-top, left)
- 47. Paint change (Repaint) (background-color, box-shadow, background-image)
- 49. How to test if we have a problem?
- 50. Reflows can be quite obvious…
- 51. …but for Repaints we might need better tools
- 52. Performance tab (Chrome or Firefox)
- 53. Performance tab (Chrome or Firefox)
- 58. Performance monitor tab (Chrome)
- 59. What are the potentially dangerous UI patterns?
- 60. Animations 1
- 61. Animations 1. Don’t overuse animations 2. Animate only transform and opacity if possible 3. Use requestAnimationFrame()
- 62. requestAnimationFrame function repeated() { // show something many times window.requestAnimationFrame(repeated); } window.requestAnimationFrame(repeated);
- 63. Animations 1. Don’t overuse animations 2. Animate only transform and opacity if possible 3. Use requestAnimationFrame() but… 4. …for 120fps avoid requestAnimationFrame() 5. Don’t animate elements below other nodes (like fixed headers) 6. Don’t animate too many elements
- 66. Parallax effect 1. Causes Paint Storms 2. Almost always bad 3. Don’t use scroll events 4. Don’t use background-position 5. Use 3D transforms and perspective if you need to: https://developers.google.com/web/updates/ 2016/12/performant-parallaxing
- 67. Fixed elements 3
- 69. Fixed elements 1. Repaints with every frame when scrolling 2. Use will-change property (or transform: translate3D(0,0,0)) to avoid repainting .fixed-element { position: fixed; will-change: transform; }
- 71. Scrolling events 1. Don’t attach wheel or touch listeners to the whole document, use smaller areas instead 2. Take advantage of passive event listeners (use with polyfill): window.addEventListener("scroll", func, {passive: true});
- 72. Hover effects 5
- 74. Hover effects 1. If they are bound to happen often—you might consider using will-change property 2. Can be deadly if there are too many and can be easily triggered 3. Avoid effects triggering Layout or Paint: https://csstriggers.com/
- 77. Appending elements 1. Make sure not many elements will be affected 2. Try to separate the area (will-change, contain: layout) 3. Try not to change the size of area (for example use overflow property)
- 78. Images 7
- 79. https://unsplash.com/ (on slow 3G)
- 80. Images A. Can be downloaded in unexpected ways B. Can cause content jumps on load C. Lazy loading is tricky
- 82. Images: downloads • Semantics = performance • How image is embedded (img tag/background- image) influences the time of download • Comprehensive research by Harry Roberts
- 83. Images: downloads (img tag) <img src=“image.png” alt=“Alt text”>
- 84. Images: downloads (background img) background-image: url(“image.png”);
- 87. Images: content jumps • No jumps in Chrome any more (scroll anchoring enabled by default in Chrome 56) • Can be avoided by using a placeholder content eg. created with the intristic ratio: (img-height / img-width) * 100% .container { padding-bottom: $intristic-ratio; height: 0; overflow: hidden; }
- 90. Images: lazy loading • There are situations when it can make the experience worse because of reflows • https://jobs.zalando.com/tech/blog/loading- time-matters/index.html • Placeholders can be a solution (eg. Low Quality Placeholders)
- 91. Takeaways 1. Jank happens when the browser doesn’t finish rendering a frame on time 2. Try to offload and optimise the main thread 3. Avoid content Reflows and Repaints 4. Don’t overuse layers 5. Test your website with Performance, Layers and Rendering tabs 6. Use responsibly potentially dangerous UI patterns
- 92. Resources 1. http://jankfree.org 2. https://dev.opera.com/articles/css-will-change-property 3. https://www.udacity.com/course/browser-rendering-optimization--ud860 4. https://www.html5rocks.com/en/tutorials/speed/layers 5. https://www.html5rocks.com/en/tutorials/speed/high-performance- animations 6. https://blog.logrocket.com/eliminate-content-repaints-with-the-new-layers- panel-in-chrome-e2c306d4d752 7.https://dassur.ma/things/120fps 8. https://developers.google.com/web/tools/chrome-devtools/speed/get- started