The Browser Hacker's Guide To Instant Loading

The web has lacked a predictable story for loading content efficiently in a way that gets you interactive in just a few seconds. Developers have a number of primitives to get there: preload, preconnect, prefetch, HTTP/2 server push, module loading, service workers. . .the list goes on. Yet the interaction between these different pieces of the web is still not well understood or explained.

So how do you preload content that is still going to be there when a user closes the tab and comes back to visit another time? How do you avoid keeping the main thread pegged with too much JavaScript? How much is too much to ship down the wire? Venture deep into the belly of the browser to uncover the secret to instantly loading anything—backed by data.

Addy Osmani shares data-driven techniques and performance patterns for efficiently loading content instantly and explains how to ship JavaScript bundles on mobile that don’t break the bank.

Presented twice at Fluent/Velocity 2017

Transcript

1. View Slide

2. loading is a user journey
   with many disparate expectations
   you’ve probably heard to REDUCE DNS LOOKUPS, REDUCE ROUND-TRIP TIMES, MINIMIZE REDIRECTS, ELIMINATE UNN
   

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4. USERS LOOK FOR VISUAL FEEDBACK TO reassure
   them everything is working as expected.
   

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5. first Interactive
   consistently Interactive
   

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6. Time to Interactive
   <5s
   on an average mobile
   device over 3G
   *2s on repeat-load a:er Service Worker registered
   GOAL
   

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7. 19s
   16s 420KB
   JavaScript Startup Performance, Double-Click Mobile Speed Matters report & the HTTP Archive
   The average web page on mobile in 2017
   UNTIL INTERACTIVE FULLY LOADED JAVASCRIPT
   

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11. PERFORMANCE
    JavaScript
    Start-up Start-up
    o o
    V8 Runtime Call Stats
    

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12. 1MB script
    (250KB minified)
    JS Parse Time On Mobile
    

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14. about:inspect in Chrome DevTools
    

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16. webpagetest.org/easy
    Moto G4 + 3G
    

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18. Code-splitting
    // Defines a “split-point” for a separate bundle
    require.ensure([], () => {
    const profile = require('./UserProfile', cb);
    });
    import('./UserProfile')
    .then(loadRoute(cb))
    .catch(errorLoading)
    Webpack 2+
    Webpack 1
    Also see Splittable, Closure Compiler
    or Browserify
    

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19. Do I need to split?
    Try Code Coverage
    in Chrome DevTools
    

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20. Tree-shaking
    // app.js
    import { a } from ‘./module.js’;
    // module.js
    export function a () {}
    export function b () {}
    ❌
    

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21. Use babel-preset-env to only transpile code for browsers that need it
    {
    "presets": [
    ["env", {
    "targets": {
    "browsers": ["last 2 versions"]
    }
    }]
    ]
    }
    Only transpile what you need with
    

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22. workflow
    

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23. Minify _everything_
    Babelified ES5 w/Uglify
    ES2015+ with Babili
    css-loader + minimize:true
    Code-splitting
    Dynamic import()
    Route-based chunking
    Tree-shaking
    Webpack 2+ with Uglify
    RollUp
    DCE w/ Closure Compiler
    Optimize “Vendor” libs
    NODE_ENV=production
    CommonsChunk + HashedModuleIdsPlugin()
    Transpile less code
    babel-preset-env + modules:false
    Browserlist
    useBuiltIns: true
    Scope Hoisting:
    Webpack 3
    RollUp
    Strip unused Lodash modules
    lodash-webpack-plugin
    babel-plugin-lodash
    Fewer Moment.js locales
    ContextReplacementPlugin()
    

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25. Plenty of lightweight options for mobile
    Lower total cost on size + parse times from the get-go
    

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28. Byte savings @
    

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29. Brotli
    Display Ads from Google now served
    using Brotli compression!
    40%
    Data-savings up to
    15% in aggregate over gzip
    https://developers.googleblog.com/
    

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30. Brotli
    Improved load time by 7% in India & 4% U.S
    bit.ly/linkedin-brotli
    Decreased the size of static assets by 20%
    bit.ly/dropbox-brotli
    17% improvement for largest JS bundles
    bit.ly/certsimple-brotli
    1.5 petabytes (million gigs) saved a day
    bit.ly/playstore-brotli
    

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31. WebP
    30% smaller than JPEG
    25% smaller than PNG
    

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32. WebP
    bit.ly/webp-format
    Serving over 43B image requests a day
    25-30%
    savings for WebP on average (26% lossless)
    Data Saver + Web Store
    

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33. WebP Conversion
    XNConvert
    Windows/Mac/Linux
    Can convert in batch
    Supports most formats
    Alternatively:
    imagemin
    Pixelmator
    ImageMagick
    GIMP
    Leptonica
    

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34. WebP Serving
    
    
    
    
    
    
    
    
    
    
    Or use the Accept header + .htaccess to serve WebP if a browser supports it and it exists on disk.
    

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35. Service Workers
    Inbox by Gmail
    10%
    improvement in Time-to-Interactive
    

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37. HTTP Caching Checklist
    Use consistent URLs and minimize resource churn
    Provide a validation token (ETag) to avoid transferring unchanged bytes
    Identify resources that can be cached by intermediaries (like CDNs)
    Determine the optimal cache lifetime of resources (max-age)
    Consider a Service Worker for more control over your repeat visit caching
    1.
    2.
    3.
    4.
    5.
    bit.ly/caching-checklist
    

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39. Let’s hack
    

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40. ResourceLoadPriorityVeryHigh
    

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43. ResourceLoadPriorityVeryHigh
    

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44. FLUENTinium
    

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45. Original
    Everything is high priority
    Preloaded JS
    Preloaded CSS + fonts
    

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46. Original
    Everything is high priority
    JS + CSS is high priority
    CSS + fonts are high prio
    

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52. 
    
    
    
    ..
    Link: 1.js; rel="preload"; as="script"
    
    

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57. bit.ly/prpl-paFern
    PRPL
    bit.ly/prpl-paFern
    

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58. HTTP/2 with 3G
    

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59. HTTP/2 + preload with 3G
    

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62. Express + HTTP/2 Push Headers
    const express = require('express'),
    let app = express();
    app
    .use('/js', express.static('js'))
    .get('/', function (req, res) {
    res.set('Link', `
    ; rel=preload; as='style',
    ; rel=preload; as='script',
    ; rel=preload; as='script'`)
    

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66. Alternatively: Track cache content using cookies
    if (supports_http2() && !http_cached('/app.js')) {
    header('link:; rel=preload; as=script’);
    setcookie('/app.js', 'is-cached', 0, '/');
    }
    

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67. Alternatively: Track cache content using cookies
    function http_cached($filename) {
    if ('is-cached' === $_COOKIE[$filename]) {
    return true;
    } else {
    return false;
    }
    }
    Try CASPer
    

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69. Repeat visit with Service Worker
    

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70. Next: Differential Serving based on
    browser compatibility?
    HTTP/1 works better when resources are concatenated (bundled)
    HTTP/2 works better when resources are more granular (unbundled)
    Serve an unbundled build for server/browser combinations supporting
    HTTP/2. Trigger delivery with or HTTP/2 Push
    Serve a bundled build to minimize round-trips to get the app running on
    server/browser combinations that don't support HTTP/2 Push
    

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71. Debugging: HTTP/2 Server Push in DevTools
    

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72. Debugging: HTTP/2 Server Push in DevTools
    

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73. HTTP/2 Server Push Rules Of Thumb
    Push just enough resources to fill idle network time, and no more.
    Push resources in evaluation-dependence order.
    Consider using strategies to track the client-side cache.
    Use the right cookies when pushing resources.
    Use server push to fill the initial cwnd. Consider
    preload links to reveal remaining critical resources.
    1.
    2.
    3.
    4.
    5.
    bit.ly/h2push
    PUSH
    

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75. PRPL In-A-Box
    Polymer App
    Toolbox
    PREACT
    CLI
    

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79. With Service Workers
    

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80. With HTTP/2 Server Push
    

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81. babel-preset-env + per-browser bundles
    

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82. babel-preset-env + per-browser bundles
    

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83. Twitter Lite
    

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85. Interactive in <5s on 3G
    

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86. Can we get fast 3G numbers
    across the board or regular
    3G?
    

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87. PRPL
    Push / Preload
    

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88. 18% improvement
    
    

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89. 36% improvement
    
    

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90. Render
    

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91. HTML Streaming
    reduced TTFB by 30%
    (200ms), increasing time
    user’s spent in the app.
    Nicolas Gallagher, Technical lead for Twitter Lite
    

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93. 4x improvement to
    render perf by using
    requestIdleCallback() to
    defer JS loading of
    images.
    Nicolas Gallagher, Technical lead for Twitter Lite
    

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94. Heavy image decode Lower image decode
    

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95. Adapt intelligently
    H
    E
    I
    G
    H
    T
    Size appropriately
    WIDTH
    IMAGE DECODE
    Compress carefully Take care with tools
    Prioritize critical images
    HIGH
    LOW
    Lazy-load the rest
    Choose the right format
    High-perf
    Images
    

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96. Data Saver Mode introduced up to 70% savings
    Next up: Save-Data client hint
    

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97. Precache
    

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98. This is a headline
    Followed by a subhead
    This is body copy and it goes a little like this and Lorem ipsum
    dolor sit amet, consectetur adipiscing elit. This is body copy and
    it goes a little like this and Lorem ipsum dolor sit amet,
    consectetur adipiscing elit.
    Application Shell
    A skeleton representing the
    user interface that can be
    offline cached & instantly
    rendered on repeat visits.
    

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99. Before Service Worker
    After Service Worker
    

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100. Lazy-load
     

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102. Before code-splitting
     

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103. webpack-web.config.js
     const plugins = [
     // extract vendor and webpack's module manifest
     new webpack.optimize.CommonsChunkPlugin({
     names: [ 'vendor', 'manifest' ],
     minChunks: Infinity
     }),
     // extract common modules from all the chunks (requires no
     'name' property)
     new webpack.optimize.CommonsChunkPlugin({
     async: true,
     children: true,
     minChunks: 4
     })
     ];
     

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104. After code-splitting
     bit.ly/twitterlite-perf
     bit.ly/twitter-casestudy
     

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107. https://meowni.ca/font-style-matcher/
     

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108. https://www.zachleat.com/web/comprehensive-webfonts/
     “Comprehensive
     Web Fonts”
     

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111. type="font/woff">
     Link: ; rel=preload; as=font;
     type='font/woff'
     

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112. Heaviest use of rel=preload is for Web Fonts
     HTTPArchive
     

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113. Preloading Web Fonts = 50% (1.2s)
     improvement in time-to-text-paint
     

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114. Control font performance
     with font-display
     auto: uses whatever font display strategy the user-agent uses
     block: draws "invisible" text at first if the font is not loaded, but swaps
     the font face in as soon as it loads
     swap: draws text immediately with a fallback if the font face isn’t
     loaded, but swaps the font face in as soon as it loads
     fallback: font face is rendered with a fallback at first if it’s not loaded,
     but the font is swapped as soon as it loads
     optional: if the font face can’t be loaded quickly, just use the fallback
     Chrome 60
     

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117. bit.ly/font-subsetting
     

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118. https://fonts.googleapis.com/css?family=Inconsolata
     https://fonts.googleapis.com/css?family=Inconsolata&text=Hello
     Web Font Subsetting
     ~3KB
     ~880 bytes
     Supported by Google Fonts
     

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119. /* Small subset, normal weight */
     @font-face {
     font-family: whatever;
     src: url('reg-subset.woff')
     format('woff');
     unicode-range: U+0-A0;
     font-weight: normal;
     }
     The browser can also handle subsetting!
     https://jakearchibald.com/2014/minimising-font-downloads/
     /* Large subset, normal weight */
     @font-face {
     font-family: whatever;
     src: url('reg-extended.woff')
     format('woff');
     unicode-range: U+A0-FFFF;
     font-weight: normal;
     }
     Chrome 36
     Firefox 44
     

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120. CSS Font Loading API
     https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/webfont-optimization
     const font = new FontFace("Awesome Font", "url(/fonts/awesome.woff2)", {
     style: 'normal', unicodeRange: 'U+000-5FF', weight: '400'
     });
     // don't wait for the render tree, initiate an immediate fetch!
     font.load().then(function() {
     // apply the font (which may re-render text and cause a page reflow)
     // after the font has finished downloading
     document.fonts.add(font);
     document.body.style.fontFamily = "Awesome Font, serif";
     // OR... apply your own render strategy here...
     });
     Chrome 35
     Firefox 41
     

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121. Web Font Loading Tips
     Understand the anatomy of a web font and how browsers load
     font-display: optional (i.e if you can’t do it fast, load a fallback)
     Minimize font downloads by limiting range of characters you’re loading
     Minimize FOIT by using
     If you need more control try out the Font Loading API
     1.
     2.
     3.
     4.
     5.
     https://meowni.ca/posts/web-fonts/
     

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123. Streams API
     bit.ly/streams-ftw
     Progressive Loading: HTML
     

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124. in body
     bit.ly/progressive-css
     Progressive Loading: CSS
     

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125. in body
     bit.ly/progressive-css
     Progressive Loading: CSS
     
     
     
     …
     
     …
     
     …
     
     …
     
     

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127. medium.com/reloading
     

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