The Art of Lazy Loading

The magic of lazy loading images and splitting bundles ✨

1. the art of lazy loading lazy loading @hdjirdeh
2. lazy defer until the user needs it
3. loading fetch + render
4. what?
5. images!
7. highest high medium low low high highest medium low
8. highest high medium low low high highest medium low
9. low highest high medium low low high highest medium
10. highest high medium low low high highest medium medium low
11. > 40% of data fetched = images
12. scroll event listeners
13. <img class="lazy" data-src="kittens.png"> class="lazy" data-src="kittens.png"
14. let image = document.querySelector("img.lazy"); const lazyLoad = () "=> { setTimeout(() "=> { if ( image.getBoundingClientRect().top "<= window.innerHeight "&& image.getBoundingClientRect().bottom ">= 0 ) { image.src = image.dataset.src; } }, 200); }; document.addEventListener("scroll", lazyLoad); let image = document.querySelector("img.lazy"); const lazyLoad = () "=> { setTimeout(() "=> { if ( image.getBoundingClientRect().top "<= window.innerHeight "&& image.getBoundingClientRect().bottom ">= 0 ) { image.src = image.dataset.src; } }, 200); } document.addEventListener("scroll", lazyLoad); };
15. intersection observer
16. let image = document.querySelector("img.lazy"); let lazyObserver = new IntersectionObserver(entry "=> { if (entry.isIntersecting) { const image = entry.target; image.src = lazyImage.dataset.src; lazyObserver.unobserve(image); } }); lazyObserver.observe(image); let image = document.querySelector("img.lazy"); let lazyObserver = new IntersectionObserver(entry "=> { if (entry.isIntersecting) { const image = entry.target; image.src = lazyImage.dataset.src; lazyObserver.unobserve(image); } }); lazyObserver.observe(image);
17. bit.ly/inter-obs
18. native browser feature?
19. <img lazyload=“on”> lazyload=“on”
21. what else?
22. code!
24. 1 KB of Image 1 KB of JavaScript ≠
25. split, split, split ✂
26. import('lodash.sortby') .then(module "=> module.default) .then(doSomethingCool) import('lodash.sortby') .then(module "=> module.default) .then(doSomethingCool) dynamic import
27. what should I do?
28. audit
32. audit fix ✂
34. Use a library lozad.js lazysizes yall.js
35. Use IO + polyfill Use a library Use placeholders/ load early
36. Use placeholders/ load early pinterest pinterest.com
37. Use placeholders/ load early lqip-loader github.com/zouhir/lqip-loader
38. Use placeholders/ load early Primitive primitive.lol
39. Use placeholders/ load early sqip github.com/technopagan/sqip SQIP LQIP Image
41. export const routes: Routes = [ { path: 'main', component: 'MainComponent', }, { path: 'details', loadChildren: 'details/details.module#DetailsModule' } ]; angular router
42. const DetailsComponent = () "=> import(‘./details.vue'); export const router = new VueRouter({ routes: [ { path: '/details', component: DetailsComponent }, ] }) const DetailsComponent = () "=> import(‘./details.vue'); export const router = new VueRouter({ routes: [ { path: '/details', component: DetailsComponent }, ] }) const DetailsComponent = () "=> import(‘./details.vue'); export const router = new VueRouter({ routes: [ { path: '/details', component: DetailsComponent }, ] }) export const router = new VueRouter({ routes: [ { path: '/details', component: DetailsComponent }, ] }) vue router
43. import { Router } from 'preact-router'; import Home from '"../routes/home'; import Details from 'async!./details'; export const App = () "=> ( <Router> <Home path="/" "/> <Details path="/details/" "/> "</Router> ); import { Router } from 'preact-router'; import Home from '"../routes/home'; import Details from 'async!./details'; export const App = () "=> ( <Router> <Home path="/" "/> <Details path="/details/" "/> "</Router> ); preact cli import { Router } from 'preact-router'; import Home from '"../routes/home'; import Details from 'async!./details'; export const App = () "=> ( <Router> <Home path="/" "/> <Details path="/details/" "/> "</Router> );
44. const loadPage = (page) "=> (dispatch) "=> { switch(page) { case 'view1': import('"../my-view1.js').then((module) "=> { "// ""... }); break; "//""... } dispatch(updatePage(page)); }; const loadPage = (page) "=> (dispatch) "=> { switch(page) { case 'view1': import('"../my-view1.js').then((module) "=> { "// ""... }); break; "//""... } dispatch(updatePage(page)); }; const loadPage = (page) "=> (dispatch) "=> { switch(page) { case 'view1': import('"../my-view1.js').then((module) "=> { "// ""... }); break; "//""... } dispatch(updatePage(page)); }; polymer pwa-starter-kit
45. import Loadable from 'react-loadable'; const DetailsComponent = Loadable({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, }); import Loadable from 'react-loadable'; const DetailsComponent = Loadable({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, }); import Loadable from 'react-loadable'; const DetailsComponent = Loadable({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, }); jamiebuilds / react-loadable
46. import loadable from 'loadable-components'; const DetailsComponent = loadable(() "=> import('./details.component'), { LoadingComponent: () "=> <div>Loading""..."</div> }); import loadable from 'loadable-components'; const DetailsComponent = loadable(() "=> import('./details.component'), { LoadingComponent: () "=> <div>Loading""..."</div> }); import loadable from 'loadable-components'; const DetailsComponent = loadable(() "=> import('./details.component'), { LoadingComponent: () "=> <div>Loading""..."</div> }); smooth-code / loadable-components
47. import LoadableVisibility from ‘react-loadable-visibility/react-loadable' const DetailsComponent = LoadableVisibility({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, }) import LoadableVisibility from ‘react-loadable-visibility/react-loadable' const DetailsComponent = LoadableVisibility({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, }) import LoadableVisibility from ‘react-loadable-visibility/react-loadable' const DetailsComponent = LoadableVisibility({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, }) stratiformltd / react-loadable-visibility
49. const DetailsComponent = Loadable({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, delay: 300, }); jamiebuilds / react-loadable const DetailsComponent = Loadable({ loader: () "=> import('./details.component'), loading: () "=> <div>Loading""..."</div>, delay: 300, });
50. suspense
51. bit.ly/lazy-metro metro (react native)
53. audit fix ✂ observe
54. webpack-bundle-analyzer
55. size-plugin
56. progressivetooling.com
57. responsive images with srcset preload critical chunks convert gifs to .mp4 pre-cache assets using a service worker compress assets remove unused packages module / nomodule
58. / Dx Ux
59. @hdjirdeh