perf: use lite web animations polyfill (#1011)

package.json

@@ -99,7 +99,6 @@
     "terser-webpack-plugin": "^1.2.2",
     "text-encoding": "^0.7.0",
     "tiny-queue": "^0.2.1",
-    "web-animations-js": "^2.3.1",
     "webpack": "^4.29.3",
     "webpack-bundle-analyzer": "^3.0.4"
   },

src/routes/_components/IconButton.html

@@ -107,6 +107,7 @@
 <script>
   import { classname } from '../_utils/classname'
   import { store } from '../_store/store'
+  import { animate } from '../_utils/animate'
 
   export default {
     data: () => ({
@@ -143,8 +144,7 @@
           return
         }
         let svg = this.refs.svg
-        let animations = animation.map(({ properties, options }) => svg.animate(properties, options))
-        animations.forEach(anim => anim.play())
+        animate(svg, animation)
       }
     }
   }

src/routes/_utils/animate.js

@@ -0,0 +1,59 @@
+// Lightweight polyfill for web animations API element.animate()
+// This is good enough for my use case, although not a full polyfill
+// of the entire API
+
+// via https://stackoverflow.com/a/15710692
+function hashCode (s) {
+  return s.split('')
+    .reduce((a, b) => {
+      a = ((a << 5) - a) + b.charCodeAt(0)
+      return a & a
+    }, 0)
+}
+
+function generateCss (id, animations) {
+  let keyframes = animations.map(({ properties }, i) => (
+    `@keyframes keyframe-${id}-${i} {
+      ${properties.map((obj, i) => (`${Math.round(100 * i / (properties.length - 1))}% {
+          ${Object.keys(obj).map(key => `${key}: ${obj[key]};`).join('')}
+        }`
+    )).join('')}
+    }`
+  ))
+
+  let animationCss = `.${id} {
+    animation: ${animations.map(({ options }, i) => {
+    return `keyframe-${id}-${i} ${options.duration}ms ${options.easing}`
+  }).join(',')};
+  }`
+
+  return keyframes + animationCss
+}
+
+export function animate (el, animations) {
+  if (typeof el.animate === 'function') {
+    return animations
+      .map(({ properties, options }) => el.animate(properties, options))
+      .map(anim => anim.play())
+  }
+
+  let hash = hashCode(JSON.stringify(animations))
+  let id = `anim-${hash}`
+
+  if (!document.getElementById(id)) {
+    let style = document.createElement('style')
+    style.id = id
+    style.textContent = generateCss(id, animations)
+    document.head.appendChild(style)
+  }
+
+  requestAnimationFrame(() => {
+    el.classList.add(id)
+    let wait = Math.max.apply(Math, animations.map(({ options }) => options.duration))
+    setTimeout(() => {
+      requestAnimationFrame(() => {
+        el.classList.remove(id)
+      })
+    }, wait)
+  })
+}

src/routes/_utils/asyncPolyfills.js

@@ -6,10 +6,6 @@ export const importRequestIdleCallback = () => import(
   /* webpackChunkName: '$polyfill$-requestidlecallback' */ 'requestidlecallback'
   )
 
-export const importWebAnimationPolyfill = () => import(
-  /* webpackChunkName: '$polyfill$-web-animations-js' */ 'web-animations-js'
-  )
-
 export const importIndexedDBGetAllShim = () => import(
   /* webpackChunkName: '$polyfill$-indexeddb-getall-shim' */ 'indexeddb-getall-shim'
   )

src/routes/_utils/loadPolyfills.js

@@ -2,15 +2,13 @@ import {
   importCustomElementsPolyfill,
   importIndexedDBGetAllShim,
   importIntersectionObserver,
-  importRequestIdleCallback,
-  importWebAnimationPolyfill
+  importRequestIdleCallback
 } from './asyncPolyfills'
 
 export function loadPolyfills () {
   return Promise.all([
     typeof IntersectionObserver === 'undefined' && importIntersectionObserver(),
     typeof requestIdleCallback === 'undefined' && importRequestIdleCallback(),
-    !Element.prototype.animate && importWebAnimationPolyfill(),
     !IDBObjectStore.prototype.getAll && importIndexedDBGetAllShim(),
     typeof customElements === 'undefined' && importCustomElementsPolyfill()
   ])

yarn.lock

@@ -7754,11 +7754,6 @@ watchpack@^1.5.0:
     graceful-fs "^4.1.2"
     neo-async "^2.5.0"
 
-web-animations-js@^2.3.1:
-  version "2.3.1"
-  resolved "https://registry.yarnpkg.com/web-animations-js/-/web-animations-js-2.3.1.tgz#3a6d9bc15196377a90f8e2803fa5262165b04510"
-  integrity sha1-Om2bwVGWN3qQ+OKAP6UmIWWwRRA=
-
 webauth@^1.1.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/webauth/-/webauth-1.1.0.tgz#64704f6b8026986605bc3ca629952e6e26fdd100"