feat(global): add scroll event publish helper function

README.md

@@ -3,7 +3,7 @@
 A simple publish/subscribe pattern
 
 - Plain old vanilla JS
-- Just 1kb gzipped
+- Just 1.2kb gzipped
 
 ## Installation
 
@@ -76,6 +76,20 @@ event.subscribe('global.escape', () => {
 })
 ```
 
+#### Scroll
+
+```js
+import Event, { publishScroll } from 'core-events'
+
+const event = new Event()
+
+publishScroll({ event })
+
+event.subscribe('global.scroll', ({ direction, speed }) => {
+  console.log(`Somebody scrolled ${direction} at ${speed} px per ms`)
+})
+```
+
 #### Swipe
 
 ```js

src/index.js

@@ -1,4 +1,9 @@
-import { publishClick, publishEscape, publishSwipe } from './publish'
+import {
+  publishClick,
+  publishEscape,
+  publishScroll,
+  publishSwipe
+} from './publish'
 
 const _ = new WeakMap()
 
@@ -46,6 +51,6 @@ class Event {
   }
 }
 
-export { publishClick, publishEscape, publishSwipe }
+export { publishClick, publishEscape, publishScroll, publishSwipe }
 
 export default Event

src/publish.js

@@ -14,6 +14,28 @@ const publishEscape = ({ event, name = 'global.escape' }) => {
   })
 }
 
+const publishScroll = ({ event, limit = 10, name = 'global.scroll' }) => {
+  let lastPosition = 0
+  let lastTime = 0
+
+  window.addEventListener('scroll', () => {
+    const currentPosition = window.scrollY
+    const currentTime = Date.now()
+    const time = currentTime - lastTime
+
+    if (lastTime && time >= limit) {
+      const direction = currentPosition > lastPosition ? 'down' : 'up'
+      const distance = Math.abs(lastPosition - currentPosition)
+      const speed = distance / time
+
+      event.publish(name, { direction, speed })
+    }
+
+    lastTime = currentTime
+    lastPosition = currentPosition
+  })
+}
+
 const publishSwipe = ({
   event,
   name = 'global.swipe',
@@ -65,4 +87,4 @@ const publishSwipe = ({
   window.addEventListener('mouseup', e => swipeEnd(e))
 }
 
-export { publishClick, publishEscape, publishSwipe }
+export { publishClick, publishEscape, publishScroll, publishSwipe }