Sticky categories label

css/emoji-picker.css

@@ -8,7 +8,7 @@
   font-size: 16px;
   display: inline-block;
   color: #222427;
-  border: 1px solid rgba(0, 0, 0, .15);
+  border: 1px solid #d9d9d9;
   border-radius: 5px;
 }
 
@@ -28,8 +28,8 @@
 .emoji-picker-scroll {
   overflow: scroll;
   max-height: 270px;
-  padding: 6px;
-  border: solid rgba(0, 0, 0, .15);
+  padding: 0 6px 6px 6px;
+  border: solid #d9d9d9;
   border-width: 1px 0;
 }
 
@@ -38,8 +38,9 @@
   display: block;
   width: 100%;
   padding: .2em .6em;
+  margin-top: 6px;
   border-radius: 25px;
-  border: 1px solid rgba(0, 0, 0, .15);
+  border: 1px solid #d9d9d9;
   outline: 0;
 }
 
@@ -48,8 +49,17 @@
 }
 
 .emoji-picker-category-label {
+  position: relative;
+  position: -webkit-sticky;
+  top: 0;
+}
+
+.emoji-picker-category-label span {
+  display: block;
+  width: 100%;
   font-weight: bold;
   padding: 5px 6px;
+  background-color: #fff;
   background-color: rgba(255, 255, 255, .95);
 }
 

src/components/category.js

@@ -2,32 +2,67 @@ import React from 'react'
 import Emoji from './emoji'
 
 export default class Category extends React.Component {
-  shouldComponentUpdate(props) {
-    if (props.perLine != this.props.perLine) {
-      return true
+  componentDidMount() {
+    this.container = this.refs.container
+    this.label = this.refs.label
+    this.parent = this.container.parentNode
+
+    this.margin = 0
+    this.minMargin = 0
+
+    this.memoizeSize()
   }
 
-    for (let k in props.emojiProps) {
-      if (props.emojiProps[k] != this.props.emojiProps[k]) {
-        return true
-      }
+  componentDidUpdate() {
+    this.memoizeSize()
   }
 
-    return false
+  memoizeSize() {
+    var { top, height } = this.container.getBoundingClientRect()
+    var { top: parentTop } = this.parent.getBoundingClientRect()
+    var { height: labelHeight } = this.label.getBoundingClientRect()
+
+    this.top = top - parentTop + this.parent.scrollTop
+    this.maxMargin = height - labelHeight
+  }
+
+  handleScroll(scrollTop) {
+    var margin = scrollTop - this.top
+    margin = margin < this.minMargin ? this.minMargin : margin
+    margin = margin > this.maxMargin ? this.maxMargin : margin
+
+    if (margin == this.margin) return
+    this.label.style.top = `${margin}px`
+    this.margin = margin
   }
 
   render() {
-    var { name, emojis, perLine, emojiProps } = this.props,
+    var { name, emojis, perLine, hasStickyPosition, emojiProps } = this.props,
         emojis = emojis.slice(0),
         lines = [],
-        linesCount = Math.ceil(emojis.length / perLine)
+        linesCount = Math.ceil(emojis.length / perLine),
+        labelStyles = {},
+        labelSpanStyles = {}
 
     Array(linesCount).fill().forEach((_, i) =>
       lines.push(emojis.splice(0, perLine))
     )
 
-    return <div className='emoji-picker-category'>
-      <div className='emoji-picker-category-label'>{name}</div>
+    if (!hasStickyPosition) {
+      labelStyles = {
+        height: 28,
+      }
+
+      labelSpanStyles = {
+        position: 'absolute',
+      }
+    }
+
+    return <div ref='container' className='emoji-picker-category'>
+      <div style={labelStyles} data-name={name} className='emoji-picker-category-label'>
+        <span style={labelSpanStyles} ref='label'>{name}</span>
+      </div>
+
       {lines.map((emojis, i) =>
         <div key={`line-${i}`}>
           {emojis.map((emoji) =>
@@ -45,6 +80,7 @@ export default class Category extends React.Component {
 
 Category.propTypes = {
   emojis: React.PropTypes.array,
+  hasStickyPosition: React.PropTypes.bool,
   name: React.PropTypes.string.isRequired,
   perLine: React.PropTypes.number.isRequired,
   emojiProps: React.PropTypes.object.isRequired,
@@ -52,4 +88,5 @@ Category.propTypes = {
 
 Category.defaultProps = {
   emojis: [],
+  hasStickyPosition: true,
 }

src/components/picker.js

@@ -5,11 +5,38 @@ import Preview from './preview'
 import Category from './category'
 
 export default class Picker extends React.Component {
+  componentWillMount() {
+    var stickyTestElement = document.createElement('div')
+    for (let prefix of ['', '-webkit-', '-ms-', '-moz-', '-o-']) {
+      stickyTestElement.style.position = `${prefix}sticky`
+    }
+
+    this.hasStickyPosition = !!stickyTestElement.style.position.length
+  }
+
+  componentDidUpdate() {
+    this.handleScroll()
+  }
+
   handleEmojiOver(emoji) {
     var { preview } = this.refs
     preview.setState({ emoji: emoji })
   }
 
+  handleScroll() {
+    var target = this.refs.scroll,
+        scrollTop = target.scrollTop
+
+    if (!this.hasStickyPosition) {
+      Array(data.categories.length).fill().forEach((_, i) => {
+        var category = this.refs[`category-${i}`]
+        if (category) {
+          category.handleScroll(scrollTop)
+        }
+      })
+    }
+  }
+
   render() {
     var { perLine, emojiSize, sheetURL } = this.props
 
@@ -18,20 +45,22 @@ export default class Picker extends React.Component {
         Categories
       </div>
 
-      <div ref="scroll" className='emoji-picker-scroll'>
+      <div ref="scroll" className='emoji-picker-scroll' onScroll={this.handleScroll.bind(this)}>
         <input
           type='text'
           placeholder='Search'
           className='emoji-picker-search'
         />
 
-        {data.categories.map((category) => {
+        {data.categories.map((category, i) => {
           if (category.name == 'Skins') return null
           return <Category
+            ref={`category-${i}`}
             key={category.name}
             name={category.name}
             emojis={category.emojis}
             perLine={perLine}
+            hasStickyPosition={this.hasStickyPosition}
             emojiProps={{
               size: emojiSize,
               sheetURL: sheetURL,