feat: add a proof of concept

Using debouncing idea described in
https://css-tricks.com/styling-based-on-scroll-position/ to record
scrollY value and render the `BoxedTitle` base on the value. The box is
hidden when scrollY is greater than 30.

The class-style React component is used to register an event listener
for scrolling event.

src/components/HeaderBarebone/index.tsx

@@ -1,4 +1,4 @@
-import React from "react"
+import React, { Component } from "react"
 import cx from "classnames"
 
 import * as SC from "./styles"
@@ -16,6 +16,10 @@ interface IBoxedTitleProps {
   content?: React.ReactNode
 }
 
+type HeaderBareboneState = {
+  scrollY: Number
+}
+
 const BoxedTitle: React.FC<IBoxedTitleProps> = (props) => {
   return (
     <SC.Box>
@@ -35,22 +39,58 @@ const BoxedTitle: React.FC<IBoxedTitleProps> = (props) => {
   )
 }
 
-export const HeaderBarebone: React.FC<IHeaderBareboneProps> = (props) => {
-  const isBoxed = props.above || props.content
 
-  return (
-    <SC.HeaderWrapper className={props.className}>
-      <SC.Background />
-
-      <Container>
-        {isBoxed && (
-          <BoxedTitle above={props.above} content={props.content}>
-            {props.title}
-          </BoxedTitle>
-        )}
-
-        {!isBoxed && <SC.SingleTitle>{props.title}</SC.SingleTitle>}
-      </Container>
-    </SC.HeaderWrapper>
-  )
+const debounce = (fn) => {
+  let frame
+  return (...params) => {
+    if (frame) {
+      cancelAnimationFrame(frame)
+    }
+    frame = requestAnimationFrame(() => {
+      fn(...params)
+    })
+  }
+}
+
+export class HeaderBarebone extends Component<IHeaderBareboneProps, HeaderBareboneState> {
+
+  constructor(props) {
+    super(props)
+    this.tick = this.tick.bind(this)
+  }
+
+  tick() {
+    this.setState({
+      scrollY: window.scrollY
+    })
+  }
+
+  componentWillMount() {
+    this.tick()
+  }
+
+  componentDidMount() {
+    document.addEventListener('scroll', debounce(this.tick), { passive: true })
+  }
+
+  render() {
+    const props = this.props;
+    const isBoxed = props.above || props.content
+
+    return (
+        <SC.HeaderWrapper className={props.className}>
+        <SC.Background />
+
+        <Container>
+            {(isBoxed && this.state.scrollY < 30) && (
+            <BoxedTitle above={props.above} content={props.content}>
+                {props.title}
+            </BoxedTitle>
+            )}
+
+            {!isBoxed && <SC.SingleTitle>{props.title}</SC.SingleTitle>}
+        </Container>
+        </SC.HeaderWrapper>
+    )
+  }
 }