1 files changed, 67 insertions, 0 deletions
diff --git a/vnext/src/components/Header.js b/vnext/src/components/Header.js
new file mode 100644
index 00000000..fd1c1705
--- /dev/null
+++ b/vnext/src/components/Header.js
@@ -0,0 +1,67 @@
+import React from 'react';
+
+const elClassHidden = 'header--hidden'
+const elClassBackground = 'header--background';
+
+export default class Header extends React.Component {
+    constructor(props) {
+        super(props);
+        this.dHeight = 0;
+        this.wHeight = 0;
+        this.wScrollCurrent = 0;
+        this.wScrollBefore = 0;
+        this.wScrollDiff = 0;
+        this.header = React.createRef()
+    }
+    componentDidMount() {
+        const header = this.header.current;
+        window.addEventListener('scroll', this.throttle(250, () => {
+            this.dHeight = document.body.offsetHeight;
+            this.wHeight = window.innerHeight;
+            this.wScrollCurrent = window.pageYOffset;
+            this.wScrollDiff = this.wScrollBefore - this.wScrollCurrent;
+
+            if (this.wScrollCurrent <= 0) {
+                // scrolled to the very top; element sticks to the top
+                header.classList.remove(elClassHidden)
+                header.classList.remove(elClassBackground)
+            } else if (this.wScrollDiff > 0 && header.classList.contains(elClassHidden)) {
+                // scrolled up; element slides in
+                header.classList.remove(elClassHidden)
+                header.classList.add(elClassBackground)
+            } else if (this.wScrollDiff < 0) {
+                // scrolled down
+                if (this.wScrollCurrent + this.wHeight >= this.dHeight && header.classList.contains(elClassHidden)) {
+                    // scrolled to the very bottom; element slides in
+                    header.classList.remove(elClassHidden)
+                    header.classList.add(elClassBackground)
+                } else {
+                    // scrolled down; element slides out
+                    header.classList.add(elClassHidden)
+                }
+            }
+            this.wScrollBefore = this.wScrollCurrent;
+        }), { passive: true });
+    }
+    throttle(delay, fn) {
+        var last, deferTimer;
+        return function () {
+            var context = this, args = arguments, now = +new Date;
+            if (last && now < last + delay) {
+                clearTimeout(deferTimer);
+                deferTimer = setTimeout(
+                    function () {
+                        last = now;
+                        fn.apply(context, args);
+                    },
+                    delay);
+            } else {
+                last = now;
+                fn.apply(context, args);
+            }
+        };
+    };
+    render() {
+        return (<header ref={this.header}>{this.props.children}</header>);
+    }
+}
+\ No newline at end of file