Departures board

Simulating a split-flap display with CSS animations, advancing the letters on each animationiteration event.

<!DOCTYPE html>
<meta charset="utf-8">
<link href="https://fonts.googleapis.com/css?family=Roboto+Condensed" rel="stylesheet">
<style>
  body {
    background-color: #222;
    font: 116px "Roboto Condensed";
    color: #ecdb41;
    text-align: center;
  }
  div {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
  }
  span {
    position: relative;
  }
  .container {
    top: 44px;
    left: 12px;
  }
  .flap {
    width: 110px;
    right: auto;
  }
  .half {
    height: 62px;
    overflow: hidden;
    background: #444;
    transform-style: preserve-3d;
    animation-timing-function: ease-in;
    animation-duration: 0.28s;
    animation-iteration-count: infinite;
  }
  .fast .half {
    animation-duration: 0.14s;
  }
  .divider {
    top: 61px;
    height: 2px;
    background: #222;
  }
  .prev {
    top: 62px;
  }
  .back,
  .front {
    backface-visibility: hidden;
  }
  .front {
    transform-origin: center bottom;
  }
  .back {
    top: 62px;
    transform-origin: center top;
  }
  .front span,
  .next span {
    top: -6px;
  }
  .back span,
  .prev span {
    top: -68px;
  }
  .animated .front {
    animation-name: flipFront;
  }
  .animated .back {
    animation-name: flipBack;
  }
  @keyframes flipFront {
    0% {
      transform: rotateX(0deg);
      background-color: #444;
    }
    100% {
      transform: rotateX(180deg);
      background-color: #1c1c1c;
    }
  }
  @keyframes flipBack {
    0% {
      transform: rotateX(180deg);
      background-color: #222;
    }
    100% {
      transform: rotateX(0deg);
      background-color: #444;
    }
  }
</style>
<div class="container"></div>
<script src="//d3js.org/d3.v4.min.js"></script>
<script>

let cities = [
  "NEW YORK",
  "MIAMI",
  "CHICAGO",
  "BOSTON",
  "ATLANTA",
  "SEATTLE",
  "PARIS",
  "MOSCOW",
  "SHANGHAI",
  "BANGKOK",
  "TORONTO",
  "BEIJING",
  "ATHENS",
  "BERLIN",
  "LONDON",
  "TOKYO",
  "SEOUL",
  "MUMBAI",
  "CAIRO",
  "ISTANBUL",
  "SYDNEY",
  "BRUSSELS"
].map(d => d.padEnd(8));

d3.shuffle(cities);

let cycle = {};

for (let i = 65; i < 90; i++) {
  cycle[String.fromCharCode(i)] = String.fromCharCode(i + 1);
}

cycle["Z"] = " ";
cycle[" "] = "A";

let rows = d3.select(".container")
  .selectAll(".row")
  .data(cities.splice(0, 3))
  .enter()
  .append("div")
    .attr("class", "row")
    .style("top", (d, i) => i * 144 + "px");

let flaps = rows.selectAll("div")
  .data(city => city.split(""))
  .enter()
  .append("div")
    .attr("class", "flap")
    .style("left", (d, i) => i * 118 + "px");

["next", "prev", "back", "front"].forEach(d => {
  if (d === "front") {
    flaps.append("div")
      .attr("class", "divider");
  }

flaps.append("div")
    .attr("class", "half " + d)
    .append("span")
      .text(letter => letter);
});

cities.push(...rows.data());
flip();

function flipLetter(flap, fromLetter, toLetter, cb) {
  let current = fromLetter,
    next = cycle[fromLetter],
    prevFlaps = flap.selectAll(".prev span, .front span"),
    nextFlaps = flap.selectAll(".back span, .next span"),
    fast;

flap.select(".front").on("animationiteration", function() {
    if (next === toLetter) {
      flap.classed("animated fast", false)
        .selectAll("span")
          .text(toLetter);
      return cb();
    }

if (!fast) {
      fast = flap.classed("fast", true);
    }

prevFlaps.text(next);

current = next;
    next = cycle[next];

setTimeout(function() {
      nextFlaps.text(next);
    }, 0);
  });

flap.classed("animated", true);

nextFlaps.text(next);
}
</script>

https://d3js.org/d3.v4.min.js