JSFiddle - React, Tailwind, and code Playground

by grant

HTML

<link rel="stylesheet" href="https://openlayers.org/en/v6.4.3/css/ol.css">
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.4.3/build/ol.js"></script>
<div id="map" class="map"></div>
    <label>
      Sea level
      <input id="level" type="range" min="100" max="200" value="1"/>
      +<span id="output"></span> m
    </label>
    <br>
    Go to
    <a class="location" data-center="-117.226,32.83" data-zoom="11">San Diego</a>,
    <a class="location" data-center="-122.3267,37.8377" data-zoom="11">San Francisco</a>,
    <a class="location" data-center="-73.9338,40.6861" data-zoom="11">New York</a>,
    <a class="location" data-center="72.9481,18.9929" data-zoom="11">Mumbai</a>, or
    <a class="location" data-center="120.831,31.160" data-zoom="9">Shanghai</a>

CSS

html, body {
        height: 100%;
        width: 100%;
        padding: 0px;
        margin: 0px;
      } 
      .map {
        height: 80%;
        width: 100%;
      }
      #level {
        display: inline-block;
        width: 150px;
        vertical-align: text-bottom;
      }

      a.location {
        cursor: pointer;
      }

JavaScript

/* Disable minification (remove `.min` from URL path) for more info */



function flood(pixels, data) {
        var pixel = pixels[0];
        if (pixel[3]) {
          var height = -10000 + ((pixel[0] * 256 * 256 + pixel[1] * 256 + pixel[2]) * 0.1);
          if (height <= data.level) {
            pixel[0] = 145;
            pixel[1] = 175;
            pixel[2] = 186;
            pixel[3] = 255;
          } else {
            pixel[3] = 0;
          }
        }
        return pixel;
      }

      var key = 'pk.eyJ1IjoiZ2VvY29kZXppcCIsImEiOiJjaWdtcnQyZzUwMDNnbmtrb2VvaXBsbnJuIn0.5UtgXcNHBy6JvtXudUQ3sA';
      var elevation = new ol.source.XYZ({
        url: 'https://api.mapbox.com/v4/mapbox.terrain-rgb/{z}/{x}/{y}.pngraw?access_token=' + key,
        crossOrigin: 'anonymous',
        transition: 0
      });

      var raster = new ol.source.Raster({ // RasterSource({
        sources: [elevation],
        operation: flood
      });

      var map = new ol.Map({
        target: 'map',
        layers: [
          new ol.layer.Tile({ // TileLayer({
            /* source: new ol.source.XYZ({
              url: 'https://api.mapbox.com/styles/v1/tschaub/ciutc102t00c62js5fqd47kqw/tiles/256/{z}/{x}/{y}?access_token=' + key
            }) */
            source: new ol.source.OSM()
          }),
          new ol.layer.Image({ // ImageLayer({
            opacity: 0.6,
            source: raster
          })
        ],
        view: new ol.View({
          center: ol.proj.fromLonLat([-122.3267, 37.8377]),
         //  center: ol.proj.fromLonLat([-116.09685, 43.76377]),
          zoom: 11
        })
      });

      var control = document.getElementById('level');
      var output = document.getElementById('output');
      control.addEventListener('input', function() {
        output.innerText = control.value;
        raster.changed();
      });
      output.innerText = control.value;

      raster.on('beforeoperations', function(event) {
        event.data.level =...