MapLabels.html.svelte component

<!--
  @component
  Adds HTML text labels based features in the data or a custom GeoJSON Feature Collection.
 -->
<script>
  import { getContext } from 'svelte';

  const { data, width, height } = getContext('LayerCake');

  /** @type {Function} projection - A D3 projection function. Pass this in as an uncalled function, e.g. `projection={geoAlbersUsa}`. */
  export let projection;

  /** @type {Number|undefined} [fixedAspectRatio] - By default, the map fills to fit the $width and $height. If instead you want a fixed-aspect ratio, like for a server-side rendered map, set that here. */
  export let fixedAspectRatio = undefined;

  /** @type {Function} getLabel - An accessor function to get the field to display. */
  export let getLabel;

  /** @type {Function} [getCoordinates=d => d.geometry.coordinates] - An accessor function to get the `[x, y]` coordinate field. Defaults to a GeoJSON feature format. */
  export let getCoordinates;

  /** @type {Array<Object>|undefined} [features] - A list of labels as GeoJSON features. If unset, the plotted features will defaults to those in `$data.features`, assuming this field a list of GeoJSON features. */
  export let features = undefined;

  $: fitSizeRange = fixedAspectRatio ? [100, 100 / fixedAspectRatio] : [$width, $height];

  $: projectionFn = projection().fitSize(fitSizeRange, $data);

  $: units = fixedAspectRatio ? '%' : 'px';
</script>

<div class="map-labels" style:aspect-ratio={fixedAspectRatio ? 1 : null}>
  {#each features || $data.features as d}
    {@const coords = projectionFn(getCoordinates(d))}
    <div
      class="map-label"
      style="
      left: {coords[0]}{units};
      top: {coords[1]}{units};
    "
    >
      {getLabel(d)}
    </div>
  {/each}
</div>

<style>
  .map-labels {
    pointer-events: none;
    position: relative;
  }
  .map-label {
    position: absolute;
    text-align: center;
    font-size: 8px;
    color: #333;
    margin-top: -3px; /* To match the SVG labels, it needs a slight tweak */
    transform: translate(-50%, -50%);
  }
</style>