AxisX.svelte component

<!--
  @component
  Generates an SVG x-axis along the bottom of the chart. If the x scale is a band scale, each tick sits in the middle of its band.
 -->
<script>
  import { getLayerCakeContext } from 'layercake';

  const k = getLayerCakeContext();

  /**
   * @typedef {Object} Props
   * @property {boolean} [tickMarks=false] - Show a vertical mark at each tick.
   * @property {boolean} [gridlines=true] - Show gridlines extending into the chart area.
   * @property {number} [tickMarkLength=6] - The length of the tick mark.
   * @property {boolean} [showBaseline=false] - Show a solid line along the bottom of the chart.
   * @property {boolean} [snapLabels=false] - Instead of centering the text labels on the first and the last items, align them to the edges of the chart.
   * @property {(d: any) => string} [format=d => d] - Formats a tick value for display.
   * @property {number|Array<any>|((ticks: Array<any>) => Array<any>)} [ticks] - If this is a number, it passes that along to the [d3Scale.ticks](https://github.com/d3/d3-scale) function. If this is an array, hardcodes the ticks to those values. If it's a function, passes along the default tick values and expects an array of tick values in return. If nothing, it uses the default ticks supplied by the D3 function.
   * @property {number} [tickGutter=0] - The gap in pixels between the bottom of the chart area and the start of the tick.
   * @property {number} [dx=0] - Horizontal offset of the label in pixels.
   * @property {number} [dy=12] - Vertical offset of the label in pixels.
   */

  /** @type {Props} */
  let {
    tickMarks = false,
    gridlines = true,
    tickMarkLength = 6,
    showBaseline = false,
    snapLabels = false,
    format = d => d,
    ticks = undefined,
    tickGutter = 0,
    dx = 0,
    dy = 12
  } = $props();

  // Snapped labels anchor the first tick to the left edge and the last to the right
  /** @param {number} i */
  function textAnchor(i) {
    if (snapLabels === true) {
      if (i === 0) {
        return 'start';
      }
      if (i === tickVals.length - 1) {
        return 'end';
      }
    }
    return 'middle';
  }

  let tickLen = $derived(tickMarks === true ? (tickMarkLength ?? 6) : 0);

  let isBandwidth = $derived(typeof k.xScale.bandwidth === 'function');

  /** @type {Array<any>} */
  let tickVals = $derived(
    Array.isArray(ticks)
      ? ticks
      : isBandwidth
        ? k.xScale.domain()
        : typeof ticks === 'function'
          ? ticks(k.xScale.ticks())
          : k.xScale.ticks(ticks)
  );

  let halfBand = $derived(isBandwidth ? k.xScale.bandwidth() / 2 : 0);
</script>

<g class="axis x-axis" class:snapLabels>
  {#if showBaseline === true}
    <line class="baseline" y1={k.height} y2={k.height} x1="0" x2={k.width} />
  {/if}

  {#each tickVals as tick, i (tick)}
    <!-- Fall back to the chart height if the chart has no y dimension -->
    <g
      class="tick tick-{i}"
      transform="translate({k.xScale(tick)},{k.yRange ? Math.max(...k.yRange) : k.height})"
    >
      {#if gridlines === true}
        <line class="gridline" x1={halfBand} x2={halfBand} y1={-k.height} y2="0" />
      {/if}
      {#if tickMarks === true}
        <line
          class="tick-mark"
          x1={halfBand}
          x2={halfBand}
          y1={tickGutter}
          y2={tickGutter + tickLen}
        />
      {/if}
      <text x={halfBand} y={tickGutter + tickLen} {dx} {dy} text-anchor={textAnchor(i)}
        >{format(tick)}</text
      >
    </g>
  {/each}
</g>

<style>
  .tick {
    font-size: 11px;
  }

  line,
  .tick line {
    stroke: #aaa;
    stroke-dasharray: 2;
  }

  .tick text {
    fill: #666;
  }

  .tick .tick-mark,
  .baseline {
    stroke-dasharray: 0;
  }
  /* Push the snapped end labels 3px outward so they clear the chart edge */
  .axis.snapLabels .tick:last-child text {
    transform: translateX(3px);
  }
  .axis.snapLabels .tick.tick-0 text {
    transform: translateX(-3px);
  }
</style>