AxisY.svelte component

<!--
  @component
  Generates an SVG y-axis along the left edge of the chart. If the y 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 horizontal mark at each tick.
   * @property {'even'|'above'} [labelPosition='even'] - Whether the label sits level with its tick ('even') or above it ('above').
   * @property {boolean} [snapBaselineLabel=false] - When labelPosition='even', adjust the lowest label so that it sits above the tick mark.
   * @property {boolean} [gridlines=true] - Show gridlines extending into the chart area.
   * @property {number} [tickMarkLength] - Length of the tick mark in pixels. Defaults to the width of the widest label when `labelPosition` is 'above', otherwise 6.
   * @property {(d: any) => string} [format=d => d] - Formats a tick value for display.
   * @property {number|Array<any>|((ticks: Array<any>) => Array<any>)} [ticks=4] - 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.
   * @property {number} [tickGutter=0] - The gap in pixels between the left edge of the chart area and the tick.
   * @property {number} [dx=0] - Horizontal offset of the label in pixels.
   * @property {number} [dy=0] - Vertical offset of the label in pixels.
   * @property {number} [charPixelWidth=7.25] - Used to calculate the widest label length to offset labels. Adjust if the automatic tick length doesn't look right because you have a bigger font (or just set `tickMarkLength` to a pixel value).
   */

  /** @type {Props} */
  let {
    tickMarks = false,
    labelPosition = 'even',
    snapBaselineLabel = false,
    gridlines = true,
    tickMarkLength = undefined,
    format = d => d,
    ticks = 4,
    tickGutter = 0,
    dx = 0,
    dy = 0,
    charPixelWidth = 7.25
  } = $props();

  /** @param {number} sum
   *  @param {string} val */
  function calcStringLength(sum, val) {
    if (val === ',' || val === '.') return sum + charPixelWidth * 0.5;
    return sum + charPixelWidth;
  }

  let isBandwidth = $derived(typeof k.yScale.bandwidth === 'function');
  /** @type {Array<any>} */
  let tickVals = $derived(
    Array.isArray(ticks)
      ? ticks
      : isBandwidth
        ? k.yScale.domain()
        : typeof ticks === 'function'
          ? ticks(k.yScale.ticks())
          : k.yScale.ticks(ticks)
  );
  let widestTickLen = $derived(
    Math.max(
      10,
      Math.max(...tickVals.map(d => format(d).toString().split('').reduce(calcStringLength, 0)))
    )
  );
  let tickLen = $derived(
    tickMarks === true
      ? labelPosition === 'above'
        ? (tickMarkLength ?? widestTickLen)
        : (tickMarkLength ?? 6)
      : 0
  );
  let x1 = $derived(-tickGutter - (labelPosition === 'above' ? widestTickLen : tickLen));
  let halfBand = $derived(isBandwidth ? k.yScale.bandwidth() / 2 : 0);
  let maxTickValPx = $derived(Math.max(...tickVals.map(k.yScale)));
</script>

<g class="axis y-axis">
  {#each tickVals as tick (tick)}
    {@const tickValPx = k.yScale(tick)}
    <!-- Fall back to the left edge if the chart has no x dimension -->
    <g class="tick tick-{tick}" transform="translate({k.xRange ? k.xRange[0] : 0}, {tickValPx})">
      {#if gridlines === true}
        <line class="gridline" {x1} x2={k.width} y1={halfBand} y2={halfBand}></line>
      {/if}
      {#if tickMarks === true}
        <line class="tick-mark" {x1} x2={x1 + tickLen} y1={halfBand} y2={halfBand}></line>
      {/if}
      <text
        x={x1}
        y={halfBand}
        dx={dx + (labelPosition === 'even' ? -3 : 0)}
        text-anchor={labelPosition === 'above' ? 'start' : 'end'}
        dy={dy +
          (labelPosition === 'above' || (snapBaselineLabel === true && tickValPx === maxTickValPx)
            ? -3
            : 4)}>{format(tick)}</text
      >
    </g>
  {/each}
</g>

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

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

  .tick text {
    fill: #666;
  }

  /* A solid line at the zero tick */
  .tick.tick-0 line {
    stroke-dasharray: 0;
  }
</style>