AxisY.svelte component

<!--
  @component
  Generates an SVG y-axis. This component is also configured to detect if your y-scale is an ordinal scale. If so, it will place the tickMarks in the middle of the bandwidth.
 -->
<script>
  import { getContext } from 'svelte';

  const { xRange, yScale, width } = getContext('LayerCake');

  /** @type {Boolean} [tickMarks=false] - Show marks next to the tick label. */
  export let tickMarks = false;

  /** @type {String} [labelPosition='even'] - Whether the label sits even with its value ('even') or sits on top ('above') the tick mark. Default is 'even'. */
  export let labelPosition = 'even';

  /** @type {Boolean} [snapBaselineLabel=false] - When labelPosition='even', adjust the lowest label so that it sits above the tick mark. */
  export let snapBaselineLabel = false;

  /** @type {Boolean} [gridlines=true] - Show gridlines extending into the chart area. */
  export let gridlines = true;

  /** @type {Number} [tickMarkLength=undefined] - The length of the tick mark. If not set, becomes the length of the widest tick. */
  export let tickMarkLength = undefined;

  /** @type {Function} [format=d => d] - A function that passes the current tick value and expects a nicely formatted value in return. */
  export let format = d => d ;

  /** @type {Number|Array|Function} [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. */
  export let ticks = 4;

  /** @type {Number} [tickGutter=0] - The amount of whitespace between the start of the tick and the chart drawing area (the xRange min). */
  export let tickGutter = 0;

  /** @type {Number} [dx=0] - Any optional value passed to the `dx` attribute on the text label. */
  export let dx = 0;

  /** @type {Number} [dy=0] - Any optional value passed to the `dy` attribute on the text label. */
  export let dy = 0;

  /** @type {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). */
  export let charPixelWidth = 7.25;

  $: isBandwidth = typeof $yScale.bandwidth === 'function';

  $: tickVals = Array.isArray(ticks) ? ticks :
    isBandwidth ?
      $yScale.domain() :
      typeof ticks === 'function' ?
        ticks($yScale.ticks()) :
          $yScale.ticks(ticks);

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

  $: tickLen = tickMarks === true
    ? labelPosition === 'above'
      ? tickMarkLength ?? widestTickLen
      : tickMarkLength ?? 6
    : 0;

  $: widestTickLen = Math.max(10, Math.max(...tickVals.map(d => format(d).toString().split('').reduce(calcStringLength, 0))));

  $: x1 = -tickGutter - (labelPosition === 'above' ? widestTickLen : tickLen);
  $: y = isBandwidth ? $yScale.bandwidth() / 2 : 0;

  $: maxTickValPx = Math.max(...tickVals.map($yScale));
</script>

<g class='axis y-axis'>
  {#each tickVals as tick (tick)}
    {@const tickValPx = $yScale(tick)}
    <g class='tick tick-{tick}' transform='translate({$xRange[0]}, {tickValPx})'>
      {#if gridlines === true}
        <line
          class="gridline"
          {x1}
          x2='{$width}'
          y1={y}
          y2={y}
        ></line>
      {/if}
      {#if tickMarks === true}
        <line
          class='tick-mark'
          {x1}
          x2={x1 + tickLen}
          y1={y}
          y2={y}
        ></line>
      {/if}
      <text
        x='{x1}'
        {y}
        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;
  }

  .tick.tick-0 line {
    stroke-dasharray: 0;
  }
</style>