Draw d3-axis without direct DOM manipulation

Question

Is there a way to use d3-axis without directly manipulating the DOM? D3.js complements Vue.js nicely when used for its helper functions (especially d3-scale).

I'm currently using a simple Vue template to generate a SVG. To generate the axis, I am first creating a <g ref="axisX"> element and then calling d3.select(this.$refs.axisX).call(d3.axisBottom(this.scale.x)).

I would like to avoid using d3.select to prevent direct DOM modifications. It works well but it conflicts with Vue.js' scoped styles.

Is there a way to access d3-axis without calling it from a DOM element? It would be useful to have access to its path generation function independently instead of via the DOM.

Here is a sample CodePen: https://codepen.io/thibautg/pen/BYRBXW

Answer 1

This is a situation that calls for a custom directive. Custom directives allow you to manipulate the DOM within the element they are attached to.

In this case, I created a directive that takes an argument for which axis and a value which is your scale computed. Based on whether the axis is x or y, it calls axisBottom or axisLeft with scale[axis].

No more watching. The directive will be called any time anything updates. You could put in a check to see whether scale in particular had changed from its previous value, if you wanted.

new Vue({
  el: "#app",
  data() {
    return {
      width: 600,
      height: 400,
      margin: {
        top: 20,
        right: 20,
        bottom: 20,
        left: 20
      },
      items: [
        { name: "a", val: 10 },
        { name: "b", val: 8 },
        { name: "c", val: 1 },
        { name: "d", val: 5 },
        { name: "e", val: 6 },
        { name: "f", val: 3 }
      ]
    };
  },
  computed: {
    outsideWidth() {
      return this.width + this.margin.left + this.margin.right;
    },
    outsideHeight() {
      return this.height + this.margin.top + this.margin.bottom;
    },
    scale() {
      const x = d3
        .scaleBand()
        .domain(this.items.map(x => x.name))
        .rangeRound([0, this.width])
        .padding(0.15);
      const y = d3
        .scaleLinear()
        .domain([0, Math.max(...this.items.map(x => x.val))])
        .rangeRound([this.height, 0]);
      return { x, y };
    }
  },
  directives: {
    axis(el, binding) {
      const axis = binding.arg;
      const axisMethod = { x: "axisBottom", y: "axisLeft" }[axis];
      const methodArg = binding.value[axis];

      d3.select(el).call(d3[axisMethod](methodArg));
    }
  }
});

rect.bar {
  fill: steelblue;
}

<script src="//unpkg.com/vue@2"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/d3/4.11.0/d3.min.js"></script>
<div id="app">
  <svg :width="outsideWidth"
       :height="outsideHeight">
    <g :transform="`translate(${margin.left},${margin.top})`">
      <g class="bars">
        <template v-for="item in items">
          <rect class="bar"
                :x="scale.x(item.name)"
                :y="scale.y(item.val)"
                :width="scale.x.bandwidth()"
                :height="height - scale.y(item.val)"
                />
        </template>
        <g v-axis:x="scale" :transform="`translate(0,${height})`"></g>
        <g v-axis:y="scale"></g>
      </g>
    </g>
  </svg>
</div>