Draw d3-axis without direct DOM manipulation - dom

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>