Cannot get D3.js to work inside Svelte component (with Rollup)

user_7959373 0
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I've been trying to put the most basic D3 example into a Svelte app and can't get it to work. At first I tried installing D3 as a node module: npm install d3 but this produces the same result (a lack of result) as importing D3 as an external script from CDN inside of index.html: <script src="https://d3js.org/d3.v5.min.js"></script>. Using either method I get a bunch of circular dependency warnings on app start:

(!) Circular dependency: node_modules\d3-selection\src\selection\index.js -> node_modules\d3-selection\src\selection\select.js -> node_modules\d3-selection\src\selection\index.js

But the app starts with no errors, and no D3 dynamic formatting occurs, nor any errors pop up in the DevTools console inside Chrome.

The Svelte component looks like this:

<script>
    import * as d3 from 'd3';
    var data = [30, 86, 168, 281, 303, 365];

    d3.select(".chart")
        .selectAll("div")
        .data(data)
        .enter()
        .append("div")
        .style("width", function(d) {
        return d + "px";
        })
        .text(function(d) {
        return d;
        });
</script>

<style>
      .chart div {
    font: 10px sans-serif;
    background-color: steelblue;
    text-align: right;
    padding: 3px;
    margin: 1px;
    color: white;
  }
</style>

<div class="chart"></div>

Putting the code above into a static HTML file produces a bar chart, as expected. But when run as a Svelte component nothing is displayed.

My rollup.config.js is:

import svelte from 'rollup-plugin-svelte';
import resolve from 'rollup-plugin-node-resolve';
import commonjs from 'rollup-plugin-commonjs';
import livereload from 'rollup-plugin-livereload';
import { terser } from 'rollup-plugin-terser';

const production = !process.env.ROLLUP_WATCH;

export default {
    input: 'src/main.js',
    output: {
        sourcemap: true,
        format: 'iife',
        name: 'app',
        file: 'public/bundle.js',
        globals: { 'd3': 'd3' },
        external: [ 'd3' ]
    },
    plugins: [
        svelte({
            dev: !production,
            css: css => { css.write('public/bundle.css'); }
        }),
        resolve({ browser: true }),
        commonjs(),
        !production && livereload('public'),
        production && terser()
    ],
    watch: {
        clearScreen: false
    }
};

...and index.html is:

<!doctype html>
<html>
<head>
    <meta charset='utf8'>
    <meta name='viewport' content='width=device-width'>

    <title>Svelte app</title>

    <link rel='icon' type='image/png' href='favicon.png'>
    <link rel='stylesheet' href='global.css'>
    <link rel='stylesheet' href='bundle.css'>
</head>

<body>
    <script src="https://d3js.org/d3.v5.min.js"></script>
    <script src='bundle.js'></script>
</body>
</html>

I would suspect Rollup not bundling D3 module correctly, but as an external script in <body> it should in theory work, but it doesn't. Please point me in the right direction, I've spent way too much time trying to get it to work, and as a JS noob am out of options. Thanks!

rollupjs d3.js svelte javascript
1 Answers

The <div class="chart"></div> element doesn't exist when your code first runs — the contents of <script> run when the component is instantiated. If you need to access DOM elements inside the component, it will first be available inside onMount:

<script>
  import { onMount } from 'svelte';

  // other code...

  onMount(() => {
    d3.select('.chart')
      // ...
  });
</script>

Using a selector like .chart is dangerous though, because if you had more than one component on the page D3 would select the wrong thing. It's better to use bind:this instead:

<script>
  import { onMount } from 'svelte';

  // other code...

  let el;

  onMount(() => {
    d3.select(el) // no danger of selecting the wrong element
      // ...
  });
</script>

<div class="chart" bind:this={el}></div>

Now all you need to change is the CSS — because Svelte will discard selectors that it thinks are unused, and because it can't know what D3 is going to do, it will remove .chart div {...}. Instead, use the :global(...) modifier to target divs inside your top-level element:

<style>
  .chart :global(div) {
    /* styles */
  }
</style>

With those changes, it works perfectly:

https://svelte.dev/repl/8722c32f4e1a44a98e3a3fc8a095b2d7?version=3.5.3

But in this case, D3 isn't really bringing anything to the party. You could achieve the same result much more simply:

<script>
  var data = [30, 86, 168, 281, 303, 365];
</script>

<style>
  .chart div {
    font: 10px sans-serif;
    background-color: steelblue;
    text-align: right;
    padding: 3px;
    margin: 1px;
    color: white;
  }
</style>

<div class="chart">
  {#each data as d}
    <div style="width: {d}px">
      {d}
    </div>
  {/each}
</div>

As well as being less code for you to write, your app now contains a lot less JavaScript. Demo here: https://svelte.dev/repl/be5cac1695554b8e9ee6d0bc14b9dff1?version=3.5.3

user_27423960
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