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Declarative D3 charts with React 16.3

The new React 16.3 brings some changes to the ecosystem that change how we go about integrating React and D3 to build data visualizations. I previously wrote about this in Declarative D3 transitions with React 16.3

componentWillReceiveProps, componentWillUpdate and componentWillMount are on their way out. They were great for making React and D3 happy together, but they cause issues with async rendering that the React team is planning for React 17.

You tend to use those now-deprecated lifecycle methods to update D3 objects’ internal state. Things like setting scale domains and ranges, updating complex D3 layouts, setting up transitions, etc.

But you don’t need to! You can do it all with the new lifecycle API.

Here’s a small example of building a bar chart with React 16.3. Using only approved lifecycle callbacks 😏

You can play with it on CodeSandbox 👇

How it works

The core problem we're solving is that D3 objects like to keep internal state and React doesn't like that. We have to update D3 objects whenever our React component gets new props.

You have to update a scale mapping data to x-axis pixels whenever either data or width change. Traditionally you would do that in componentWillReceiveProps.

React docs recommend replacing componentWillReceiveProps with componentDidUpdate, but that leads to rendering stale charts. If you update your D3 scales after your component re-renders, that's too late.

Instead, we can move our scales into state and use getDerivedStateFromProps. 🤯

d3 react 16.3

That's right, you can have complex objects in state now. It's totally safe.

Here's the gist of it 👇

D3 in state

Defining D3 objects as component properties used to be best. Now you should do it in your component state.

class BarChart extends React.Component {
state = {
widthScale: d3
.scaleBand()
.domain(d3.range(0, this.props.data.length))
.range([0, this.props.width]),
heightScale: d3
.scaleLinear()
.domain([0, d3.max(this.props.data)])
.range([0, this.props.height])
};

We define a widthScale and a heightScale. Each has a domain and a range that both depend on this.props. Yes you can do that in JavaScript class fields syntax.

Update D3 in getDerivedStateFromProps

You then use getDerivedStateFromProps to keep those scales up to date when your component updates.

static getDerivedStateFromProps(nextProps, prevState) {
let { widthScale, heightScale } = prevState;
widthScale.domain(d3.range(0, nextProps.data.length));
heightScale.domain([0, d3.max(nextProps.data)]);
prevState = { ...prevState, widthScale, heightScale };
return prevState;
}

It's a static method, which means no this keyword for you, you're running on the class, not an instance. You get the new props and the current state.

Take widthScale and heightScale out of props, update their domains, put them back. Probably should update their ranges too.

Render your chart

Now that your scales are always up to date, you can render your chart. Same as usual, D3 for props, React for rendering.

render() {
const { x, y, data, height } = this.props,
{ widthScale, heightScale } = this.state;
return (
<g transform="{`translate(${x}," ${y})`}="">
{data.map((d, i) => (
<rect x={widthScale(i)} y="{height" -="" heightscale(d)}="" width={widthScale.bandwidth()} height={heightScale(d)}>
))}
</rect></g>
);
}

Get chart coordinates, data, and height from props. Grab widthScale and heightScale. Return a <g> element full of rectangles.

Each rectangle is rendered in a loop and takes its coordinates and dimensions from our scales.

The result after a splash of color: A BarChart of random numbers where height and color correlate to the value. Simple chart in D3 and React 16.3 I also made a button that lets you add random values to the chart. That way you can see that it's updating perfectly declaratively. Update props and the chart updates. No need to understand implementation details.

You can play with it on CodeSandbox.

Pushing it too far

You can render 100,000 SVG nodes in CodeSandbox if you're patient. Then you can't edit your code anymore.

Did you enjoy this article?

Published on April 27th, 2018 in d3, Front End, react, react+d3js, Technical

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