Intro to SVG for React Developers


This lesson assumes familiarity with HTML, CSS, and the basic principles of React but very little knowledge of SVG.

The artful combination of HTML and CSS is a tried-and-true solution for creating simple graphics like notification badges and arrows. Anything more complex can result in a mess of nested div elements and mile-long CSS rules.

SVG is here to help.

From simple glyphs to complex visualizations, you can use SVG to create reusable React components that render precise vector graphics, all without any additional libraries or tools.

In this lesson, we'll build a colorful spinning loading indicator, a <Spinner /> React component, using some very simple SVG markup.

You may be familiar with SVG (Scalable Vector Graphics) as a file format for vector images on the web, where they can be displayed with the same img tags that you use for jpg, gif, and png files:

<img src="image.svg">

If you've ever opened an SVG file with a text editor, you'll know that it looks a lot like HTML. In fact, SVG code can be mixed right in with HTML. The following is a valid page, and renders a 100 pixel wide image of a blue circle with a gray border:

<!DOCTYPE html>
<html> <head> <title>SVG</title> </head> <body> <svg viewBox="0 0 100 100" width="100"> <circle fill="lightblue" stroke="darkgray" cx="50" cy="50" r="45"/> </svg> </body>
</html>

This circle is a good starting place for our spinner.

Create the spinner component

Let's take the SVG in the code above and turn it into a basic React component. Along the way, let's make our circle's outline a little thicker by adding the strokeWidth attribute:

import React from 'react'; function Spinner() { return ( <svg viewBox="0 0 100 100" width="100"> <circle fill="lightblue" stroke="darkgray" strokeWidth="4" cx="50" cy="50" r="45"/> </svg> );
} export default Spinner;

As you've probably inferred, the circle tag's attributes cx and cy are the coordinates of the circle's center, and r is the circle's radius.

Side Note: What might not be as obvious is the svg element's viewBox attribute. You use viewBox to establish the coordinate space of the SVG. In this case, the top left corner is specified by the first two numbers, 0 0, and the bottom right by the second two, 100 100. This means the svg is 100 units wide and tall, and the center of the svg is at 50 50. Try tweaking the viewBox values and see how the image changes.

Add more shapes

Spinners need something to spin, right? So let's make some more shapes!

Below the <circle> element, add a translucent white square. The attributes of a rect are fairly straightforward, but you might have noticed the unusual strokeOpacity attribute. In addition to setting overall opacity as with HTML, SVG allows you to set independent opacity values for a shape's fill and stroke. Feel the power!

<rect x="25" y="25" width="50" height="50" stroke="darkgray" fill="white" fillOpacity=".5" strokeWidth="4"/>

Next, let's add a green hexagon. This is where the power of drawing with SVG starts to outshine what can be accomplished with pure HTML and CSS.

The points attribute is simply a list of points that correspond to the corners of your polygon:

<polygon points="63,57.5 50,65 37,57 37,42.5 50,35 63,42.5" fill="lightgreen" strokeWidth="4" stroke="darkgray" />

Easy! Try changing, removing, or adding new numbers in the points attribute around to see what happens.

Your component now has some shapes to spin, but before we get them spinning, let's discuss how we can use CSS in conjunction with SVG to make our lives easier.

Stylesheets

Like HTML, SVG can be styled with CSS. Attributes like fill, stroke, and path can be specified in your styles, and CSS transitions and animations also work with SVG.

Let's add className attributes to our shapes:

<circle className="spinner circle" fill="lightblue" strokeWidth="4" stroke="darkgray" cx="50" cy="50" r="45"/>
<rect className="spinner rect" x="25" y="25" width="50" height="50" stroke="darkgray" fill="white" fillOpacity=".5" strokeWidth="4"/>
<polygon className="spinner hex" points="63,57.5 50,65 37,57 37,42.5 50,35 63,42.5" fill="lightgreen" strokeWidth="4" stroke="darkgray" />

Move the styling attributes out of your shape elements and into your stylesheet:

.spinner { stroke: darkgray; stroke-width: 4;
} .circle { fill: lightblue;
} .rect { fill: white; fill-opacity: .5;
} .hex { fill: lightgreen;
}

Your SVG code should now look like this:

<circle className="spinner circle" cx="50" cy="50" r="45"/>
<rect className="spinner rect" x="25" y="25" width="50" height="50" />
<polygon className="spinner hex" points="63,57.5 50,65 37,57 37,42.5 50,35 63,42.5" />

Ah, much more concise. Now, let's finally get that spinner spinning!

Animation

In your stylesheet, create a simple CSS animation for rotation:

@keyframes rotation { from { transform: rotate(0deg); } to { transform: rotate(359deg); }
}

Apply the animation to the hexagon:

.hex { fill: lightgreen; animation: rotation 2s infinite;
}

To make things interesting, let's apply the same animation to the rectangle, but mix up the direction and timing:

.rect { fill: white; fill-opacity: .5; animation: rotation 2s infinite alternate-reverse;
}

Congratulations, you're now the owner an animated SVG component with two spinning shapes! Put it anywhere in your React app with the simple tag:

<Spinner />

Challenges

Some tasks you can challenge yourself with:

  • Break the hexagon shape out into its own React component and use them within the <Spinner /> component.

  • Pass an attribute to the spinner that controls how fast the spinner spins, like this: <Spinner speed="fast|slow" /> (hint: using class names is one approach)

  • Research how to use text with SVG and pass a loading message into the spinner component like this: <Spinner message="loading..." />

Next steps

We've only scratched the surface of what you can accomplish by pairing SVG with React. I encourage you to dive deeper into SVG and read up on additional tags such as ellipse, line, and path. Experiment with features like gradient fills and clipping masks.

Once you're more comfortable with SVG, your mind will hopefully start bubbling with ideas about how the composability of React components can be leveraged to create composable graphics.

Happy drawing!