Here's a fun problem for ya: How do you get the CSS from a rendered React component?
Right-click, inspect element, see it in dev tools. D'oh 🙄
What about programmatically?
Turns out that's not so easy.
You could, for example, try the
window.getComputedStyle method. Same as that DevTools view with all the styles.
But that's too much stuff. You get values for every CSS property that exists in the spec. 😅
What else can you try?
Well there's always the
style prop. You could get its value and hope for the best.
But that only works if you're actually using it. Most people these days do not. Sure it's plenty useful for one-off overrides, but when was the last time you saw a project that heavily relies on the style prop?
Exactly. Not in a while.
Most projects have settled on styled-components or CSS modules. That makes our job both easier and harder. 🤨
You can watch me figure this one out in a livestream 👇
I tried all of the above and then some. Here's the solution I came up with: 👨🎨 component-css-extractor. Open sourced for your ease of use 😊
CodeSandbox to prove it works 👇
👨🎨 component-css-extractor relies on the fact that both styled-components and CSS modules use class names.
Each styled component that you write is assigned a unique class name. Rendered components get the class property, CSS rules go in a
<style> tag in your header.
We can combine those to get a clean set of CSS rules. Scoped to the target component with nothing extra to mess us up. 👌
34 lines of prettified code in total 👇
As the comments say:
- Collect class names for entire subtree
document.head.getElementsByTagName("style")to get all
- Use the
- Filter rules that don't apply to our classes
- Stringify and return
Works like a charm 👨🎨
As always there are some limitations.
First of all, this won't work on the server or during build time. Collecting
<style> tags requires access to the DOM as it exists in the browser. You don't have that during server-side-rendering, I think.
Fortunately you don't need 👨🎨 component-css-extractor on the server. Styled-components has a built-in way of extracting styles into a string for serving to the client.
The built-in way doesn't work in the browser, hence why I went down this rabbit hole.
Second of all, if you have global stylesheets in a
.css file, 👨🎨 component-css-extractor won't pick those up. Makes the code simpler.
Imagine having to parse all of CSS in all your stylesheets and figuring out what does and doesn't apply to a particular DOM node. Might as well build a browser rendering engine lol.
Happy Monday, ~Swizec
I write articles with real insight into the career and skills of a modern software engineer. "Raw and honest from the heart!" as one reader described them. Fueled by lessons learned over 20 years of building production code for side-projects, small businesses, and hyper growth startups. Both successful and not.
Subscribe below 👇
Join Swizec's Newsletter and get insightful emails 💌 on mindsets, tactics, and technical skills for your career. Real lessons from building production software. No bullshit.
"Man, love your simple writing! Yours is the only newsletter I open and only blog that I give a fuck to read & scroll till the end. And wow always take away lessons with me. Inspiring! And very relatable. 👌"
Senior Mindset Book
Get promoted, earn a bigger salary, work for top companiesLearn more
Have a burning question that you think I can answer? Hit me up on twitter and I'll do my best.
Who am I and who do I help? I'm Swizec Teller and I turn coders into engineers with "Raw and honest from the heart!" writing. No bullshit. Real insights into the career and skills of a modern software engineer.
Want to become a true senior engineer? Take ownership, have autonomy, and be a force multiplier on your team. The Senior Engineer Mindset ebook can help 👉 swizec.com/senior-mindset. These are the shifts in mindset that unlocked my career.
Curious about Serverless and the modern backend? Check out Serverless Handbook, for frontend engineers 👉 ServerlessHandbook.dev
Want to Stop copy pasting D3 examples and create data visualizations of your own? Learn how to build scalable dataviz React components your whole team can understand with React for Data Visualization
Did someone amazing share this letter with you? Wonderful! You can sign up for my weekly letters for software engineers on their path to greatness, here: swizec.com/blog
By the way, just in case no one has told you it yet today: I love and appreciate you for who you are ❤️