Josh Comeau's blog

Glassy headers have become a core part of the “slick startup” UI toolkit, but they’re all missing that final 10% that really makes it shine. In this tutorial, you’ll learn how to create the most realistic lush frosted glass anywhere on the internet.

Lots of exciting new features have been landing in CSS recently, and it can be tough trying to figure out if they’re safe to use or not. We might know that a feature is available for 92% of users, but is that sufficient? Where do we draw the line? In this blog post, I’ll share the framework I use for deciding whether or not to use a modern CSS...

It’s been a couple of years since container queries started landing in browsers… so why isn’t anyone using them? It turns out that container queries are kinda tricky; they’re not as straightforward as media queries. In this tutorial, we’ll break it all down and make sense of them, so that you can start using them in your work.

I recently launched a brand new version of this blog, and in this post, I share how it’s built! We’ll examine the tech stack and see how all of the pieces fit together, as well as dig into some of the details to see how they work.

Of all the latest and greatest CSS features, the “:has” pseudo-class wasn’t exactly at the top of my wishlist. Once I started using it, however, I kept discovering incredible things I could do with it. It’s now become a core part of my toolkit! In this blog post, I'll show you some practical real-world problems I solved using “:has”, as well as...

The “Promises” API is a surprisingly tricky part of modern JavaScript. Without the right context, it doesn’t make much sense at all! In this tutorial, you’ll build an intuition for how Promises work by getting a deeper understanding of JavaScript and its limitations.

useDeferredValue is one of the most underrated React hooks. It allows us to dramatically improve the performance of our applications in certain contexts. I recently used it to solve a gnarly performance problem on this blog, and in this tutorial, I'll show you how! ⚡

You can’t make an omelette without cracking a few eggs, and when the core React team unveiled their vision for the future of React, some of my favourite libraries got scrambled 😅. In this blog post, we’re going to explore the compatibility issues between React Server Components and CSS-in-JS libraries like styled-components. You’ll understand...

Back in the day, centering an element was one of the trickiest things in CSS. As the language has evolved, we’ve been given lots of new tools we can use… But how do we pick the best option? When do we use Flexbox, or CSS Grid, or something else? Let's dig into it.

CSS Grid is an incredibly powerful tool for building layouts on the web, but like all powerful tools, there's a significant learning curve. In this tutorial, we'll build a mental model for how CSS Grid works and how we can use it effectively. I'll share the biggest 💡 lightbulb moments I've had in my own learning journey.

One of the most commonly-misunderstood operators is Modulo (%). In this tutorial, we'll unpack exactly what this little bugger does, and learn how it can help us solve practical problems.

This year, the React team unveiled something they've been quietly researching for years: an official way to run React components exclusively on the server. This is a significant paradigm shift, and it's caused a whole lot of confusion in the React community. In this tutorial, we'll explore this new world, and build an intuition for how it works,...

Happy Pride month! In this tutorial, I'll share a handful of my favourite animation tricks. You'll learn how to build an animated wavy pride flag using CSS keyframes and linear gradients. We'll also see how to make it dynamic using React. 🏳️‍🌈

The “const” keyword in JavaScript is used to create constants, variables that can't change. Curiously, though, we do seem to be able to edit objects and arrays that are created using “const”. In this tutorial, we're going to dig into the incredibly-important distinction between “assignment” and “mutation” in JavaScript.

Large language models like GPT-4 are becoming increasingly capable, at an alarming rate. Within a couple of years, we won't need developers any more! …Or at least, that's the narrative going viral on Twitter. I'm much more optimistic about what these AI advancements mean for the future of software development.

I used to teach React at a local coding bootcamp, and I noticed that students kept getting tripped up by the same handful of things. In this article, we're going to go through 9 of the most dastardly gotchas. I'll show you how to solve these common problems, so you can avoid a lot of potential frustration!

As developers, we don't like working with forms, but they're a critical part of most web applications! In this tutorial, you'll learn exactly how to wire up all of the different form controls in React. Never forget how to data-bind a checkbox or radio button again!

CSS gives us so many options when it comes to expressing color—we can use hex codes, rgb, hsl, and more. Which option should we choose? This turns out to be a surprisingly important decision! In this article, we'll take a tour of color formats in CSS, and see which option will serve us best.

When we truly learn the secrets of the Flexbox layout mode, we can build absolutely incredible things. Fluid layouts that stretch and shrink without arbitrary breakpoints. In this action-packed interactive tutorial, we'll pop the hood on the Flexbox algorithm and learn how to do remarkable things with it. ✨

No developer blog or technical documentation site is complete without an interactive code playground. The CodeSandbox team recently released a wonderful tool called Sandpack, to help us create these live-updating code editors. In this tutorial, I'll show you how I use it on this blog.

What's the deal with these two hooks?! Lots of devs find them confusing, for a whole host of reasons. In this tutorial, we'll dig deep and understand what they do, why they're useful, and how to get the most out of them.

In React, we don't update the DOM directly, we tell React what we want the DOM to look like, and React tackles the rest. But how exactly does it do this? In this tutorial, we'll unpack exactly when and why React re-renders, and how we can use this information to optimize the performance of our React apps.

One of the most foundational things to understand about JavaScript is that programs are made up of statements, and statements have slots for expressions. In this blog post, we'll dig into how these two structures work, and see how building an intuition about this can help us solve practical problems.

If you've ever had the misfortune of being tasked with building a template for HTML emails, you know it's tricky business! In this blog post, I share the approach I took to build responsive, client-friendly emails without a single tag.

“Should I use pixels or rems?”. In this comprehensive blog post, we'll answer this question once and for all. You'll learn about the accessibility implications, and how to determine the best unit to use in any scenario.

As developers, it can be tempting to grab a pre-styled UI framework like Material UI or Bootstrap. Seems like a great way to outsource design and save a bunch of time, right? In my experience, this is an unrealistic expectation, and things don’t quite work out that way.

If you want to learn a modern JavaScript framework like React or Angular, you better be familiar with the terminal! So many frameworks and tools assume that you're proficient with it, without ever explaining it. This blog post is your missing manual, covering all of the most important fundamentals.

As front-end developers, we often learn CSS by focusing on individual properties. Instead, we should focus on how the language uses those properties to calculate layouts. In this blog post, we'll pop the hood on CSS and see how the language is structured, and how to learn it effectively.

How should we structure components and other files in our React apps? I've iterated my way to a solution I'm really happy with. In this blog post, I'll share how it works, what the tradeoffs are, and how I mitigate them.

Have you ever noticed that gradients tend to look a little gray and washed-out in the middle? This happens because of a mathematical quirk with RGB colors. Fortunately, we can work around this quirk, and create beautiful, lush, saturated gradients.

I have a set of baseline CSS styles that come with me from project to project. In the past, I'd use a typical CSS reset, but times have changed, and I believe I have a better set of global styles!

In order to create lush, realistic shadows in CSS, we need to use multiple layers and colors. How do we come up with all of the parameters, though? I've built a tool that'll help.

When I look around the web, most of the shadows I see are fuzzy grey boxes. It doesn't have to be this way, though! CSS gives us the tools to create rich, lush, lifelike shadows. In this tutorial, I'll show you how.

CSS keyframe animations are incredibly flexible and powerful, but they’re also a bit weird. In this deep-dive tutorial, we'll learn how CSS keyframes work from the ground up, and see how to use them to build high-quality animations.

The “transform” property is such a powerful part of the CSS language! In this blog post, we'll take a deep look at this property and see some of the nifty things it can do.

As software developers, we're always learning new things; it's practically the whole gig! If we can learn to quickly pick up new languages/frameworks/tools, we'll become so much more effective at our job. It's sort of a superpower.

For so many React devs, styled-components seems kinda magical. It isn't at all clear how it uses traditional CSS features under-the-hood, and that lack of clarity can cause real problems when things go awry. In this post, we'll learn exactly how styled-components works by building our own mini-version.

An in-depth look at the technical stack behind this very blog! We'll see how I use Next's API routes to implement my hit and like counters, how I use MDX to add interaction and customization, and how I organize my codebase, among others.

Every action we take on the web starts with a button click, and yet most buttons are ho-hum and uninspired. In this tutorial, we'll build an animated 3D button with HTML and CSS that sparks joy.

I know so many super-talented developers who share the same achilles heel: CSS. Instead of trying to “outrun” CSS, this article explores why leaning in and going deeper can be a tremendous boon for your development life and your career.

The z-index property can be a tricky little bugger. Sometimes, no matter how much you crank up the number, the element never rises to the top! In this article, we explore stacking contexts, and see how they can thwart our efforts to use z-index. We'll also learn how to use this mechanism to our advantage.

This comprehensive guide shows how to use CSS transitions! A back-to-basics look at the fundamental building blocks we need to create microinteractions and other animations.

styled-components is a wonderfully powerful styling library for React, and over the years I've learned a lot about how to use it effectively. This article shares my personal “best practices”.

The 90s web gave us many delightful things: web rings, guestbooks, “under construction” animations, and spacer GIFs. In this article, we'll see how I use a Spacer component to solve common layout problems, and why it's often a great tool for the job in the modern web.

Next allows you to do server-side data-fetching, but what happens when that data needs to change on the client? This brief tutorial shows how to re-fetch the props without doing a full server reload.

“Margin collapse” has a dastardly reputation, one of the trickier parts of CSS. Fortunately, it gets a lot easier once you learn a few rules! In this tutorial, we take a deep dive into the governing principles, and learn how to use them to our advantage.

An in-depth tutorial that teaches how to create one of the most adorable interactions I've ever created. We'll learn how to use React components and hooks to abstract behaviours, and see how to design the perfect API. Even if you're not into animations, I think you'll find it interesting!

Is it possible to create an implementation of a design that matches to-the-pixel? Well, not really, but that shouldn't discourage us! In this article, I'll show how I became designers' best friend by leveraging a series of tricks to get my implementation looking near-pixel-perfect.

Earlier this year, I lost the ability to use a keyboard and mouse for extended periods. Fortunately, this wasn't as catastrophic as it sounds! This article chronicles my experience using adaptive tools like dictation and eye-tracking as my primary mechanisms for writing code.

Certain layouts are surprisingly dastardly. On the modern web, one of the most common layouts is also one of the trickiest. In this tutorial, I break down how to build the "full-bleed" layout using CSS Grid.

Of all the little tips and techniques I've picked up over the years about animation, spring physics remains one of the most powerful and flexible. In this tutorial, we'll learn how to harness their power to build fluid, organic transitions.

Learn how to set up an ideal workflow for debugging your development server on your iPhone. This may not be the most exciting topic I've written about, but it's probably one of the most useful!

In this dazzling tutorial, we'll see how to build an animated component. Wrap it around text or images and watch them twinkle! This neat trick is a perfect way to emphasize positive or exciting things.

Speaking at conferences is equal parts exciting and terrifying. This article is a behind-the-scenes look at what the experience is like, and shares tips for getting started as a conference speaker.

I really love animation, but not everybody does. In fact, it can make some people literally sick! In this tutorial, we'll see how to ensure that we respect user preferences, and create animations that can be disabled.

In our community, it's so common for developer projects to be open-source. I'm breaking with this trend for my blog, but I have good reasons! In this article, I'll share my reasoning, as well as a workaround in case you _really_ want to see the source. If you're considering whether a project should be open-source or not, I hope you'll find it...

Dark Mode has become common enough that it's a user expectation. And yet, creating the perfect dark mode with a statically-built site/app is deceptively tricky. In this in-depth tutorial, we'll see how to build the perfect, flicker-free, customizable theming solution for React/Next.js apps.

CSS variables are *really* cool, and they're incredibly powerful when it comes to React! This tutorial shows how we can use them with React to create dynamic themes. We'll see how to get the most out of CSS-in-JS tools like styled-components, and how our mental frame around media queries has been wrong all along.

Styling an ordered list can be surprisingly tricky; there's no way to get at that bullet! In this tutorial, we'll see a handy trick using CSS counters that lets us style ordered lists without breaking proper semantics.

By and large, using the web is a visual experience. This is in terrible contrast to mobile apps, which interact with three of our human senses (sight, sound, and touch, through haptic feedback). I just released a library to make it easy to add sound to your React app, and I make the case that you should consider using it!

A look at how hundreds of developers got their start in the industry despite not having a Computer Science or Software Engineering degree. We'll sort responses into 6 categories, and detail strategies that you can use to ensure you capture the attention of potential employers!

A surprisingly-common misconception can lead to big rendering issues that are difficult to debug. This deep-dive tutorial examines how React and Gatsby can be used to pre-render content, and how we can work around the constraints to build dynamic, personalized web apps.

A common thing in React development is that we want to store a bit of React state in localStorage, and re-initialize from that value on the next page-load. This quick tutorial shows you how we can build a custom hook that does exactly this!

How we work with design can have a tremendous impact on our overall output, and yet we don't always treat it as very important. A look at how collaborating with design can supercharge our own productivity.

If you've ever tried to animate a gradient, you've been met with a harsh reality—it isn't possible. At least, it wasn't! In this tutorial, we'll leverage bleeding-edge browser features to animate ANY CSS property, including background gradients, using CSS Houdini, CSS variables, and React.

As remote work becomes increasingly popular, I am frequently asked how to get started. This article shares everything I know about landing that first remote gig.

I've spent half of my career working remotely. This post chronicles those experiences, giving a real-world window into what it's like to work fully-remote as a software engineer.

As engineers, it can be really satisfying for us to implement clever, terse solutions to problems, relying on advanced tricks and techniques. As a result, we often write code that is hostile and inaccessible to the junior folks on our team. This article makes the case that we should strive to write simple, accessible code, using the dumb old...

In this post, we'll explore a technique we can use to "fold" a DOM node, like folding a letter in real-life. On that journey, we'll learn a lot about 3D transforms and CSS animation techniques!

A deep dive into Bézier curves in React. We'll look at how to build dynamic effects such as scroll-to-flatten using SVG path instructions, and how to architect our components for maximum readability and reusability.

An in-depth look at the surprisingly complicated problem of animating the transition when two items in a list swap positions.