Do you want to turn boring data into visually stimulating charts that will engage your website visitors? Some things can be communicated better using charts. And how do you build charts in a way that saves you time to focus on running your business? This is where chart plugins for WordPress and WooCommerce come in.…
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TikTok quickly took over the world with its trendy video-based content format. With over 800 million active users, TikTok is more than just about dancing videos and memes. It’s now a platform for marketing. TikTok is now bigger than Reddit, Twitter, and even Snapchat. As a result, everyone from small personal brands to big corporate…
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HTML5 Canvas and SVG are both standards-based HTML5 technologies that you can use to create amazing graphics and visual experiences. The question I’m asking in this article is the following: Should it matter which one you use in your project? In other words, are there any use cases for preferring HTML5 Canvas over SVG?First, let’s spend a few words introducing HTML5 Canvas and SVG.
What Is HTML5 Canvas?
Here’s how the WHATWG specification introduces the canvas element:
The canvas element provides scripts with a resolution-dependent bitmap canvas, which can be used for rendering graphs, game graphics, art, or other visual images on the fly.
In other words, the tag exposes a surface where you can create and manipulate rasterized images pixel by pixel using a JavaScript programmable interface.
Here’s a basic code sample:
See the Pen Basic Canvas Shape Demo by SitePoint (@SitePoint)on CodePen.
The HTML:
The JavaScript:
const canvas = document.getElementById(‘myCanvas’);
const context = canvas.getContext(‘2d’);
context.fillStyle = ‘#c00’;
context.fillRect(10, 10, 100, 100);
You can take advantage of the HTML5 Canvas API methods and properties by getting a reference to the 2D context object. In the example above, I’ve drawn a simple red square, 100 x 100 pixels in size, placed 10px from the left and 10px from the top of the drawing surface.
Being resolution-dependent, images you create on may lose quality when enlarged or displayed on Retina Displays.
Drawing simple shapes is just the tip of the iceberg. The HTML5 Canvas API allows you to draw arcs, paths, text, gradients, etc. You can also manipulate your images pixel by pixel. This means that you can replace one color with another in certain areas of the graphics, you can animate your drawings, and even draw a video onto the canvas and change its appearance.
What Is SVG?
SVG stands for Scalable Vector Graphics. According to the specification:
SVG is a language for describing two-dimensional graphics. As a standalone format or when mixed with other XML, it uses the XML syntax. When mixed with HTML5, it uses the HTML5 syntax. …
SVG drawings can be interactive and dynamic. Animations can be defined and triggered either declaratively (i.e., by embedding SVG animation elements in SVG content) or via scripting.
SVG is an XML file format designed to create vector graphics. Being scalable has the advantage of letting you increase or decrease a vector image while maintaining its crispness and high quality. (This can’t be done with HTML5 Canvas-generated images.)
Here’s the same red square (previously created with HTML5 Canvas) this time drawn using SVG:
See the Pen Basic SVG Shape by SitePoint (@SitePoint)on CodePen.
Red rectangle shape
You can do with SVG most of the stuff you can do with Canvas — such as drawing shapes and paths, gradients, patterns, animation, and so on. However, these two technologies work in fundamentally different ways. Unlike a Canvas-based graphic, SVG has a DOM, and as such both CSS and JavaScript have access to it. For example, you can change the look and feel of an SVG graphic using CSS, animate its nodes with CSS or JavaScript, make any of its parts respond to a mouse or a keyboard event the same as a . As it will become clearer in the following sections, this difference plays a significant part when you need to make a choice between Canvas and SVG for your next project.
It’s crucial to distinguish between immediate mode and retained mode. HTML5 Canvas is an example of the former, SVG of the latter.
Immediate mode means that, once your drawing is on the canvas, the canvas stops keeping track of it. In other words you, as the developer, you need to work out the commands to draw objects, create and maintain the model or scene of what the final output should look like, and specify what needs to be updated. The browser’s Graphics API simply communicates your drawing commands to the browser, which then executes them.
SVG uses the retained approach, where you simply issue your drawing instructions of what you want to display on the screen, and the browser’s Graphics API creates an in-memory model or scene of the final output and translates it into drawing commands for your browser.
Being an immediate graphics system, Canvas hasn’t got a DOM, or Document Object Model. With Canvas, you draw your pixels and the system forgets all about them, thereby cutting down on the extra memory needed to maintain an internal model of your drawing. With SVG, each object you draw gets added to the browser’s internal model, which makes your life as a developer somewhat easier, but at some costs in terms of performance.
On the basis of the distinction between immediate and retained mode, as well as other specific characteristics of Canvas and SVG respectively, it’s possible to outline some cases where using one technology over the other might better serve your project’s goals.
HTML5 Canvas: Pros and Cons
The HTML5 Canvas specification clearly recommends that authors should not use the element where they have other more suitable means available to them.
For instance, for a graphically rich element, the best tools are HTML and CSS, not (and neither is SVG, by the way). Dr Abstract, creator and founder of the Zim JS canvas framework, confirms this view as he writes:
The DOM and the DOM frameworks are good at displaying information and in particular text information. In comparison, the canvas is a picture. Text can be added to the canvas and it can be made responsive, but the text cannot be readily selected or searched as on the DOM. Long scrolling pages of text or text and images is an excellent use of the DOM. The DOM is great for social media sites, forums, shopping, and all the information apps we are used to. — “When to Use a JavaScript Canvas Library or Framework”
So, that’s a clear-cut example of when not to use . But when is a good option?
This tweet by Sarah Drasner summarizes some major pros and cons of canvas features and capabilities, which can help us to work out some use cases for this powerful technology:
I had this slide in a lot of talks and workshops over the years: pic.twitter.com/4K0C7mNzg2
— Sarah Drasner (@sarah_edo) October 2, 2019
You can view the image from the tweet here.
What HTML5 Canvas Can Be Great For
Alvin Wan has benchmarked Canvas and SVG in terms of performance both in relation to the number of objects being drawn and in relation to the size of the objects or the canvas itself. He states his results as follows:
In sum, the overhead of DOM rendering is more poignant when juggling hundreds if not thousands of objects; in this scenario, Canvas is the clear winner. However, both the canvas and SVG are invariant to object sizes. Given the final tally, the canvas offers a clear win in performance.
Drawing on what we know about Canvas, especially its excellent performance at drawing lots of objects, here are some possible scenarios where it might be appropriate, and even preferable to SVG.
Games and Generative Art
For graphics-intensive, highly interactive games, as well as for generative art, Canvas is generally the way to go.
Ray Tracing
Ray tracing is a technique for creating 3D graphics.
Ray tracing can be used to hydrate an image by tracing the path of light through pixels in an image plane and simulating the effects of its encounters with virtual objects. … The effects achieved by ray tracing, … range from … creating realistic images from otherwise simple vector graphics to applying photo-like filters to remove red-eye. — SVG vs Canvas: how to choose, Microsoft Docs.
If you’re curious, here’s a raytracer application in action by Mark Webster.
However, although HTML5 Canvas is definitely better suited to the task than SVG could ever be, it doesn’t necessarily follow that ray tracing is best executed on a element. In fact, the strain on the CPU could be quite considerable, to the point that your browser could stop responding.
Drawing a Significant Number of Objects on a Small Surface
Another example is a scenario where your application needs to draw a significant number of objects on a relatively small surface — such as non-interactive real-time data visualizations like graphical representations of weather patterns.
The above image is from this MSDN article, which was part of my research for this piece.
Pixel Replacement in Videos
As demonstrated in this HTML5 Doctor article, another example where Canvas would be appropriate is when replacing a video background color with a different color, another scene, or image.
What HTML5 Canvas Isn’t So Great For
On the other hand, there are a number of cases where Canvas might not be the best choice compared to SVG.
Scalability
Most scenarios where scalability is a plus are going to be better served using SVGs rather than Canvas. High-fidelity, complex graphics like building and engineering diagrams, organizational charts, biological diagrams, etc., are examples of this.
When drawn using SVG, enlarging the images or printing them preserves all the details to a high level of quality. You can also generate these documents from a database, which makes the XML format of SVG highly suited to the task.
Also, these graphics are often interactive. Think about seat maps when you’re booking your plane ticket online as an example, which makes them a great use case for a retained graphics system like SVG.
That said, with the help of some great libraries like CreateJS and Zim (which extends CreateJS), developers can relatively quickly integrate mouse events, hit tests, multitouch gestures, drag and drop capabilities, controls, and more, to their Canvas-based creations.
Accessibility
Although there are steps you can take to make a Canvas graphic more accessible — and a good Canvas library like Zim could be helpful here to speed up the process — canvas doesn’t shine when it comes to accessibility. What you draw on the canvas surface is just a bunch of pixels, which can’t be read or interpreted by assistive technologies or search engine bots. This is another area where SVG is preferable: SVG is just XML, which makes it readable by both humans and machines.
No Reliance on JavaScript
If you don’t want to use JavaScript in your application, then Canvas isn’t your best friend. In fact, the only way you can work with the element is with JavaScript. Conversely, you can draw SVG graphics using a standard vector editing program like Adobe Illustrator or Inkscape, and you can use pure CSS to control their appearance and perform eye-catching, subtle animations and microinteractions.
Combining HTML5 Canvas and SVG for Advanced Scenarios
There are cases where your application can get the best of both worlds by combining HTML5 Canvas and SVG. For instance, a Canvas-based game could implement sprites from SVG images generated by a vector editing program, to take advantage of the scalability and reduced download size compared to a PNG image. Or a paint program could have its user interface designed using SVG, with an embedded element, which could be used for drawing.
Finally, a powerful library like Paper.js makes it possible to script vector graphics on top of HTML5 Canvas, thereby offering devs a convenient way of working with both technologies.
Conclusion
In this article, I’ve explored some key features of both HTML5 Canvas and SVG to help you decide which technology might be most suited suited to particular tasks.
What’s the answer?
Chris Coyier agrees with Benjamin De Cock, as the latter tweets:
One extremely basic way to answer it is “use canvas when you cannot use svg” (where “cannot” might mean animating thousands of objects, manipulating each pixel individually, etc.). To put it another way, SVG should be your default choice, canvas your backup plan.
— Benjamin De Cock (@bdc) October 2, 2019
Dr Abstract offers a long list of things that are best built using Canvas, including interactive logos and advertising, interactive infographics, e-learning apps, and much more.
In my view, there aren’t any hard and fast rules for when it’s best to use Canvas instead of SVG. The distinction between immediate and retained mode points to HTML5 Canvas as being the undisputed winner when it comes to building things like graphic-intensive games, and to SVG as being preferable for things like flat images, icons and UI elements. However, in between there’s room for HTML5 Canvas to expand its reach, especially considering what the various powerful Canvas libraries could bring to the table. Not only do they make it easier to work with both technologies in the same graphic work, but they also make it so that some hard-to-implement features in a native Canvas-based project — like interactive controls and events, responsiveness, accessibility features, and so on — could now be at most developers’ fingertips, which leaves the door open to the possibility of ever more interesting uses of HTML5 Canvas.
HTML5 Canvas and SVG are both standards-based HTML5 technologies that you can use to create amazing graphics and visual experiences. The question I’m asking in this article is the following: Should it matter which one you use in your project? In other words, are there any use cases for preferring HTML5 Canvas over SVG?First, let’s spend a few words introducing HTML5 Canvas and SVG.
What Is HTML5 Canvas?
Here’s how the WHATWG specification introduces the canvas element:
The canvas element provides scripts with a resolution-dependent bitmap canvas, which can be used for rendering graphs, game graphics, art, or other visual images on the fly.
In other words, the tag exposes a surface where you can create and manipulate rasterized images pixel by pixel using a JavaScript programmable interface.
Here’s a basic code sample:
See the Pen Basic Canvas Shape Demo by SitePoint (@SitePoint)on CodePen.
The HTML:
The JavaScript:
const canvas = document.getElementById(‘myCanvas’);
const context = canvas.getContext(‘2d’);
context.fillStyle = ‘#c00’;
context.fillRect(10, 10, 100, 100);
You can take advantage of the HTML5 Canvas API methods and properties by getting a reference to the 2D context object. In the example above, I’ve drawn a simple red square, 100 x 100 pixels in size, placed 10px from the left and 10px from the top of the drawing surface.
Being resolution-dependent, images you create on may lose quality when enlarged or displayed on Retina Displays.
Drawing simple shapes is just the tip of the iceberg. The HTML5 Canvas API allows you to draw arcs, paths, text, gradients, etc. You can also manipulate your images pixel by pixel. This means that you can replace one color with another in certain areas of the graphics, you can animate your drawings, and even draw a video onto the canvas and change its appearance.
What Is SVG?
SVG stands for Scalable Vector Graphics. According to the specification:
SVG is a language for describing two-dimensional graphics. As a standalone format or when mixed with other XML, it uses the XML syntax. When mixed with HTML5, it uses the HTML5 syntax. …
SVG drawings can be interactive and dynamic. Animations can be defined and triggered either declaratively (i.e., by embedding SVG animation elements in SVG content) or via scripting.
SVG is an XML file format designed to create vector graphics. Being scalable has the advantage of letting you increase or decrease a vector image while maintaining its crispness and high quality. (This can’t be done with HTML5 Canvas-generated images.)
Here’s the same red square (previously created with HTML5 Canvas) this time drawn using SVG:
See the Pen Basic SVG Shape by SitePoint (@SitePoint)on CodePen.
Red rectangle shape
You can do with SVG most of the stuff you can do with Canvas — such as drawing shapes and paths, gradients, patterns, animation, and so on. However, these two technologies work in fundamentally different ways. Unlike a Canvas-based graphic, SVG has a DOM, and as such both CSS and JavaScript have access to it. For example, you can change the look and feel of an SVG graphic using CSS, animate its nodes with CSS or JavaScript, make any of its parts respond to a mouse or a keyboard event the same as a . As it will become clearer in the following sections, this difference plays a significant part when you need to make a choice between Canvas and SVG for your next project.
It’s crucial to distinguish between immediate mode and retained mode. HTML5 Canvas is an example of the former, SVG of the latter.
Immediate mode means that, once your drawing is on the canvas, the canvas stops keeping track of it. In other words you, as the developer, you need to work out the commands to draw objects, create and maintain the model or scene of what the final output should look like, and specify what needs to be updated. The browser’s Graphics API simply communicates your drawing commands to the browser, which then executes them.
SVG uses the retained approach, where you simply issue your drawing instructions of what you want to display on the screen, and the browser’s Graphics API creates an in-memory model or scene of the final output and translates it into drawing commands for your browser.
Being an immediate graphics system, Canvas hasn’t got a DOM, or Document Object Model. With Canvas, you draw your pixels and the system forgets all about them, thereby cutting down on the extra memory needed to maintain an internal model of your drawing. With SVG, each object you draw gets added to the browser’s internal model, which makes your life as a developer somewhat easier, but at some costs in terms of performance.
On the basis of the distinction between immediate and retained mode, as well as other specific characteristics of Canvas and SVG respectively, it’s possible to outline some cases where using one technology over the other might better serve your project’s goals.
HTML5 Canvas: Pros and Cons
The HTML5 Canvas specification clearly recommends that authors should not use the element where they have other more suitable means available to them.
For instance, for a graphically rich element, the best tools are HTML and CSS, not (and neither is SVG, by the way). Dr Abstract, creator and founder of the Zim JS canvas framework, confirms this view as he writes:
The DOM and the DOM frameworks are good at displaying information and in particular text information. In comparison, the canvas is a picture. Text can be added to the canvas and it can be made responsive, but the text cannot be readily selected or searched as on the DOM. Long scrolling pages of text or text and images is an excellent use of the DOM. The DOM is great for social media sites, forums, shopping, and all the information apps we are used to. — “When to Use a JavaScript Canvas Library or Framework”
So, that’s a clear-cut example of when not to use . But when is a good option?
This tweet by Sarah Drasner summarizes some major pros and cons of canvas features and capabilities, which can help us to work out some use cases for this powerful technology:
I had this slide in a lot of talks and workshops over the years: pic.twitter.com/4K0C7mNzg2
— Sarah Drasner (@sarah_edo) October 2, 2019
You can view the image from the tweet here.
What HTML5 Canvas Can Be Great For
Alvin Wan has benchmarked Canvas and SVG in terms of performance both in relation to the number of objects being drawn and in relation to the size of the objects or the canvas itself. He states his results as follows:
In sum, the overhead of DOM rendering is more poignant when juggling hundreds if not thousands of objects; in this scenario, Canvas is the clear winner. However, both the canvas and SVG are invariant to object sizes. Given the final tally, the canvas offers a clear win in performance.
Drawing on what we know about Canvas, especially its excellent performance at drawing lots of objects, here are some possible scenarios where it might be appropriate, and even preferable to SVG.
Games and Generative Art
For graphics-intensive, highly interactive games, as well as for generative art, Canvas is generally the way to go.
Ray Tracing
Ray tracing is a technique for creating 3D graphics.
Ray tracing can be used to hydrate an image by tracing the path of light through pixels in an image plane and simulating the effects of its encounters with virtual objects. … The effects achieved by ray tracing, … range from … creating realistic images from otherwise simple vector graphics to applying photo-like filters to remove red-eye. — SVG vs Canvas: how to choose, Microsoft Docs.
If you’re curious, here’s a raytracer application in action by Mark Webster.
However, although HTML5 Canvas is definitely better suited to the task than SVG could ever be, it doesn’t necessarily follow that ray tracing is best executed on a element. In fact, the strain on the CPU could be quite considerable, to the point that your browser could stop responding.
Drawing a Significant Number of Objects on a Small Surface
Another example is a scenario where your application needs to draw a significant number of objects on a relatively small surface — such as non-interactive real-time data visualizations like graphical representations of weather patterns.
The above image is from this MSDN article, which was part of my research for this piece.
Pixel Replacement in Videos
As demonstrated in this HTML5 Doctor article, another example where Canvas would be appropriate is when replacing a video background color with a different color, another scene, or image.
What HTML5 Canvas Isn’t So Great For
On the other hand, there are a number of cases where Canvas might not be the best choice compared to SVG.
Scalability
Most scenarios where scalability is a plus are going to be better served using SVGs rather than Canvas. High-fidelity, complex graphics like building and engineering diagrams, organizational charts, biological diagrams, etc., are examples of this.
When drawn using SVG, enlarging the images or printing them preserves all the details to a high level of quality. You can also generate these documents from a database, which makes the XML format of SVG highly suited to the task.
Also, these graphics are often interactive. Think about seat maps when you’re booking your plane ticket online as an example, which makes them a great use case for a retained graphics system like SVG.
That said, with the help of some great libraries like CreateJS and Zim (which extends CreateJS), developers can relatively quickly integrate mouse events, hit tests, multitouch gestures, drag and drop capabilities, controls, and more, to their Canvas-based creations.
Accessibility
Although there are steps you can take to make a Canvas graphic more accessible — and a good Canvas library like Zim could be helpful here to speed up the process — canvas doesn’t shine when it comes to accessibility. What you draw on the canvas surface is just a bunch of pixels, which can’t be read or interpreted by assistive technologies or search engine bots. This is another area where SVG is preferable: SVG is just XML, which makes it readable by both humans and machines.
No Reliance on JavaScript
If you don’t want to use JavaScript in your application, then Canvas isn’t your best friend. In fact, the only way you can work with the element is with JavaScript. Conversely, you can draw SVG graphics using a standard vector editing program like Adobe Illustrator or Inkscape, and you can use pure CSS to control their appearance and perform eye-catching, subtle animations and microinteractions.
Combining HTML5 Canvas and SVG for Advanced Scenarios
There are cases where your application can get the best of both worlds by combining HTML5 Canvas and SVG. For instance, a Canvas-based game could implement sprites from SVG images generated by a vector editing program, to take advantage of the scalability and reduced download size compared to a PNG image. Or a paint program could have its user interface designed using SVG, with an embedded element, which could be used for drawing.
Finally, a powerful library like Paper.js makes it possible to script vector graphics on top of HTML5 Canvas, thereby offering devs a convenient way of working with both technologies.
Conclusion
In this article, I’ve explored some key features of both HTML5 Canvas and SVG to help you decide which technology might be most suited suited to particular tasks.
What’s the answer?
Chris Coyier agrees with Benjamin De Cock, as the latter tweets:
One extremely basic way to answer it is “use canvas when you cannot use svg” (where “cannot” might mean animating thousands of objects, manipulating each pixel individually, etc.). To put it another way, SVG should be your default choice, canvas your backup plan.
— Benjamin De Cock (@bdc) October 2, 2019
Dr Abstract offers a long list of things that are best built using Canvas, including interactive logos and advertising, interactive infographics, e-learning apps, and much more.
In my view, there aren’t any hard and fast rules for when it’s best to use Canvas instead of SVG. The distinction between immediate and retained mode points to HTML5 Canvas as being the undisputed winner when it comes to building things like graphic-intensive games, and to SVG as being preferable for things like flat images, icons and UI elements. However, in between there’s room for HTML5 Canvas to expand its reach, especially considering what the various powerful Canvas libraries could bring to the table. Not only do they make it easier to work with both technologies in the same graphic work, but they also make it so that some hard-to-implement features in a native Canvas-based project — like interactive controls and events, responsiveness, accessibility features, and so on — could now be at most developers’ fingertips, which leaves the door open to the possibility of ever more interesting uses of HTML5 Canvas.
To prepare for our future image effects, we’re going to set up a card component that has a large image at the top followed by a headline and description. The common problem with this setup is that we may not always have perfect control over what the image is, and more importantly to our layout,…
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https://designdrizzle.com/the-application-of-augmented-reality-in-web-design/
Designing a giveaway or contest on Instagram can be fun, increase engagement, and help boost your presence online. But it’s more than just asking people to tag a friend to win a prize. A great giveaway takes planning, a prize that’s worth people’s time, and an understanding of the rules to maintain the integrity of…
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A business brochure is an important marketing asset that can help get your business noticed. You can hand them out during networking events as well as leave them in local cafes’ to raise awareness about your products and services. In this post, we’ve rounded up the best business brochure templates that are easy to edit…
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Let’s talk shadows in web design. Shadows add texture, perspective, and emphasize the dimensions of objects. In web design, using light and shadow can add physical realism and can be used to make rich, tactile interfaces. Take the landing page below. It is for cycling tours in Iceland. Notice the embellished drop shadow of the…
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Web developers love the Sass CSS preprocessor. According to the Sass opinions in the State of CSS Survey, every developer knows what it is, 89% use it regularly, and 88% have high satisfaction.Many web bundlers include Sass processing, but you may also be using PostCSS without realizing it. PostCSS is primarily known for its Autoprefixer plugin, which automatically adds -webkit, -moz, and -ms vendor prefixes to CSS properties when required. Its plugin system means it can do so much more … such as compiling .scss files without having to use the Sass compiler.
This tutorial explains how to create a custom CSS preprocessor which compiles Sass syntax and supplements it with further features. It’s ideal for anyone with specific CSS requirements who knows a little Node.js.
Quick Start
An example PostCSS project can be cloned from GitHub. It requires Node.js, so run npm install to fetch all dependencies.
Compile the demonstration src/scss/main.scss source code to build/css/main.css using:
npm run css:dev
Auto-compile whenever files are changed using:
npm run css:watch
Then exit watching by pressing Ctrl | Cmd + C in the terminal.
Both options also create a source map at build/css/main.css.map, which references the original source files in the developer tools.
Production-level minified CSS without a source map can be compiled using:
npm run css:build
Refer to the README.md file for further information.
Should You Replace Sass with PostCSS?
There’s nothing wrong with the Sass compiler, but consider the following factors.
Module Dependencies
The latest Dart version of Sass can be installed globally using the Node.js npm package manager:
npm install -g sass
Compile Sass .scss code with:
sass [input.scss] [output.css]
Source maps are automatically generated (–no-source-map will switch them off) or –watch can be added to auto-compile source files when they change.
The latest version of Sass requires less than 5MB of installation space.
PostCSS should require fewer resources and a basic Sass-like compiler with auto-prefixing, and minification needs less than 1MB of space. In reality, your node_modules folder will expand to more than 60MB and increase rapidly as more plugins are added. This is mostly npm installing other dependencies. Even though PostCSS may not use them, it can’t be considered as a lightweight alternative.
However, if you’re already using PostCSS for Autoprefixer or other purposes, Sass may not be necessary.
Processing Speed
The slow, Ruby-based Sass compiler has long gone and the latest edition uses a compiled Dart runtime. It’s fast.
PostCSS is pure JavaScript and, while benchmarks will differ, it can be three times slower at compiling the same source code.
However, this speed difference will be less noticeable if you’re already running PostCSS after Sass. A two-stage process can be slower than using PostCSS alone, since much of its work involves tokenizing CSS properties.
Customization
The Sass language includes a large set of features including variables, nesting, partials, mixins, and more. There are downsides:
You cannot easily add new features.
Perhaps you’d like an option convert HSLA colors to RGB. It may be possible to write a custom function, but other requirements will be impossible — such as inlining an SVG as a background image.
You can’t easily restrict the feature set.
Perhaps you’d prefer your team not to use nesting or @extend. Linting rules will help, but they won’t stop Sass compiling valid .scss files.
PostCSS is considerably more configurable.
On its own, PostCSS does nothing. Processing functionality requires one or more of the many plugins available. Most perform a single task, so if you don’t want nesting, don’t add a nesting plugin. If necessary, you can write your own plugins in a standard JavaScript module that can harness the power of Node.js.
Install PostCSS
PostCSS can be used with webpack, Parcel, Gulp.js, and other build tools, but this tutorial shows how to run it from the command line.
If necessary, initialize a new Node.js project with npm init. Set up PostCSS by installing the following modules for basic .scss parsing with plugins for partials, variables, mixins, nesting, and auto-prefixing:
npm install –save-dev postcss postcss-cli postcss-scss postcss-advanced-variables postcss-nested autoprefixer
Like the example project, PostCSS and its plugins are installed locally. This is a practical option if your projects are likely to have differing compilation requirements.
Note: PostCSS can only be run from a JavaScript file, but the postcss-cli module provides a wrapper that can be called from the command line. The postcss-scss module allows PostCSS to read .scss files but doesn’t transform them.
Autoprefixer Configuration
Autoprefixer uses browserslist to determine which vendor prefixes are required according to your list of supported browsers. It’s easiest to define this list as a “browserslist” array in package.json. The following example adds vendor prefixes where any browser has at least 2% market share:
“browserslist”: [
” > 2%”
],
Your First Build
You’ll typically have a single root Sass .scss file which imports all required partial/component files. For example:
@import ‘_variables’;
@import ‘_reset’;
@import ‘components/_card’;
Compilation can be started by running npx postcss, followed by the input file, an –output file, and any required options. For example:
npx postcss ./src/scss/main.scss
–output ./build/css/main.css
–env development
–map
–verbose
–parser postcss-scss
–use postcss-advanced-variables postcss-nested autoprefixer
This command:
parses ./src/scss/main.scss
outputs to ./build/css/main.css
sets the NODE_ENV environment variable to development
outputs an external source map file
sets verbose output and error messages
sets the postcss-scss Sass parser, and
uses the plugins postcss-advanced-variables, postcss-nested, and autoprefixer to handle partials, variables, mixins, nesting, and auto-prefixing
Optionally, you could add –watch to auto-compile when .scss files are modified.
Create a PostCSS Configuration File
The command line quickly becomes unwieldy for longer lists of plugins. You can define it as an npm script, but a PostCSS configuration file is an easier option that offers additional possibilities.
PostCSS configuration files are JavaScript module files named postcss.config.js and typically stored in the project’s root directory (or whichever directory you run PostCSS from). The module must export a single function:
module.exports = cfg = > {
};
It’s passed a cfg object with properties set by the postcss command. For example:
{
cwd: ‘/home/name/postcss-demo’,
env: ‘development’,
options: {
map: undefined,
parser: undefined,
syntax: undefined,
stringifier: undefined
},
file: {
dirname: ‘/home/name/postcss-demo/src/scss’,
basename: ‘main.scss’,
extname: ‘.scss’
}
}
You can examine these properties and react accordingly — for example, determine whether you’re running in development mode and processing a .scss input file:
module.exports = cfg = > {
const
dev = cfg.env === ‘development’,
scss = cfg.file.extname === ‘.scss’;
};
The function must return an object with property names matching the postcss-cli command line options. The following configuration file replicates the long quick start command used above:
module.exports = cfg = > {
const
dev = cfg.env === ‘development’,
scss = cfg.file.extname === ‘.scss’;
return {
map: dev ? { inline: false } : false,
parser: scss ? ‘postcss-scss’ : false,
plugins: [
require(‘postcss-advanced-variables’)(),
require(‘postcss-nested’)(),
require(‘autoprefixer’)()
]
};
};
PostCSS can now be run using a shorter command:
npx postcss ./src/scss/main.scss
–output ./build/css/main.css
–env development
–verbose
Here are some things to note:
–verbose is optional: it’s not set in postcss.config.js.
Sass syntax parsing is only applied when the input is a .scss file. Otherwise, it defaults to standard CSS.
A source map is only output when –env is set to development.
–watch can still be added for auto-compilation.
If you’d prefer postcss.config.js to be in another directory, it can be referenced with the –config option — such as –config /mycfg/. In the example project, the configuration above is located in config/postcss.config.js. It’s referenced by running npm run css:basic, which calls:
npx postcss src/scss/main.scss
–output build/css/main.css
–env development
–verbose
–config ./config/
Adding Further Plugins
The following sections provide examples of PostCSS plugins which either parse additional .scss syntax or provide processing beyond the scope of the Sass compiler.
Use Design Tokens
Design Tokens are a technology-agnostic way to store variables such as corporation-wide fonts, colors, spacing, etc. You could store token name–value pairs in a JSON file:
{
“font-size”: “16px”,
“font-main”: “Roboto, Oxygen-Sans, Ubuntu, sans-serif”,
“lineheight”: 1.5,
“font-code”: “Menlo, Consolas, Monaco, monospace”,
“lineheight-code”: 1.2,
“color-back”: “#f5f5f5”,
“color-fore”: “#444”
}
Then reference them in any web, Windows, macOS, iOS, Linux, Android, or other application.
Design tokens are not directly supported by Sass, but a JavaScript object with a variables property holding name–value pairs can be passed to the existing postcss-advanced-variables PostCSS plugin:
module.exports = cfg = > {
const variables = require(‘./tokens.json’);
const
dev = cfg.env === ‘development’,
scss = cfg.file.extname === ‘.scss’;
return {
map: dev ? { inline: false } : false,
parser: scss ? ‘postcss-scss’ : false,
plugins: [
require(‘postcss-advanced-variables’)({ variables }),
require(‘postcss-nested’)(),
require(‘autoprefixer’)()
]
};
};
The plugin converts all values to global Sass $variables which can be used in any partial. A fallback value can be set to ensure a variable is available even when it’s missing from tokens.json. For example:
$color-back: #fff !default;
Token variables can then be referenced in any .scss file. For example:
body {
font-family: $font-main;
font-size: $font-size;
line-height: $lineheight;
color: $color-fore;
background-color: $color-back;
}
In the example project, a token.json file is defined, which is loaded and used when running npm run css:dev.
Add Sass Map Support
Sass Maps are key–value objects. The map-get function can look up values by name.
The following example defines media query breakpoints as a Sass map with a respond mixin to fetch a named value:
$breakpoint: (
‘small’: 36rem,
‘medium’: 50rem,
‘large’: 64rem
);
@mixin respond($bp) {
@media (min-width: map-get($breakpoint, $bp)) {
@content;
}
}
Default properties and media query modifications can then be defined in the same selector. For example:
main {
width: 100%;
@include respond(‘medium’) {
width: 40em;
}
}
Which compiles to CSS:
main {
width: 100%;
}
@media (min-width: 50rem) {
main {
width: 40em
}
}
The postcss-map-get plugin adds Sass map processing. Install it with:
npm install –save-dev postcss-map-get
And update the postcss.config.js configuration file:
module.exports = cfg = > {
const variables = require(‘./tokens.json’);
const
dev = cfg.env === ‘development’,
scss = cfg.file.extname === ‘.scss’;
return {
map: dev ? { inline: false } : false,
parser: scss ? ‘postcss-scss’ : false,
plugins: [
require(‘postcss-advanced-variables’)({ variables }),
require(‘postcss-map-get’)(),
require(‘postcss-nested’)(),
require(‘autoprefixer’)()
]
};
};
Add Media Query Optimization
Since we’ve added media queries, it would be useful to combine and sort them into mobile-first order. For example, the following CSS:
@media (min-width: 50rem) {
main {
width: 40em;
}
}
@media (min-width: 50rem) {
#menu {
width: 30em;
}
}
can be merged to become:
@media (min-width: 50rem) {
main {
width: 40em;
}
#menu {
width: 30em;
}
}
This isn’t possible in Sass, but can be achieved with the PostCSS postcss-sort-media-queries plugin. Install it with:
npm install –save-dev postcss-sort-media-queries
Then add it to postcss.config.js:
module.exports = cfg = > {
const variables = require(‘./tokens.json’);
const
dev = cfg.env === ‘development’,
scss = cfg.file.extname === ‘.scss’;
return {
map: dev ? { inline: false } : false,
parser: scss ? ‘postcss-scss’ : false,
plugins: [
require(‘postcss-advanced-variables’)({ variables }),
require(‘postcss-map-get’)(),
require(‘postcss-nested’)(),
require(‘postcss-sort-media-queries’)(),
require(‘autoprefixer’)()
]
};
};
Add Asset Processing
Asset management is not available in Sass, but postcss-assets makes it easy. The plugin resolves CSS image URLs, adds cache-busting, defines image dimensions, and inlines files using base64 notation. For example:
#mybackground {
background-image: resolve(‘back.png’);
width: width(‘back.png’);
height: height(‘back.png’);
background-size: size(‘back.png’);
}
compiles to:
#mybackground {
background-image: url(‘/images/back.png’);
width: 600px;
height: 400px;
background-size: 600px 400px;
}
Install the plugin with:
npm install –save-dev postcss-assets
Then add it to postcss.config.js. In this case, the plugin is instructed to locate images in the src/images/ directory:
module.exports = cfg = > {
const variables = require(‘./tokens.json’);
const
dev = cfg.env === ‘development’,
scss = cfg.file.extname === ‘.scss’;
return {
map: dev ? { inline: false } : false,
parser: scss ? ‘postcss-scss’ : false,
plugins: [
require(‘postcss-advanced-variables’)({ variables }),
require(‘postcss-map-get’)(),
require(‘postcss-nested’)(),
require(‘postcss-sort-media-queries’)(),
require(‘postcss-assets’)({
loadPaths: [‘src/images/’]
}),
require(‘autoprefixer’)()
]
};
};
Add Minification
cssnano sets the standard for CSS minification. Minification can take more processing time than other plugins, so it can be applied in production only.
Install cssnano with:
npm install –save-dev cssnano
Then add it to postcss.config.js. In this case, minification only occurs when NODE_ENV is set to anything other than development:
module.exports = cfg = > {
const variables = require(‘./tokens.json’);
const
dev = cfg.env === ‘development’,
scss = cfg.file.extname === ‘.scss’;
return {
map: dev ? { inline: false } : false,
parser: scss ? ‘postcss-scss’ : false,
plugins: [
require(‘postcss-advanced-variables’)({ variables }),
require(‘postcss-map-get’)(),
require(‘postcss-nested’)(),
require(‘postcss-sort-media-queries’)(),
require(‘postcss-assets’)({
loadPaths: [‘src/images/’]
}),
require(‘autoprefixer’)(),
dev ? null : require(‘cssnano’)()
]
};
};
Setting –env to prodution triggers minification (and removes the source map):
npx postcss ./src/scss/main.scss
–output ./build/css/main.css
–env prodution
–verbose
In the example project, production CSS can be compiled by running npm run css:build.
Progress to PostCSS?
PostCSS is a powerful and configurable tool that can compile .scss files and enhance (or restrict) the standard Sass language. If you’re already using PostCSS for Autoprefixer, you may be able to remove the Sass compiler entirely while retaining the syntax you love.
Further links: