What is postcss-calc?
The postcss-calc npm package is a PostCSS plugin that reduces CSS calc() function to the maximum, whenever it's possible. It simplifies calculations in CSS files and optimizes them during the build process, making the final CSS file lighter and easier for browsers to parse.
What are postcss-calc's main functionalities?
Simplification of calc expressions
This feature allows the simplification of calc expressions in CSS, reducing them to their simplest form. For example, if you have a calculation based on CSS custom properties or simple arithmetic, postcss-calc can compute these values at build time, resulting in cleaner and more efficient CSS.
css
.post {
--gap: 20px;
padding: calc(var(--gap) * 2);
}
/* becomes */
.post {
padding: 40px;
}
Optimization of complex calculations
For more complex calculations that cannot be fully simplified without context (like viewport sizes or percentages), postcss-calc optimizes the expression to ensure it's as efficient as possible without altering the intended result.
css
.banner {
width: calc(100% - 80px);
}
/* becomes */
.banner {
width: calc(100% - 80px);
}
Other packages similar to postcss-calc
cssnano
cssnano is a modular CSS minifier that includes functionalities similar to postcss-calc as part of its optimizations. It uses PostCSS to analyze and rewrite CSS files, reducing their size. While cssnano includes a broader range of optimizations, postcss-calc focuses specifically on the optimization of calc() functions.
postcss-custom-properties
postcss-custom-properties is another PostCSS plugin that allows you to use CSS custom properties (variables) in your stylesheets. It can transform these properties into static values, similar to how postcss-calc simplifies calc() expressions. However, it focuses on variables rather than calculations.
postcss-calc 
PostCSS plugin to reduce calc()
.
This plugin reduce calc()
references whenever it's possible.
This can be particularly useful with the postcss-custom-properties plugin.
Note: When multiple units are mixed together in the same expression, the calc()
statement is left as is, to fallback to the w3c calc() feature.
Installation
$ npm install postcss-calc
Usage
var fs = require("fs")
var postcss = require("postcss")
var calc = require("postcss-calc")
var css = fs.readFileSync("input.css", "utf8")
var output = postcss()
.use(calc())
.process(css)
.css
Example (with postcss-custom-properties enabled as well):
var fs = require("fs")
var postcss = require("postcss")
var customProperties = require("postcss-custom-properties")
var calc = require("postcss-calc")
var css = fs.readFileSync("input.css", "utf8")
var output = postcss()
.use(customProperties())
.use(calc())
.process(css)
.css
Using this input.css
:
:root {
--main-font-size: 16px;
}
body {
font-size: var(--main-font-size);
}
h1 {
font-size: calc(var(--main-font-size) * 2);
height: calc(100px - 2em);
}
you will get:
body {
font-size: 16px
}
h1 {
font-size: 32px;
height: calc(100px - 2em)
}
Checkout tests for more examples.
Options
precision
(default: 5
)
Allow you to definine the precision for decimal numbers.
var out = postcss()
.use(calc({precision: 10}))
.process(css)
.css
preserve
(default: false
)
Allow you to preserve calc() usage in output so browsers will handle decimal precision themselves.
var out = postcss()
.use(calc({preserve: true}))
.process(css)
.css
Contributing
Work on a branch, install dev-dependencies, respect coding style & run tests before submitting a bug fix or a feature.
$ git clone https://github.com/postcss/postcss-calc.git
$ git checkout -b patch-1
$ npm install
$ npm test