CSS MQPacker
Pack same CSS media query rules into one using PostCSS
SYNOPSIS
A well componentized CSS file may have same media queries that can merge:
.foo {
width: 240px;
}
@media screen and (min-width: 768px) {
.foo {
width: 576px;
}
}
.bar {
width: 160px;
}
@media screen and (min-width: 768px) {
.bar {
width: 384px;
}
}
This PostCSS plugin packs exactly same media queries:
.foo {
width: 240px;
}
.bar {
width: 160px;
}
@media screen and (min-width: 768px) {
.foo {
width: 576px;
}
.bar {
width: 384px;
}
}
INSTALL
$ npm install css-mqpacker
USAGE
Of course, this package can be used as PostCSS plugin:
#!/usr/bin/env node
"use strict";
const fs = require("fs");
const postcss = require("postcss");
postcss([
require("autoprefixer-core")(),
require("css-mqpacker")()
]).process(fs.readFileSync("from.css", "utf8")).then(function (result) {
console.log(result.css);
});
It is a recommended way to use this tool.
As standard Node.js package
This package is also a Node.js module. For exmaple, you can read from.css
,
process its content, and output processed CSS to STDOUT:
#!/usr/bin/env node
"use strict";
const fs = require("fs");
const mqpacker = require("css-mqpacker");
cosole.log(mqpacker.pack(fs.readFileSync("from.css", "utf8"), {
from: "from.css",
map: {
inline: false
},
to: "to.css"
}).css);
As CLI Program
This package also installs a command line interface.
$ node ./node_modules/.bin/mqpacker --help
Usage: mqpacker [options] INPUT [OUTPUT]
Description:
Pack same CSS media query rules into one using PostCSS
Options:
-s, --sort Sort “min-width” queries.
--sourcemap Create source map file.
-h, --help Show this message.
--version Print version information.
Use a single dash for INPUT to read CSS from standard input.
Examples:
$ mqpacker fragmented.css
$ mqpacker fragmented.css > packed.css
When PostCSS failed to parse INPUT, CLI shows a CSS parse error in GNU error format instead of Node.js stack trace.
The --sort
option does not currently support a custom function.
If you install this package in global, CLI will be available somewhere in the
$PATH
.
OPTIONS
sort
By default, CSS MQPacker pack and order media queries as they are defined (the
“first win” algorithm). If you want to sort media queries automatically,
pass sort: true
to this module.
postcss([
mqpacker({
sort: true
})
]).process(css);
Currently, this option only supports min-width
queries with specific units
(ch
, em
, ex
, px
, and rem
). If you want to do more, you need to create
your own sorting function and pass it to this module like this:
postcss([
mqpacker({
sort: function (a, b) {
return a.localeCompare(b);
}
})
]).process(css);
In this example, all your media queries will sort by A-Z order.
This sorting function is directly passed to Array#sort()
method of an array of
all your media queries.
API
pack(css, [options])
Packs media queries in css
.
The second argument is optional. The options
are:
- options mentioned above
- the second argument of PostCSS’s
process()
method
You can specify both at the same time.
const fs = require("fs");
const mqpacker = require("css-mqpacker");
const result = mqpacker.pack(fs.readFileSync("from.css", "utf8"), {
from: "from.css",
map: {
inline: false
},
sort: true,
to: "to.css"
});
fs.writeFileSync("to.css", result.css);
fs.writeFileSync("to.css.map", result.map);
NOTES
With CSS MQPacker, the processed CSS is always valid CSS, but you and your website user will get unexpected results. This section explains how CSS MQPacker works and what you should keep in mind.
CSS Cascading Order
CSS MQPacker changes rulesets’ order. This means the processed CSS will have an unexpected cascading order. For example:
@media (min-width: 640px) {
.foo {
width: 300px;
}
}
.foo {
width: 400px;
}
Becomes:
.foo {
width: 400px;
}
@media (min-width: 640px) {
.foo {
width: 300px;
}
}
.foo
is always 400px
with original CSS. With processed CSS, however, .foo
is 300px
if viewport is wider than 640px
.
This does not occur on small project. However, this could occur frequently on large project. For example, if you want to override a CSS framework (like Bootstrap) component declaration, your whole CSS code will be something similar to above example. To avoid this problem, you should pack only CSS you write, and then concaenate with a CSS framework.
The “First Win” Algorithm
CSS MQPacker is implemented with the “first win” algorithm. This means:
.foo {
width: 10px;
}
@media (min-width: 640px) {
.foo {
width: 150px;
}
}
.bar {
width: 20px;
}
@media (min-width: 320px) {
.bar {
width: 200px;
}
}
@media (min-width: 640px) {
.bar {
width: 300px;
}
}
Becomes:
.foo {
width: 10px;
}
.bar {
width: 20px;
}
@media (min-width: 640px) {
.foo {
width: 150px;
}
.bar {
width: 300px;
}
}
@media (min-width: 320px) {
.bar {
width: 200px;
}
}
This breaks cascading order of .bar
, and .bar
will be displayed in 200px
instead of 300px
even if a viewport wider than 640px
.
I suggest defining a query order on top of your CSS:
@media (min-width: 320px) { /* Wider than 320px */ }
@media (min-width: 640px) { /* Wider than 640px */ }
If you use simple min-width
queries only, the sort
option can help.
Multiple Classes
CSS MQPacker works only with CSS. This may break CSS applying order to an elements that have multiple classes. For example:
@media (min-width: 320px) {
.foo {
width: 100px;
}
}
@media (min-width: 640px) {
.bar {
width: 200px;
}
}
@media (min-width: 320px) {
.baz {
width: 300px;
}
}
Becomes:
@media (min-width: 320px) {
.foo {
width: 100px;
}
.baz {
width: 300px;
}
}
@media (min-width: 640px) {
.bar {
width: 200px;
}
}
The result looks good. However, if an HTML element has class="bar baz"
and
viewport width larger than 640px
, that element width
incorrectly set to
200px
instead of 300px
. This problem cannot be resolved only with CSS, so be
careful!