node-css-mqpacker

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:

``css
.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 tool packs exactly same media queries:

`css
.foo {
width: 240px;
}

.bar {
width: 160px;
}

@media screen and (min-width: 768px) {
.foo {
width: 576px;
}
.bar {
width: 384px;
}
}
`

INSTALL
-------

$ echo @hail2u:registry=https://npm.pkg.github.com >> .npmrc
$ npm install --save-dev @hail2u/css-mqpacker

If you or your team member does not have GitHub account, you can install
directly from the GitHub repository:

$ npm install --save-dev github:hail2u/node-css-mqpacker#

should be replaced with one of the [available tags][1].


USAGE
-----

Of course, this package can be used as PostCSS plugin:

`javascript
const fs = require("fs");
const postcss = require("postcss");

postcss([
require("@hail2u/css-mqpacker")()
]).process(fs.readFileSync("from.css", "utf8")).then(function (result) {
console.log(result.css);
});
`

It is a recommended way to use this tool.

$3

This package is also a Node.js module. For example, you can read from.css,
process its content, and output processed CSS to STDOUT:

`javascript
const fs = require("fs");
const mqpacker = require("@hail2u/css-mqpacker");

console.log(mqpacker.pack(fs.readFileSync("from.css", "utf8"), {
from: "from.css",
map: {
inline: false
},
to: "to.css"
}).css);
`

$3

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.


OPTIONS
-------

$3

By default, CSS MQPacker pack and order media queries as they are defined ([the
“first win” algorithm][2]). If you want to sort media queries automatically,
pass sort: true to this module.

`javascript
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:

`javascript
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
---

$3

Packs media queries in css.

The second argument is optional. The options are:

- [options][3] mentioned above
- the second argument of [PostCSS’s process() method][4]

You can specify both at the same time.

`javascript
const fs = require("fs");
const mqpacker = require("@hail2u/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.

$3

CSS MQPacker changes rulesets’ order. This means the processed CSS will have an
unexpected cascading order. For example:

`css
@media (min-width: 640px) {
.foo {
width: 300px;
}
}

.foo {
width: 400px;
}
`

Becomes:

`css
.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 concatenate with a CSS framework.

$3

CSS MQPacker is implemented with the “first win” algorithm. This means:

`css
.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:

`css
.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:

`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][5] can help.

$3

CSS MQPacker works only with CSS. This may break CSS applying order to an
elements that have multiple classes. For example:

`css
@media (min-width: 320px) {
.foo {
width: 100px;
}
}

@media (min-width: 640px) {
.bar {
width: 200px;
}
}

@media (min-width: 320px) {
.baz {
width: 300px;
}
}
`

Becomes:

`css
@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!

LICENSE
-------

MIT

[1]: https://github.com/hail2u/node-css-mqpacker/tags
[2]: #the-first-win-algorithm
[3]: #options
[4]: http://api.postcss.org/global.html#processOptions
[5]: #sort