postcss-rem-to-pixel-next
A plugin for PostCSS that generates px units from rem units.
Acknowledgements
This project is an updated version of the original postcss-rem-to-pixel plugin, which was created by jesstech. All credit for the original concept and implementation goes to them.
I have updated the plugin to utilize the new PostCSS 8 API.
Install
$ npm i postcss-rem-to-pixel-next --save-dev
Usage
Sometimes you need to include a third-party css file that uses rems. Great pracitice! Unless you can't afford to change your body font-size just for some vendor. This script converts every rem value to a px value from the properties you choose using a default font size of 16px.
Input/Output
With the default settings, only font related properties are targeted.
// input
h1 {
margin: 0 0 20px;
font-size: 2rem;
line-height: 1.2;
letter-spacing: 0.0625rem;
}
// output
h1 {
margin: 0 0 20px;
font-size: 32px;
line-height: 1.2;
letter-spacing: 1px;
}
Example
var fs = require("fs");
var postcss = require("postcss");
var remToPx = require("postcss-rem-to-pixel");
var css = fs.readFileSync("main.css", "utf8");
var options = {
replace: false,
};
var processedCss = postcss(remToPx(options)).process(css).css;
fs.writeFile("main-px.css", processedCss, function (err) {
if (err) {
throw err;
}
console.log("Rem file written.");
});
options
Type: Object | Null
Default:
{
rootValue: 16,
unitPrecision: 5,
propList: ['font', 'font-size', 'line-height', 'letter-spacing'],
selectorBlackList: [],
replace: true,
mediaQuery: false,
minRemValue: 0
}
-
rootValue
(Number) The root element font size. -
unitPrecision
(Number) The decimal precision px units are allowed to use, floored (rounding down on half). -
propList
(Array) The properties that can change from rem to px.- Values need to be exact matches.
- Use wildcard
*
to enable all properties. Example:['*']
- Use
*
at the start or end of a word. (['*position*']
will matchbackground-position-y
) - Use
!
to not match a property. Example:['*', '!letter-spacing']
- Combine the "not" prefix with the other prefixes. Example:
['*', '!font*']
-
selectorBlackList
(Array) The selectors to ignore and leave as rem.- If value is string, it checks to see if selector contains the string.
-
['body']
will match.body-class
-
- If value is regexp, it checks to see if the selector matches the regexp.
-
[/^body$/]
will matchbody
but not.body
-
- If value is string, it checks to see if selector contains the string.
-
replace
(Boolean) replaces rules containing rems instead of adding fallbacks. -
mediaQuery
(Boolean) Allow rem to be converted in media queries. -
minRemValue
(Number) Set the minimum rem value to replace.
Use with gulp-postcss and autoprefixer
var gulp = require("gulp");
var postcss = require("gulp-postcss");
var autoprefixer = require("autoprefixer");
var remToPx = require("postcss-rem-to-pixel");
gulp.task("css", function () {
var processors = [
autoprefixer({
browsers: "last 1 version",
}),
remToPx({
replace: false,
}),
];
return gulp
.src(["build/css/**/*.css"])
.pipe(postcss(processors))
.pipe(gulp.dest("build/css"));
});
A message about ignoring properties
Currently, the easiest way to have a single property ignored is to use a capital in the rem unit declaration.
// `rem` is converted to `px`
.convert {
font-size: 1rem; // converted to 16px
}
// `Rem` or `REM` is ignored by `postcss-rem-to-pixel` but still accepted by browsers
.ignore {
border: 1Rem solid; // ignored
border-width: 2REM; // ignored
}