postcss-rem-to-pixel

A plugin for PostCSS that generates px units from rem units.

Install

$ npm install postcss-rem-to-pixel --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 match background-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 match body but not .body
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
}

jesstech / postcss-rem-to-pixel Goto Github PK