postcss-rem-to-responsive-pixel

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

• Rewrite with typescript and well tested.
• Support Postcss7 and Postcss8 !
• TransformUnit Support px and rpx ! (for those miniprogram developers who use my tailwindcss-miniprogram-preset)

Install

$ yarn add -D postcss-rem-to-responsive-pixel

Usage

// postcss 8:
require('postcss-rem-to-responsive-pixel')
// postcss 7:
require('postcss-rem-to-responsive-pixel/postcss7')

When you use tailwindcss to write your website or miniprogram(Chinese Developer knows LOL) , the default unit is rem, so sometimes we have to transform our unit to px or rpx.

this plugin use like postcss-rem-to-pixel, all options are compatible !

Thanks to the author of postcss-rem-to-pixel and postcss-pxtorem.

if you use with tailwindcss and tailwindcss-miniprogram-preset

you may should close the rem2rpx in this preset:

// tailwind.config.js
const { createPreset } = require('tailwindcss-miniprogram-preset')
module.exports = {
  presets: [
    createPreset({
      rem2rpx: false,
    }),
  ],
}

and set below options:

// postcss.config.js
module.exports = {
  plugins: [
    require('autoprefixer'),
    require('tailwindcss'),
    require('postcss-rem-to-responsive-pixel')({
      rootValue: 32,
      propList: ['*'],
      transformUnit: 'rpx',
    }),
  ],
}

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;
}

options

Type: Object | Null
Default:

{
    rootValue: 16,
    unitPrecision: 5,
    propList: ['font', 'font-size', 'line-height', 'letter-spacing'],
    selectorBlackList: [],
    replace: true,
    mediaQuery: false,
    minRemValue: 0 ,
    exclude: undefined,
    transformUnit: 'px'
}

• 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.
• exclude (String, Regexp, Function) The file path to ignore and leave as px.
  • If value is string, it checks to see if file path contains the string.
    • 'exclude' will match \project\postcss-pxtorem\exclude\path
  • If value is regexp, it checks to see if file path matches the regexp.
    • /exclude/i will match \project\postcss-pxtorem\exclude\path
  • If value is function, you can use exclude function to return a true and the file will be ignored.
    • the callback will pass the file path as a parameter, it should returns a Boolean result.
    • function (file) { return file.indexOf('exclude') !== -1; }
• transformUnit (px or rpx) The transform output unit.

Use with postcss.config.js

// postcss.config.js
module.exports = {
  plugins: [
    // for example
    // require('autoprefixer'),
    // require('tailwindcss'),
    require('postcss-rem-to-responsive-pixel')({
      rootValue: 32,
      propList: ['*'],
      transformUnit: 'rpx',
    }),
  ],
}

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
}