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https://github.com/cuth/postcss-pxtorem

Convert pixel units to rem (root em) units using PostCSS
https://github.com/cuth/postcss-pxtorem

pixel-units postcss rem-units

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Convert pixel units to rem (root em) units using PostCSS

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# postcss-pxtorem [![NPM version](https://badge.fury.io/js/postcss-pxtorem.svg)](http://badge.fury.io/js/postcss-pxtorem)



A plugin for [PostCSS](https://github.com/ai/postcss) that generates rem units from pixel units.



## Install



```shell

$ npm install postcss postcss-pxtorem --save-dev

```



## Usage



Pixels are the easiest unit to use (*opinion*). The only issue with them is that they don't let browsers change the default font size of 16. This script converts every px value to a rem from the properties you choose to allow the browser to set the font size.



### Input/Output



*With the default settings, only font related properties are targeted.*



```css

// input

h1 {

    margin: 0 0 20px;

    font-size: 32px;

    line-height: 1.2;

    letter-spacing: 1px;

}



// output

h1 {

    margin: 0 0 20px;

    font-size: 2rem;

    line-height: 1.2;

    letter-spacing: 0.0625rem;

}

```



### Example



```js

var fs = require('fs');

var postcss = require('postcss');

var pxtorem = require('postcss-pxtorem');

var css = fs.readFileSync('main.css', 'utf8');

var options = {

    replace: false

};

var processedCss = postcss(pxtorem(options)).process(css).css;



fs.writeFile('main-rem.css', processedCss, function (err) {

  if (err) {

    throw err;

  }

  console.log('Rem file written.');

});

```



### options



Type: `Object | Null`  

Default:

```js

{

    rootValue: 16,

    unitPrecision: 5,

    propList: ['font', 'font-size', 'line-height', 'letter-spacing', 'word-spacing'],

    selectorBlackList: [],

    replace: true,

    mediaQuery: false,

    minPixelValue: 0,

    exclude: /node_modules/i

}

```



- `rootValue` (Number | Function) Represents the root element font size or returns the root element font size based on the [`input`](https://api.postcss.org/Input.html) parameter

- `unitPrecision` (Number) The decimal numbers to allow the REM units to grow to.

- `propList` (Array) The properties that can change from px to rem.

    - 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 px.

    - 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 px to be converted in media queries.

- `minPixelValue` (Number) Set the minimum pixel 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; }`

- `unit` (String) Set the default unit to convert, default is `px`.



### Use with gulp-postcss and autoprefixer



```js

var gulp = require('gulp');

var postcss = require('gulp-postcss');

var autoprefixer = require('autoprefixer');

var pxtorem = require('postcss-pxtorem');



gulp.task('css', function () {



    var processors = [

        autoprefixer({

            browsers: 'last 1 version'

        }),

        pxtorem({

            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 pixel unit declaration.



```css

// `px` is converted to `rem`

.convert {

    font-size: 16px; // converted to 1rem

}



// `Px` or `PX` is ignored by `postcss-pxtorem` but still accepted by browsers

.ignore {

    border: 1Px solid; // ignored

    border-width: 2PX; // ignored

}

```