postcss-rpxtorem 

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

Fork postcss-pxtorem

背景：小程序转换其他项目（vue等）时，需要把rpx转换成rem

Install

``shell
$ npm install postcss-rpxtorem --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.

rpx

关于rpx的描述:
> rpx（responsive pixel）: 可以根据屏幕宽度进行自适应。规定屏幕宽为750rpx。如在 iPhone6 上，屏幕宽度为375px，共有750个物理像素，则750rpx = 375px = 750物理像素，1rpx = 0.5px = 1物理像素。
> | 设备 | rpx换算px (屏幕宽度/750) | px换算rpx (750/屏幕宽度)
> | ------------- |:-------------:| -----:|
> | iPhone5 | 1rpx = 0.42px | 1px = 2.34rpx
> | iPhone6 | 1rpx = 0.5px | 1px = 2rpx

$3

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

`css
// input
h1 {
margin: 0 0 20rpx;
font-size: 32px;
line-height: 1.2;
letter-spacing: 1px;
}

// output
h1 {
margin: 0 0 1.25rem;
font-size: 2rem;
line-height: 1.2;
letter-spacing: 0.0625rem;
}
`

$3

`js
var fs = require('fs');
var postcss = require('postcss');
var rpxtorem = require('postcss-rpxtorem');
var css = fs.readFileSync('main.css', 'utf8');
var options = {
replace: false
};
var processedCss = postcss(rpxtorem(options)).process(css).css;

fs.writeFile('main-rem.css', processedCss, function (err) {
if (err) {
throw err;
}
console.log('Rem file written.');
});
`

$3

Type: Object | Null
Default:
`js
{
rootValue: 16,
unitPrecision: 5,
propList: ['*'],
selectorBlackList: [],
replace: true,
mediaQuery: false,
minPixelValue: 0
}
`

- rootValue (Number) The root element font size.
- 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.




$3

`js
var gulp = require('gulp');
var postcss = require('gulp-postcss');
var autoprefixer = require('autoprefixer');
var rpxtorem = require('postcss-rpxtorem');

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

var processors = [
autoprefixer({
browsers: 'last 1 version'
}),
rpxtorem({
replace: false
})
];

return gulp.src(['build/css/*/.css'])
.pipe(postcss(processors))
.pipe(gulp.dest('build/css'));
});
`

$3

Currently, the easiest way to have a single property ignored is to use a capital in the pixel unit declaration.

`css
// rpx is converted to rem
.convert {
font-size: 16rpx; // converted to 1rem
}

// Px or PX is ignored by postcss-pxtorem but still accepted by browsers
.ignore {
border: 1rPx solid; // ignored
border-width: 2RPX; // ignored
}
``