postcss-transform-unit

本项目从项目{postcss-pxtorpx-pro(https://www.npmjs.com/package/postcss-pxtorpx-pro )}基础上修改而来， 转换默认是从rem单位为rpx，但是经过本次配置后，可以从任意单位转换到任意单位的，并提供了转换函数，支持指定黑名单prop。

This repo is fork from postcss-pxtorpx-pro, but more powerful than it. This plugin can transform pixels unit to any unit theoretically, which default transform to rpx unit.

rpx is the unit make for developing mini-program, see @wxa

Install

$ npm install postcss-transform-unit --save-dev

Usage

像素是web开发中最常用的单位，但在做响应式页面开发之时稍显无力，开发者需要编写大量适配代码。故在移动端开发中我们常搭配rem, vw等单位使用，而在开发各类小程序中，我们又常用rpx取代vw。

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.

h1 {
    margin: 0 0 20px;
    font-size: 32px;
    line-height: 1.2;
    letter-spacing: 1px;
}

h1 { 
  margin: 0 0 40rpx; 
  font-size: 64rpx; 
  line-height: 1.2; 
  letter-spacing: 2rpx; 
}

Example

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

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

options

Type: Object | Null
Default:

{
  // 转换前的单位
  beforeUnit: 'rem',
  // 转化的单位
  unit: 'rpx',
  // 单位精度
  unitPrecision: 5,
  // 不需要处理的css选择器
  selectorBlackList: [],
  // 不需要转化的css属性
  propBlackList: [], 
  // 直接修改px，还是新加一条css规则
  replace: true,
  // 是否匹配媒介查询的px
  mediaQuery: false,
  // 需要转化的最小的pixel值，低于该值的px单位不做转化
  minPixelValue: 0,
  // 不处理的文件
  exclude: null,
  // 转化函数
  // 默认设计稿按照750宽，2倍图的出
  transform: (x) => 2*x
}

• beforeUnit(String) Unit before conversion. default rem.
• unit(String) The unit transform to. default rpx.
• unitPrecision (Number) The decimal numbers to allow the rpx units to grow to.
• transform (Function) function to transform pixels to other unit. default (x) => 2 * x.
• propBlackList (Array) The properties that can change from px to rpx.
  • 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 rpxs 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-pxtorpx\exclude\path
  • If value is regexp, it checks to see if file path matches the regexp.
    • /exclude/i will match \project\postcss-pxtorpx\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; }

Use with gulp-postcss and autoprefixer

// 可以结合 vue.config.js 以及 webpack来使用，但是需要自己写个中间转换loader 来执行
const PostcssTransformUnit = require('postcss-transform-unit'),
  postcss = require('postcss'),
  unitTransformOptions = {
    transform: (x) => 100 * x
  }

/**
 * @description 进行css默认单位的转换 rem => rpx
 * @param source 源代码
 * @returns {string} 返回转换后的代码
 */
function loader(source) {
  // 版本一：本loader初衷是结合uniapp进行单位转换的 如果是微信环境的话 直接转换 反之返回源代码
  return process.env.UNI_PLATFORM === 'mp-weixin' ? postcss(PostcssTransformUnit({
    replace: true,
    ...unitTransformOptions
  })).process(source).css : source
  
  // 版本二：如果不需要环境配置 每次都需要转换的话 可以直接返回
  return postcss(PostcssTransformUnit({
    replace: true,
    ...unitTransformOptions
  })).process(source).css
}

module.exports = loader

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.

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

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

REF

本插件是从任意单位 到 任意单位 所以取名是transform-unit