Ember CLI Postcss

Use postcss to process your css with a large selection of plug-ins.

Installation

ember install ember-cli-postcss

Usage

The add-on can be used in two ways:

on individual files, referred to as “compile”
on all CSS files, referred to as “filter”

Note: it’s possible to use both compile and filter.

Compile

This step will look for either app.css or <project-name>.css in your styles directory. Additional files to be processed can be defined in the output paths configuration object for your application:

const app = new EmberApp(defaults, {
  outputPaths: {
    app: {
      html: 'index.html',
      css: {
        'app': '/assets/app.css',
        'print': '/assets/print.css'
      }
    }
  }
}

Filter

This step will run at the end of the build process on all CSS files, including the merged vendor.css file and any CSS imported into the Broccoli tree by add-ons.

Files can be white-listed and/or black-listed by using the respective include and exclude options. Each accepts an array of file globs, which are then passed on to Broccoli Funnel. An example can be seen in the sample configuration below.

Configuring Plug-ins

There are two steps to setting up postcss with ember-cli-postcss:

install and require the node modules for any plug-ins
provide the node module and plug-in options as a postcssOptions object in ember-cli-build.js

The postcssOptions object should have a “compile” and/or “filter” property, which will have the properties enabled and plugins, which is an array of objects that contain a module property and an options property:

Browser Targets

Some postcss plug-ins, like autoprefixer, allow you to configure which browsers to target for transpilation. When using Ember CLI >= 2.13.0, the browser targets configuration found in the file config/targets.js will be added to each plug-in’s options (as options.browsers). This browser list can be overwritten on a plug-in by plug-in basis. You can learn more about the targets feature on the Ember.js blog.

postcssOptions: {
  compile: {
    enabled: true, // defaults to true
    browsers: ['last 3 versions'], // this will override config found in config/targets.js
    plugins: [
      {
        module: <module>,
        options: {
          ...
        }
      }
    ]
  },
  filter: {
    enabled: true, // defaults to false
    map: false, // defaults to inline, false in production
    browsers: ['last 3 versions'], // this will override config found in config/targets.js
    include: ['styles/*.css'],
    exclude: ['vendor/bootstrap/**/*'],
    plugins: [
      {
        module: <module>,
        options: {
          ...
        }
      }
    ]
  }
}

Example

Install the autoprefixer plug-in:

npm i --save-dev autoprefixer

Specify some plug-ins in your ember-cli-build.js:

const EmberApp = require('ember-cli/lib/broccoli/ember-app');
const autoprefixer = require('autoprefixer');

module.exports = function (defaults) {
  const app = new EmberApp(defaults, {
    postcssOptions: {
      compile: {
        enabled: false,
        browsers: ['last 3 versions'], // this will override config found in config/targets.js
      },
      filter: {
        enabled: true,
        plugins: [
          {
            module: autoprefixer,
            options: {
              browsers: ['last 2 versions'] // this will override the config, but just for this plugin
            }
          }
        ]
      }
    }
  });
  return app.toTree();
};

Developing Addons

If you are a developing an addon and would like to use ember-cli-postcss to process the CSS to automatically be included in the vendor.css of Ember applications consuming the addon, there are 2 steps to follow.

create your styles in addon/styles/addon.css (you can import other CSS files if a postcss import plugin is installed)
configure your addon’s options to process postcss:

// index.js
const CssImport = require('postcss-import')
const CssNext = require('postcss-cssnext')

module.exports = {
  options: {
    postcssOptions: {
      compile: {
        enabled: true,
        plugins: [
          { module: CssImport },
          { module: CssNext }
        ]
      }
    }
  }
  ...
}

Migrating from other Processors

If you’d like to migrate a project from one of the other processors, such as Less, Sass, or Stylus, you can configure Postcss with an appropriate parser and set of plugins that provides an equivalent set of features.

This then allows you to use additional Postcss plugins at the end of the compilation to continue transforming your styles for more powerful control of authoring styles in your application. This also plays nicely with ember-component-css.

So far this migration process has been tested when switching from Sass.

Switching from Sass

One common use case is to transition from using Sass to Postcss or using them both together. As of ember-cli-postcss@3.7.0 this is possible with the right combination of options and plugins.

There are three key pieces of configuration:

Set the parser to postcss-scss
Configure the extension to match your files (ie. 'scss')
Use @csstools/postcss-sass as the first plugin

Your configuration options in ember-cli-build.js would contain the following options for this addon:

  postcssOptions: {
    compile: {
      extension: 'scss',
      enabled: true,
      parser: require('postcss-scss'),
      plugins: [
        {
          module: require('@csstools/postcss-sass'),
          options: {
            includePaths: [
              'node_modules/tachyons-sass',
            ],
          },
        },
        ...
      ],
    },
    ...
  }

This allows your to switch your CSS processing pipeline to use postcss without being hugely disruptive as you can keep the Sass features and .scss or .sass file extension. The importing feature of @csstools/postcss-sass will also look for .css files, so you can choose to gradually rename your files from Sass partials _<filename>.scss to <filename>.css without breaking anything.

If your goal is to completely move away from using Sass features you can remove the parser, remove the sass plugin, use an import plugin that fits your needs and ensure that your files have the .css extension.

Experimental Features

Custom Properties Service

CSS variables are now supported by many major browsers. The values of these variables can be accessed, set, and removed using JavaScript. This addon now exports a service, which provides methods to work with CSS variables. Each method is a wrapper around the browser API, which includes a check for browser support before executing.

The service provides 3 methods:

getVal ({ element = docEl, variableName })
setVal ({ element = docEl, variableName, variableValue })
removeVal ({ element = docEl, variableName })

A Contrived Example:

import { inject } from '@ember/service'

export default <ember object>.extend({
  customProperties: inject(),
  ...

  nightMode() {
    this.get('customProperties').setVal({variableName: '--background', variableValue: 'black'})
    this.get('customProperties').setVal({variableName: '--text', variableValue: 'white'})
  },

  dayMode() {
    this.get('customProperties').setVal({variableName: '--background', variableValue: 'white'})
    this.get('customProperties').setVal({variableName: '--text', variableValue: 'black'})
  },
})

Note: if you are using postcss-custom-properties, ensure you configure the option { preserve: true }

hbrysiewicz/ember-cli-postcss