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Building a PostCSS workflow (part 2)


In the last post, we built a basic PostCSS workflow using Gulp. This post will cover additional features that are nice to have in a workflow but are not required to run it.

We will also look in some detail at postcss-preset-env, what it would allow us to do and how it would work.

The plugins (thoughts) #

The list of plugins that I want to use shows what they are, what I expect them to do, and a little research on SASS equivalency.

postcss-color-function provides color manipulation functions equivalent to SASS @lighten and @darken.
The color functions in this plugin were removed from the CSS Color Module level 5 spec so they are not available in browsers at all, at least not directly.

According to Adam Argyle, one of the CSS Color Module Level 5 spec editors, tweet "no replacements planned, rather succession via relative color syntax. they had too much overlap, so 1 was removed"

See the following Codepen for a demo of the color-mix() function

See this Codepen for a demo of relative color syntax and the color-contrast() function (this demo only work in Safari Technical Preview 125 and later)

Conditional logic
postcss-conditionals offers an if/else statement equivalent to SASS @if
postcss-for allow writing conditional logic in a way that mostly mirror SASS.
postcss-each gives you the ability to loop over an array of values and act on each one
This plugin will treat warnings as errors causing the termination of the script.
This is useful when you want to make sure that you actually fix any warnings or errors in your CSS. However, gulp-sass seems to terminate the script on errors and warnings regardless, so this may be less of an issue
postcss-simple-vars allows us to use SASS variables (beginning with $) in our CSS.
Even though it was implemented in the initial version of the Gulpfile, I'm documenting it here because I'm not sure if this is something I want to use over CSS native custom properties
postcss-define-property allows us to use CSS Custom Properties as defined in CSS Properties and Values API Level 1, a Houdini specification.
The definitions of these properties are more complete since they allow you to define the syntax of the property, a default value, and whether it inherits or not. The downside is that @property is only supported on Chromium browsers so you will likely have to define multiple versions of a given property, likely using @support to target different browsers (chromium browsers and everyone else).

The order of the plugins you use matters. See the plugin's compatibility wiki for more information.

postcss-at-rules-variables allows us to use variables in the @media and @supports at-rules.
I've chosen not to implement this yet as I'm not certain this is not taken care of by other plugins.
This is the PostCSS equivalent to Babel for Javascript. The idea is that it will allow us to use a set of new CSS features at different levels of maturity in the CSS specification process.
The problem is that the list is likely to change over time and it doesn't account for properties that have been removed from the corresponding specification.

Adding the plugins to the workflow #

Because we've already created the Gulpfile the process is simpler when adding additional functionality is a two-step process instead of three steps that we discussed in the previous post.

  1. Install the plugins and require them at the top of the gulpfile
  2. Add the plugins to the processor constant

The additional properties look like this:

const property = require(`postcss-define-property`);
const condition = require('postcss-conditionals');
const each = require('postcss-each');
const pcfor = require('postcss-for');
const colors = require('postcss-color-function');

The full list of processors, including the new ones, is as follows:

const processors = [
    glob: true
    order: [
    'properties-order': 'alphabetical',
    'unspecified-properties-position': 'bottom',

The final test is to actually use the styles in selectors that use the functions and rules.

Edit on Github