PostCSS Insert

A PostCSS plugin that inserts CSS properties from one class into another, like Sass' @extend only better!

Alright, if you've used Sass before you know about @extend the concept is pretty simple: you take one classes properties and add them to another class in a simple way. In theory, @extend is awesome, but it doesn't work the way you expect. See this to see how Sass handles extend.

Mixins with Sass work better, you create a bunch of properties in a mixin and you just @include them wherever you want. But, you now have this extra thing...the mixin itself, it feels kinda dirty to me. This really should be a solved problem, but it's not for some reason.

What I wanted was a way to have the simplicity of @extend with the behavior of a @mixin.

Funny thing is I wasn't the only one thinking of it. Adam Wathen was thinking about this when he created Tailwinds. Adam created a PostCSS plugin called @apply which did almost everything I wanted it to do...except it was part of a framework. Now, Tailwinds is great, I have no issue with it, but I wanted this without needing a framework. Also, I didn't like the name @apply because that name was being used with custom properties in CSS. I think its been deprecated, but there's a chance it will be taken up again in the future. To me, @apply is a great name, but it comes with some potential baggage that I'd have to deal with later on, also I feel like @insert is more descriptive of what the plugin is doing.

Install

$ npm install postcss-insert`

CSS Usage

Alright, so how do we use this thing? Take a look below:

.bar {
color: green;
}
.foo {
@insert .bar;
}

Output

.bar {
color: green;
}
.foo {
color: green;
}

Obviously this is a pretty contrived example, but you can see what we're doing here. A better example may be extending a button class:

.btn {
padding:5px15px;
text-transform: uppercase;
font-size:18px;
}
.btn-primary {
@insert .btn;
background-color: blue;
}

Output

.btn {
padding:5px15px;
text-transform: uppercase;
font-size:18px;
}
.btn-primary {
padding:5px15px;
text-transform: uppercase;
font-size:18px;
background-color: blue;
}

All props come over, even !important...unless you disable it

By default, @insert will not strip !important, but there's an option stripImportant that you can set to true and it will...well strip the !important:

.bar {
color: green;
font-size:22px!important;
border:1px solid red;
}
.foo {
@insert .bar;
}

Output:

.bar {
color: green;
font-size:22px!important;
border:1px solid red;
}
.foo {
color: green;
font-size:22px!important;
border:1px solid red;
}

With stripImportant: true you'd get the following:

.bar {
color: green;
font-size:22px!important;
border:1px solid red;
}
.foo {
@insert .bar;
}

Output:

.bar {
color: green;
font-size:22px!important;
border:1px solid red;
}
.foo {
color: green;
font-size:22px;
border:1px solid red;
}

This works inside of media queries...unless you disable it

@media (min-width:400px) {
.bar {
color: green;
font-size:22px!important;
border:1px solid red;
}
}
.foo {
@insert .bar;
}

Output:

@media (min-width:400px) {
.bar {
color: green;
font-size:22px!important;
border:1px solid red;
}
}
.foo {
color: green;
font-size:22px!important;
border:1px solid red;
}

General Plugin Usage

postcss([require('postcss-insert')]);

Recommendation

I recommend that this plugin run last in your PostCSS stack. If you're doing any sort of transforms where a class doesn't exist @insert would fail because it can't find the class. If you run this last (or second-to-last right before something like mqpacker) you'll ensure that all classes are there and ready to go. I may eventually add some sort of silent fail option if it can't find a class, but right now that is not the case. Happy coding!

See PostCSS docs for examples for your environment.