postcss-custom-properties-fallback
v1.0.2
Published
Adds fallbacks to your CSS var() functions
Downloads
18,439
Maintainers
Readme
PostCSS Custom Properties Fallback
This plugins adds fallbacks to your CSS Custom Properties and works well as a compantion to PostCSS Custom Properties.
Pop Quiz!
If we remove --color
from :root
, what color will h1
have in modern browsers?
:root {
- --color: red;
}
body {
color: green;
}
h1 {
color: red;
color: var(--color);
}
Red or green, expand the right answer (no cheating/googling!):
Nope, it's green
!
Intuitively it's easy to think that if --color
isn't defined, then the browser should skip the color: var(--color)
and use the valid color: red
above it.
Especially since this is what happens in older browsers that don't support CSS Custom Properties.
The right answer is to use the second argument in var()
(see Example 10 in the spec), also known as the fallback argument:
color: var(--color, red);
Now it works like expected. See the spec for more information on how invalid/missing values are treated.
Right answer! Check the wrong answer to learn why that is.
Usage
Add PostCSS Custom Properties Fallback to your project:
npm install postcss-custom-properties-fallback --save-dev
Use it as a PostCSS plugin:
const postcss = require('postcss');
const postcssCustomPropertiesFallback = require('postcss-custom-properties-fallback');
postcss([postcssCustomPropertiesFallback(/* pluginOptions */)]).process(
YOUR_CSS /*, processOptions */
);
Options
importFrom
The importFrom
option is required. It works like from CSS Custom Properties, except it doesn't support importing from CSS yet.
postcssCustomPropertiesFallback({
importFrom: { customProperties: { '--color': 'red' } },
});
h1 {
color: var(--color);
}
/* becomes */
h1 {
color: var(--color, red);
}