Adds fallbacks to your CSS var() functions
MIT License
This plugins adds fallbacks to your CSS Custom Properties and works well as a compantion to PostCSS Custom Properties.
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);
}
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.
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 */
);
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);
}