postcss-styled-syntax

PostCSS syntax for template literals CSS-in-JS (e. g. styled-components, Emotion). It was built to be used as Stylelint custom syntax or with PostCSS plugins.

Syntax supports:

• Full spectrum of styled-components syntax
• Deeply nested interpolations
• Interpolations in selectors, property names, and values
• JavaScript and TypeScript (including files with JSX)
• All functions:
  • styled.foo
  • styled(Component)
  • styled.foo.attrs({})
  • styled(Component).attrs({})
  • css
  • createGlobalStyle

let Component = styled.p`
	color: #bada55;
`;

Install

npm install --save-dev postcss-styled-syntax

Usage

Stylelint

Install syntax and add to a Stylelint config:

{
	"customSyntax": "postcss-styled-syntax"
}

Stylelint custom syntax documentation.

PostCSS

Install syntax and add to a PostCSS config:

module.exports = {
	syntax: 'postcss-styled-syntax',
	plugins: [ /* ... */ ],
};

An example assumes using PostCSS CLI or another PostCSS runner with config support.

How it works

Parsing

Syntax parser JavaScript/TypeScript code and find all supported components and functions (e.g., css``). Then, it goes over them and builds a PostCSS AST, where all found components become Root nodes inside the Document node.

All interpolations within the found component CSS end up in the AST. E. g. for a declaration color: ${brand} Decl node will look like this:

Decl {
	prop: 'color',
	value: '${brand}',
}

When interpolation is not part of any node, it goes to the next node's raws.before. For example, for the following code:

let Component = styled.p`
	${textStyles}

	color: red;
`;

AST will look like:

Decl {
	prop: 'color',
	value: 'red',
	raws: {
		before: '\n\t${textStyles}\n\n\t',
		// ...
	}
}

If there is no next node after interpolation, it will go to parents raws.after. For example, for the following code:

let Component = styled.p`
	color: red;

	${textStyles}
`;

AST will look like:

Root {
	nodes: [
		Decl {
			prop: 'color',
			value: 'red',
		},
	],
	raws: {
		after: '\n\n\t${textStyles}\n'
		// ...
	},
}

Stringifying

Mostly, it works just as the default PostCSS stringifyer. The main difference is the css helper in interpolations within a styled component code. E. g. situations like this:

let Component = styled.p`
	${(props) =>
		props.isPrimary
			? css`
					background: green;
			  `
			: css`
					border: 1px solid blue;
			  `}

	color: red;
`;

css helper inside an interpolation within Component code.

During parsing, the whole interpolation (${(props) ... }) is added as raws.before to color: red node. And it should not be modified. Each css helper remembers their original content (as a string).

When stringifyer reaches a node's raws.before, it checks if it has interpolations with css helpers. If yes, it searches for the original content of css helper and replaces it with a stringified css helper. This way, changes to the AST of the css helper will be stringified.

Known issues

• Double-slash comments (//) will result in a parsing error. Use standard CSS comments instead (/* */). It is definitely possible to add support for double-slash comments, but let's use standard CSS as much as possible

• Source maps won't work or cannot be trusted. I did not disable them on purpose. But did not test them at all. Because of the way we need to handle css helpers within a styled component, source.end positions on a node might change if css AST changes. See the “How it works” section on stringifying for more info.

Acknowledgements

PostCSS for tokenizer, parser, stringifier, and tests for them.

Prettier for styled-components detection function in an ESTree AST.