style-mod

Minimal CSS module shim for generating CSS rules and anonymous class names for sets of style declarations and attaching such a set to a document or shadow root.

Using it would look something like this:

const {StyleModule} = require("style-mod")
const myModule = new StyleModule({
  main: {
    fontFamily: "Georgia, 'Nimbus Roman No9 L'",
    margin: "0"
  },
  callout: {
    color: "red",
    fontWeight: "bold",
    "&:hover": {color: "orange"}
  }
})
StyleModule.mount(document, myModule)
document.body.className = myModule.main

This code is open source, released under an MIT license.

Documentation

class StyleModule

Style modules encapsulate a set of CSS rules defined from JavaScript. Their definitions are only available in a given DOM root after it has been mounted there with StyleModule.mount.

Style modules should be created once and stored somewhere, as opposed to re-creating them every time you need them. The amount of CSS rules generated for a given DOM root is bounded by the amount of style modules that were used. So to avoid leaking rules, don't create these dynamically, but treat them as one-time allocations.

• new StyleModule(spec: Object< Style >, options: ?{finish: ?fn(string) → string})
  Create a style module from the given spec.

  When finish is given, it is called on regular (non-@) selectors (after & expansion) to compute the final selector.

• getRules() → string
  Returns a string containing the module's CSS rules.

• static newName() → string
  Generate a new unique CSS class name.

• static mount(root: Document | ShadowRoot, modules: [StyleModule] | StyleModule)
  Mount the given set of modules in the given DOM root, which ensures that the CSS rules defined by the module are available in that context.

  Rules are only added to the document once per root.

  Rule order will follow the order of the modules, so that rules from modules later in the array take precedence of those from earlier modules. If you call this function multiple times for the same root in a way that changes the order of already mounted modules, the old order will be changed.

Where the Style type is defined as:

• Style: Object< Style | string >
  A style is an object that, in the simple case, maps CSS property names to strings holding their values, as in {color: "red", fontWeight: "bold"}. The property names can be given in camel-case—the library will insert a dash before capital letters when converting them to CSS.

  If you include an underscore in a property name, it and everything after it will be removed from the output, which can be useful when providing a property multiple times, for browser compatibility reasons.

  A property in a style object can also be a sub-selector, which extends the current context to add a pseudo-selector or a child selector. Such a property should contain a & character, which will be replaced by the current selector. For example {"&:before": {content: '"hi"'}}. Sub-selectors and regular properties can freely be mixed in a given object. Any property containing a & is assumed to be a sub-selector.

  Finally, a property can specify an @-block to be wrapped around the styles defined inside the object that's the property's value. For example to create a media query you can do {"@media screen and (min-width: 400px)": {...}}.