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About
Features
Use cases
Status
Related packages
Installation
Dependencies
Usage examples
API
Authors
License

About

CSS from nested JS data structures. This is a support package for @thi.ng/hiccup.

Following a similar pattern as the @thi.ng/hiccup package, this library generates CSS from plain nested arrays / data structures, functions, iterators.

Features

Uses JS arrays to define selector scopes
Uses JS object to define selector properties
- Multiple objects per scope are combined automatically
Supports nested selectors and computes their cartesian products
Optional CSS class scoping
DOM stylesheet injection
Configurable auto-prefixed properties & vendor prefixes (disabled by default)
Automatically consumes embedded iterators
Supports embedded functions, either:
- to define entire selector branches/scopes
- to produce single selector items
- to produce property values
Quoted functions to support CSS-as-JSON definitions
Various @-rule function wrappers:
- @import
- @keyframes
- @media (incl. nested media queries)
- @namespace
- @supports
Attribute selector functions
Unit formatting wrappers (no conversions yet)
Customizable formatting (2 defaults for compact & pretty printing)

Use cases

Same as LESS / SASS etc., but enables full use of ES6 to define style rules
CSS framework & theme generators
Dynamic CSS generation for components

The overall approach of using S-expressions was inspired by these Clojure projects:

hiccup
garden

Status

STABLE - used in production

Search or submit any issues for this package

Related packages

@thi.ng/hiccup-html - 100+ type-checked HTML5 element functions for @thi.ng/hiccup related infrastructure
@thi.ng/hiccup-svg - SVG element functions for @thi.ng/hiccup & related tooling

Installation

yarn add @thi.ng/hiccup-css

ESM import:

import * as css from "@thi.ng/hiccup-css";

Browser ESM import:

<script type="module" src="https://esm.run/@thi.ng/hiccup-css"></script>

JSDelivr documentation

Package sizes (brotli'd, pre-treeshake): ESM: 2.24 KB

Dependencies

@thi.ng/api
@thi.ng/checks
@thi.ng/errors
@thi.ng/transducers

Note: @thi.ng/api is in most cases a type-only import (not used at runtime)

Usage examples

Three projects in this repo's /examples directory are using this package:

Description	Live demo	Source
hdom update performance benchmark w/ config options	Demo	Source
Generating pure CSS image transitions	Demo	Source
Scroll-based, reactive, multi-param CSS animation basics	Demo	Source

API

Generated API docs

import * as css from "@thi.ng/hiccup-css";

css()

Signature: css(rules: any, opts?: CSSOpts): string

This is the main function exposed by this module. It accepts a JS data structure (array, object, iterator or function) and returns a CSS string. The optional opts arg is used to control formatting, auto-prefixing and other conversion options. See api.ts for reference.

By default the generated CSS uses the css.COMPACT format, causing "minimized" outputs. Pretty printing is supported via the css.PRETTY format preset, see examples further below.

Property formatting only

This feature is only intended for setting an element's .style attrib:

import { css, percent, px } from "@thi.ng/hiccup-css";

css({
    position: "absolute",
    border: 0,
    // function is evaluated during serialization
    top: () => percent((Math.random() * 100) | 0),
    // the entire properties object is passed to functions
    left: (props) => px(props.border),
    // arrays are joined with `,`
    // nested arrays are joined w/ ` `
    font: [["72px", "ComicSans"], "sans-serif"]
});

// "position:absolute;border:0;top:23%;left:0px;font:72px ComicSans,sans-serif;"

Basic selectors

import { css, rem, PRETTY } from "@thi.ng/hiccup-css";

css(
    [
        ["html", "body", { margin: 0, padding: 0 }],
        ["div", { "max-width": rem(30)}],
        ["div.title", { color: "red" }]
    ],
    { format: PRETTY }
);

html, body {
    margin: 0;
    padding: 0;
}

div {
    max-width: 30rem;
}

div.title {
    color: red;
}

Property object merging & re-use

import { css, PRETTY } from "@thi.ng/hiccup-css";

// re-usable property snippets
const border = { border: "1px solid black" };
const red = { color: "red" };

css(
    [
        ["#foo", { background: "white" }, border, red],
        ["#bar", { background: "yellow", color: "black" }, border]
    ],
    { format: PRETTY }
);

#foo {
    background: white;
    border: 1px solid black;
    color: red;
}

#bar {
    background: yellow;
    color: black;
    border: 1px solid black;
}

Iterators & CSS class scoping

import * as tx from "@thi.ng/transducers";

// single rule generator
// e.g. `[".w25", { width: "25%" }]`
const prop = (id, key) => (x) => [id + x, {[key]: css.percent(x)}];

css.css(
    // define iterator to produce a number of width & height css classes
    // `juxt` is used to process given percentage values in parallel and produces a tuple
    // `mapcat` is used to dissolve the tuple and produce a flat stream of generated rules
    // REMEMBER: iterators are lazy and can only be consumed once (not a problem here)
    tx.iterator(
        tx.mapcat(tx.juxt(prop(".w", "width"), prop(".h", "height"))),
        tx.range(25, 101, 25)
    ),
    // supply a scope ID (suffix) for all class names
    { format: css.PRETTY, scope: "_xyz" }
);

.w25_xyz {
    width: 25%;
}

.h25_xyz {
    height: 25%;
}

.w50_xyz {
    width: 50%;
}

.h50_xyz {
    height: 50%;
}

.w75_xyz {
    width: 75%;
}

.h75_xyz {
    height: 75%;
}

.w100_xyz {
    width: 100%;
}

.h100_xyz {
    height: 100%;
}

Nested selectors

Selector nesting can be easily done via array nesting. Each new nesting level defines a child scope of the current selector. The actual CSS selectors are computed using the cartesian product of any selectors in the current scope and their previously defined parents:

import { css, rem, withAttrib, PRETTY } from "@thi.ng/hiccup-css";

css(
    ["header", "footer", { "font-size": rem(1.25) },
        ["nav", { background: "#000", color: "#666" },
            ["ul", { "list-style": "none" }],
            ["li", { padding: rem(0.5) },
                [withAttrib("selected"), { color: "#0cf" }]]]],
    { format: PRETTY }
)

header nav ul, footer nav ul {
    list-style: none;
}

header nav li[selected], footer nav li[selected] {
    color: #0cf;
}

header nav li, footer nav li {
    padding: 0.5rem;
}

header nav, footer nav {
    background: #000;
    color: #666;
}

header, footer {
    font-size: 1.25rem;
}

Parent selector

Child selectors can use the special & prefix to refer to their direct parent to form derived selectors, for example:

import { css, PRETTY } from "@thi.ng/hiccup-css";

css(
    ["#test", { color: "white" },
        ["&.alt", { color: "black" }],
        ["&-alt-bg", { background: "black" }]],
    { format: css.PRETTY }
);

#test.alt {
    color: black;
}

#test-alt-bg {
    background: black;
}

#test {
    color: white;
}

The &-prefixed selectors only refer to their immediate parent, but otherwise behave like all other nested selectors:

import { css, PRETTY } from "@thi.ng/hiccup-css";

css(
    ["outer1", "outer2",
        [".inner1", ".inner2", { color: "red" },
            ["&--green", { color: "green" }],
            ["&--blue", { color: "blue" }]]],
    { format: css.PRETTY }
);

outer1 .inner1--green, outer1 .inner2--green,
outer2 .inner1--green, outer2 .inner2--green {
    color: green;
}

outer1 .inner1--blue, outer1 .inner2--blue,
outer2 .inner1--blue, outer2 .inner2--blue {
    color: blue;
}

outer1 .inner1, outer1 .inner2,
outer2 .inner1, outer2 .inner2 {
    color: red;
}

Pseudo-classes

Pseudo-classes follow the same pattern as other nested selectors shown above:

import { css, PRETTY } from "@thi.ng/hiccup-css";

css(
    ["p", ["a", [":link", {color: "red"}], [":visited", {border: 0}]]],
    { format: PRETTY }
);

p a:link {
    color:red;
}

p a:visited {
    border: 0;
}

Attribute selectors

hiccup-css selector function	CSS
`withAttrib(id)`	`[id]`
`attribEq(id, x, caseSensitve?)`	`[id=x]`
`attribContains(id, x, caseSensitve?)`	`[id~=x]`
`attribPrefix(id, x, caseSensitve?)`	`[id^=x]`
`attribSuffix(id, x, caseSensitve?)`	`[id$=x]`
`attribMatches(id, x, caseSensitve?)`	`[id*=x]`

Auto-prefixed properties

(Currently, only prefixed properties are supported. Auto-prefixing based on property values is planned, but currently low priority.)

import { css, PRETTY } from "@thi.ng/hiccup-css";

css(
    ["div", {"border-radius": "4px"}],
    { autoprefix: ["border-radius"], format: PRETTY }
);

div {
    -moz-border-radius: 4px;
    -ms-border-radius: 4px;
    -o-border-radius: 4px;
    -webkit-border-radius: 4px;
    border-radius: 4px;
}

Media queries

Media queries (optionally nested) are supported via the at_media() and at_supports() functions, both taking an object (or string) of conditionals and a body which will be based to css().

The key-value pairs of the conditional object are interpreted as follows and ALWAYS combined using and:

Key/Value pair	Result
`"min-width": "10rem"`	`(min-width: 10rem)`
`print: true`	`print`
`print: false`	`(not print)`
`print: "only"`	`only print`

Note: In CSS Level 3, the not operator can't be used to negate an individual media feature expression, only an entire media query.

import { css, at_media, percent, rem, PRETTY } from "@thi.ng/hiccup-css";

css(
    at_media(
        { screen: true, "min-width": rem(10) },
        [
            [".col", { width: percent(50)}],
            [
                at_media(
                    { "min-width": "20rem" },
                    [".col", { padding: rem(1) }]
                )
            ]
        ]
    ),
    { format: PRETTY }
);

@media screen and (min-width:10rem) {

    .col {
        width: 50%;
    }

    @media (min-width:20rem) {

        .col {
            padding: 1rem;
        }

    }

}

Keyframes

import { css, at_keyframes, PRETTY } from "@thi.ng/hiccup-css";

css(
    at_keyframes("fadein", { opacity: 0 }, { opacity: 1 }),
    { format: PRETTY }
);

@keyframes fadein {

    0% {
        opacity: 0;
    }

    100% {
        opacity: 1;
    }

}

import { css, at_keyframes, PRETTY } from "@thi.ng/hiccup-css";

css(
    at_keyframes(
        "rgbfade",
        {
            0: {
                color: "red"
            },
            50: {
                color: "green"
            },
            100: {
                color: "blue"
            }
        }
    ),
    { format: PRETTY }
);

@keyframes rgbfade {

    0% {
        color: red;
    }

    50% {
        color: green;
    }

    100% {
        color: blue;
    }

}

Animations

Animations can be defined via the animation() function and define new @keyframes with given id and related class of same name to configure given animation opts. Only the durationoption is given a default value (250ms), all others are optional.

import { css, animation } from "@thi.ng/hiccup-css";

css(
    animation(
        "delayed-fade-in",
        { delay: "0.5s" },
        { opacity: 0 },
        { opacity: 1 }
    )
);

Results in:

@keyframes delayed-fade-in {
    0% {
        opacity: 0;
    }
    100% {
        opacity: 1;
    }
}

.delayed-fade-in {
    animation-duration: 250ms;
    animation-name: delayed-fade-in;
    animation-delay: 0.5s;
}

DOM stylesheet injection

CSS strings can be installed into the DOM <head> element via injectStyleSheet():

import { css, injectStyleSheet } from "@thi.ng/hiccup-css";

injectStyleSheet(
    css([
        "body", { background: "#000", color: "#fff" }
    ])
);

General function handling

Functions are handled differently based on their position in the rule tree. Also see the section on Quoted functions below...

Functions in scope head position

If a function is given as arg to css() or is in the head position (first element) of a rule scope, the function is expected to produce output directly and is called with an empty result accumulator array and the CSSOpts object passed to css(). This form is mainly used by the various at_*() functions provided (e.g. at_media() example above).

import { css, at_import } from "@thi.ng/hiccup-css";

css(at_import("foo.css", "screen"));
// "@import url(foo.css) screen;"

The following example illustrates the head position placement, using the comment() function to emit CSS comments.

import { css, comment } from "@thi.ng/hiccup-css";

css([
    // comments are usually omitted with the default format (css.COMPACT)
    // pass `true` as 2nd arg to force inclusion
    comment("generated, please don't edit", true),
    ["div", { margin: 0 }]
]);
// "/*generated, don't edit*/div{margin:0;}"

Functions in other positions

If a function is located anywhere else in a rule scope array (2nd index or later), it will be called without arguments and the return value used in its place. Any returned functions will be eval'd recursively in the same manner.

Quoted functions

One of this project's use cases is to support stylesheets defined as JSON. Since functions cannot be used there, an optional mechanism to map strings to functions is provided:

["function-name", ...args]

The quoted function name is looked up in a dictionary and if found, called with all remaining elements in the same array. I.e. ["@import", "foo.css"] will be the same result as at_import("foo.css").

IMPORTANT: Quoted functions are only supported in the head position of a scope.

import * as css from "@thi.ng/hiccup-css";

const styles = [
    ["@comment", " CSS from JSON"],
    ["@import", "print.css", "print"],
    ["@media",
        { "screen": true, "min-width": "10em" },
        ["div", { "font-size": "80%" }]
    ],
    ["@keyframes", "fadein", { "opacity": 0}, { "opacity": 1 }]
];

css.css(styles, { format: css.PRETTY, fns: css.QUOTED_FNS });

// btw. QUOTED_FNS is simply:
const QUOTED_FNS = {
    "@comment": css.comment,
    "@import": css.at_import,
    "@keyframes": css.at_keyframes,
    "@media": css.at_media,
    "@namespace": css.at_namespace,
    "@supports": css.at_supports,
}

/*
    CSS from JSON
 */
@import url(print.css) print;
@media screen and (min-width:10em) {

    div {
        font-size: 80%;
    }

}

@keyframes fadein {

    0% {
        opacity: 0;
    }

    100% {
        opacity: 1;
    }

}

Authors

Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-hiccup-css,
  title = "@thi.ng/hiccup-css",
  author = "Karsten Schmidt",
  note = "https://thi.ng/hiccup-css",
  year = 2016
}

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README.md

README.md

About

Features

Use cases

Status

Related packages

Installation

Dependencies

Usage examples

API

css()

Property formatting only

Basic selectors

Property object merging & re-use

Iterators & CSS class scoping

Nested selectors

Parent selector

Pseudo-classes

Attribute selectors

Auto-prefixed properties

Media queries

Keyframes

Animations

DOM stylesheet injection

General function handling

Functions in scope head position

Functions in other positions

Quoted functions

Authors

License

Files

README.md

Latest commit

History

README.md

File metadata and controls

About

Features

Use cases

Status

Related packages

Installation

Dependencies

Usage examples

API

css()

Property formatting only

Basic selectors

Property object merging & re-use

Iterators & CSS class scoping

Nested selectors

Parent selector

Pseudo-classes

Attribute selectors

Auto-prefixed properties

Media queries

Keyframes

Animations

DOM stylesheet injection

General function handling

Functions in scope head position

Functions in other positions

Quoted functions

Authors

License