j2c

j2c

A tiny CSS in JS solution. 1.1 KiB mingzipped.

Supports local classes by default, mixins, @rules and nested selectors. Composable. Extensible.

This is the "how to" document. For the motivation behind the library, check out the home page.

Table of Contents

• Installation
• Usage
  • For inline decalrations: j2c.inline(declarations)
    • Arrays
      • Overloading properties
      • Mixins
    • Vendor prefixes:
  • For building a style sheet: j2c.sheet(rules)
    • Telling selectors and properties apart
    • Combining multiple selectors
    • At-rules
    • CSS Hacks
    • Mixins redux
• Inserting a stylesheet in a document
• Limitations
• TODO
• License: MIT

---

Installation

$ npm install j2c

then

var j2c = require('j2c')

There are also separate builds for AMD, ES6 and a global window.j2c in the dist directory.

Usage

j2c can be used to either assemble inline declarations or full style sheets with, by default, locally unique class names.

Like SASS LESS and Stylus, j2c supports nested at-rules and selectors, and mixins.

Here's an example of locallized class names (as pioneered AFAIK by JSS):

sheet = j2c.sheet({
  ".title": {
    font_size: "3rem",
    "&:before": {
      color: "#00b",
      content: "'#'"
    }
  },
  ".content": {
    line_height: "1.6em",
    padding: "2rem"
  }
});

Unique class names are generated automatically for title and content:

.content_j2c_fvp6zc2gdj35evhsl73ffzq_0 {
    line-height: 1.6em;
    padding: 2rem;
}

.title_j2c_fvp6zc2gdj35evhsl73ffzq_0 {
    font-size: 3rem;
}

.title_j2c_fvp6zc2gdj35evhsl73ffzq_0:before {
    content: '#';
    color: #888;
}

sheet is now a String object with a title and content properties that hold the unique class names. It can be used like this in your view, either on the server, in the browser of for isomorphic apps (let's say this is part of a React view):

<div>
  <style>{sheet}</style>
  <h3 class="{sheet.title}">Hello</h3>
  <div class="{sheet.content}">Foo bar baz...</div>
</div>

The <style>{sheet}</style> construct works in modernish browsers (ie9+). For older IE, see below.

Animation names are also "localized" by default, font names are left untouched.

For inline decalrations: j2c.inline(declarations)

The j2c function walks down JS objects and builds a property:value; list out of it.

j2c.inline({
  background_color:"red",
  border: {
    top$left: {
      width: "1px",
      color: "white"
    }
  }
})

Outputs, as you could expect (white space added for readability):

background-color: red;
border-top-color: white;
border-top-width: 1px;
border-left-color: white;
border-left-width: 1px;

Underscores are automatically turned into dashes so that property names can be left unquoted in the source.

You can combine (sub)properties who share the same value using $ as a separator. It is useful to specify vendor prefixes. Once again, it allows to leave property names unquoted.

Arrays for property ordering and mixins

The order of iteration over the keys of a js object is undefined. If you want to ensure that properties occur in order (say, border before border-left), use an array:

j2c.inline([
  {border: "solid 1px grey"},
  {border_left: "dashed 3px green"}
])

or

j2c.inline({
  border: [
    "solid 1px grey",
    {left: "dashed 3px green"}
  ]
})

border: solid 1px grey;
border-left: dashed 3px green;

More generally, j2c.inline([foo,bar]) is equivalent to j2c.inline(foo) + j2c.inline(bar).

This enables the following techniques:

Overloading properties

If you want to overload a property by using an array at the value level

j2c.inline({
    border_color: ["#33e", "rgba(64,64,255,0.8)"],
})

becomes

border-color:#33e;
border-color:rgba(64,64,255,0.8);

Alternatively:

j2c.inline([
  { border_color: "#33e"},
  { border_color: "rgba(64,64,255,0.8)"}
])

and

j2c.inline({
    border:[
      {color: "#33e"},
      {color: "rgba(64,64,255,0.8)"}
    ]
})

will give the same result.

Mixins

You can mix in properties by using a function call in an array:

function mixin(color) {
  return {
    border_color: color,
    color: color
  }
}

j2c.inline([
  mixin("red"),
  {
    font_size:"2em"
  }
])

'color:red;
border-color:red;
font-size:2em;'

For building a style sheet: j2c.sheet(rules)

s = j2c.sheet({
    "ul.foo": {
        "@media condition": {
            color: "red"
        },
        // properties for the main ul.my_root_class elements
        font: {
            size: "2em",
            family: "sans-serif"
        },
        // underscores in property names are converted to dashes.
        background_color: "#44f",
        // CamelCase is also automatically handled.
        borderRadius:"2px",

        // sub-selector for children element, notice the mandatory initial space
        // signifying a child element.
        " li": {
            padding:{
                left: "5px",
                top: "10px"
            },
            // convenient $ shortcut.
            border: {left$right: {width: "2px"}}
        }
    }
})

Output (beautified):

ul.foo_j2c_fgdl0s2a5fmle5g56rbuax71_0 li{
  padding-left:5px;
  padding-top:10px;
  border-left-width:2px;
  border-right-width:2px;
}
ul.foo_j2c_fgdl0s2a5fmle5g56rbuax71_0{
  font-size:2em;
  font-family:sans-serif;
  background-color:#44f;
}
@media condition{
  ul.foo_j2c_fgdl0s2a5fmle5g56rbuax71_0{
    color:red;
  }
}

Were s.foo === "foo_j2c_fgdl0s2a5fmle5g56rbuax71_0 "

Selector syntax (telling then and properties apart)

tl;dr: always prefix element selectors with a space.

j2c considers that an object key matching /^[-_0-9A-Za-z$]+$/ is a property, and everything else is a (sub-)selector. Since underscores are converted to dashes, it means that property names can be left unquoted in the source, while (sub-)selectors have to be quoted.

White space in selectors is significant. {".foo": {".bar":{...}}} applies to .foo.bar while

Element selectors like p or body match the property pattern and must thus be preceded by a space.

Selectors are concatenated as is, while properties are concatenated with hyphens. {" ul": {" li": {padding: {left:10}}}} becomes ul li{padding-left:10px;}. {" p":{".foo":{color:"red"}}}, is translated to p.foo:{color:red;}.

The properties at a given selector level are guaganteed to appear in the CSS output before the ones of sub-selectors and before those present in nested @-rules.

Global class and animation names.

You can define or refer to global names using the @global{} pseudo at-rule, and the :global() function. This will thus preserve the .foo, .bar and baz names:

s = j2c.sheet({
    "@global": {
        "ul.foo": {
            font_size: "2em",
        }
    }
    "p:global(.bar)" :{
        color:"#f00"
        animation_name: ":global(baz)"
    },
    "@keyframes :global(baz)": {
        // define the global "baz" animation here.
    }
})

@global blocks also globalize animation names (not shown above).

Combining multiple selectors

TODO: refactor this section to mention the SASS-like & placeholder (at any arbitrary position).

Here's a excerpt from the j2c port of the PocketGrid.

j2c.sheet({"@global": {
  ".block,.blockgroup":{
    ",:before,:after":{          // Notice the initial coma.
      box_sizing:"border-box"
    }
  }
}})

Nesting ",:before,:after" inside the ".block,.blockgroup" block combines [".block", ".blockgroup"] with ["", ":before", ":after"], giving

.block,.block:before,.block:after,.blockgroup,.blockgroup:before,.blockgroup:after{
    box-sizing:border-box;
}

Mathy folks call this as a Cartesian product.

At-rules

j2c handles @-rules out of the box, including nested ones.

j2c.sheet({
  "@media screen": {
    " p": {
      foo:"bar",
      "@media (orientation: landscape)": {
        baz:"qux"
      }
    }
  }
})

becomes

@media screen {
  p {
    foo: bar;
  }
  @media (orientation: landscape) {
    p {
      baz: qux;
    }
  }
}

For @keyframes rules, a @-webkit-keyframes block is automatically created with auto-prefixed property names.

At-rules are guarateed to be inserted after the properties and sub-selectors at a given level. This prevents nested @media blocks to be overridden by declarations found out of them.

If you need several media queries where the order of definition is important, or if you need at-rules that must be inserted at the top of a sheet, use arrays.

j2c.sheet([
  {"@import": "url(foo.css)"},
  {"@namespace": "url(http://www.w3.org/1999/xhtml)"},
  {"@namespace": "svg url(http://www.w3.org/2000/svg)"},
  {
    ".your": {sheet:"here"}
  }
])

#### CSS Hacks

Since `sheet.add` only accepts property names that match `/^[-_0-9A-Za-z$]+$/`, it is not possible to express CSS hacks using objects. You can, however, work around the issue by using arrays and strings instead.

Here's another modified excerpt from the PocketGrid port:

```JavaScript
j2c.sheet({
  ".blockgroup": [
    "*zoom: 1; /* hackety hackery */",
    {
      "list-style-type":"none",
      padding:0,
      margin:0
    }
  ]
})

Array elements are inserted in sequence, and string literals are treated as a list of properties, and inserted as is.

Result:

.blockgroup{
*zoom: 1; /* hack */
}
.blockgroup{
  list-style-type:none;
  padding:0;
  margin:0;
}

You can also pass th result of j2c.inline which is less picky about property names.

Mixins redux

Arrays works the same way at the selector level as they do at the property/value one. You can therefore use the method described in the "inline" section.

Vendor prefixes:

Prefixing property names

j2c.inline() , j2c.sheet() and j2c.scoped() take a vendor prefix list as a second, optional argument. When it is present, prefixes are automatically prepended to all properties.

Most of the resulting combinations don't make any sense (-moz-color FTW), and they are simply ignored by browsers. That's the price to pay for the small code size.

j2c.inline({transition:"all 1s"}, ["moz", "webkit"])

-moz-transition:all 1s;
-webkit-transition:all 1s;
transition:all 1s;

Alternatively, you can specify the prefixes by hand using the "$" operator where needed:

j2c.inline({
  // Notice the trailing dollar, required for the unprefixed property.
  _o$_ms$_moz$_webkit$: {foo: "bar"},
  hello: "world"
});

Compiles to

p {
  -o-foo:bar;
  -ms-foo:bar;
  -moz-foo:bar;
  -webkit-foo:bar;
  foo:bar;
  hello:world;
}

Prefixing values

To prefix values, you can use j2c.prefix:

j2c.inline({
  background_image:j2c.prefix(
    "linear-gradient(90deg, #f00, #ff0)",
    ['moz','webkit']
  )
})

background-image: -moz-linear-gradient(90deg, #f00, #ff0);
background-image: -webkit-linear-gradient(90deg, #f00, #ff0);
background-image: linear-gradient(90deg, #f00, #ff0);

There's no support for prefixing a list multiple values (e.g. "linear-gradient(90deg, #f00, #ff0),linear-gradient(90deg, #f00, #ff0)").

@-webkit-keyframes

@keyframes blocks automatically produce their @-webkit-keyframes counterparts, even in the absence of a vendor list argument.

Inserting the stylesheet in the document

Foreword: Please note that the following is based on research on the Web, but not effectively tested in Internet explorer at the moment.

ie9+

Add a text node to a new style element.

var style = document.createElement('style');
style.type = 'text/css'; // my not even be needed
style.appendChild(document.createTextNode(sheet));

In frameworks:

<style>{sheet}</style>

Sweet, innit?

ie8+ (sheets up to 32k in ie8)

As above, but with a link element and a data URI.

<link rel="stylesheet" itemprop="stylesheet" href="{'data:,' + encodeURIComponent(sheet)}" />

Note that ie8 has a 32k limit on the length of data URIs. It supports base 64 in data URIs, but doesn't provide btoa, which would not be useful in this context anyway, since base 64 encoded sheets are larger than URI encoded ones.

ie6+ (unlimited sheet size)

function stylize(element, sheet){
    element.type = 'text/css';
    if (element.styleSheet){
      element.styleSheet.cssText = sheet;
    } else {
      element.appendChild(document.createTextNode(sheet));
    }
    return element;
}
var style = document.createElement('style')
stylize(style);
document.head.appendChild(style);

For this to work in client-side frameworks, you need to grab a handle on the actual <style> DOM node. This means that you must create a custom component/directive.

Here are a few examples:

React:

var j2cComponent = {
   render: function(){
        return <style />
    }
    componentDidMount: function(){
        stylize(React.findDOMNode(this), this.prop.sheet)
    }
}

Mithril:

var j2cComponent = {
    view: function(ctrl, args) {
        return m("style", {
            sheet: args.sheet
            config: function(el, isinit, vdom) {
                if(!isinit) {
                    stylize(el, vdom.attrs.sheet);
                }
            }
        })
    }
}

Angular v1.3- (1.4 is ie9+)

module.directive('j2cSheet', function() {
  return {
    restrict: 'A',
    link: function link(scope, element, attrs) {
        if (element.tagName.toUpperCase() !== "STYLE") throw 'j2cSheet expects a <style> element';
        stylize(element[0], attrs.j2cSheet);
    }
  };
});

module.directive('j2cInline', function() {
  return {
    restrict: 'A',
    link: function link(scope, element, attrs) {
        element[0].style += j2c.inline(attrs.j2cInline);
    }
  };
});

Limitations

Selectors and properties order

j2c relies on JS objects to define selectors and properties. As a consequence, the source order cannot be guaranteed to be respected in the output.

j2c.sheet({
  ".hello": {
    foo:"bar",
    baz:"qux"
  }
})

This may produce either .hello{foo:bar;baz:qux;} or .hello{baz:qux;foo:bar;}.

If you need some selectors or properties to happen in order, use an array of objects.

j2c.sheet({
  ".hello":[
    {foo:"bar"},
    {baz:"qux"}
  ]
})

This will always yield .hello{foo:bar;}.hello{baz:qux;}.

No input validation

j2c knows the bare minimum to output a valid stylesheet when provided with valid input. It will hapily accept invalid selectors, properties and values, and could in that case produce a broken stylesheet.

I may get around and write a validator companion, but I'm not there yet :-).

Little pretty printing

j2c puts each selector list and properties on their own lines, but doesn't indent or add other white space.

For debugging purposes, I recommend that you pipe j2c's output through a [be au ti fier] of your choice.

@keyframes names are global, even in a scoped stylesheet.

It's up to you to pick distinctive names. This is high on the TODO list.

Vendor prefixes corner cases

j2c doesn't provide any facility to auto-prefix a list of values. It is relevant in the context of multiple gradient backgrounds and transition/transition-property values.

TODO:

• Improve the web site. Move the docs there.
• Test DOM insertion methods in old IE.
• Add scoped animation names and maybe font names too?

License: MIT