Awesome

bidi-css-js

Logical conversion of flow-relative properties and values for CSS in JS objects

The problem

With properties and value containing a physical direction, e.g., margin-left or float: right, CSS has traditionally been planned and authored to accommodate for a single-direction flow of content - either from left to right, or from right to left. Reality, however, often requires that we author our styles in a manner that can easily be applied independently of the document or component flow-direction.

CSS seems to now slowly starting to progress in the right direction, towards allowing the authoring of flow-realtive styles. Flexbox got this right with justify-content, align-items, etc., and an initial CSSWG proposal to address the issue is in place. The most basic of features, such as text-align: start are already supported in some browsers and others, such as margin-start, have some prefixed support. Most of the proposed features, however, are not currently implemented in any browser support.

This solution

This library aims to provide a way to easily author styles, (mostly) in line with the CSSWG proposal (and expand on it a little bit), while still ensuring backwards compatibility with the way thing were done before.

It is built using the core logic provided by Kent C. Dodds's rtl-css-js, and is basically just a thin layer around it providing different behavior.

It is a function with accepts two arguments: a CSS-in-JS object, and a string indicating the flow-direction according to which the styles object will be parsed.

It will convert, for instance, paddingStart to either paddingLeft or paddingRight, as well as all other properties where it makes sense to do so, depending on the provided flowDirection

Not a polyfill

It is important to note that this package is not a true polyfill for the proposal, as all start and end properties (and so on) are converted to left or right values (etc.), and will not automatically flip when the flow direction of the element, inherited or otherwise is changes in by the html dir attribute or the direction css property.

Four directional shorthand properties

The proposal alters the way values for four-directional shorthand properties (padding, margin, etc.) are written when using the logical keyword.

The values of four-directional shorthand properties, without the logical keyword are written clock-wise: top, right, bottom and left. While in ltr mode, that would translate to block-start, inline-end, block-end and inline-start. However, under the new spec, when the logical keyword is used, values order is interpreted as block-start, inline-start, block-end and inline-end.

Earlier versions of this library got this wrong, and it was corrected in version 2.0.0

Installation

This module is distributed via npm which is bundled with node and should be installed as one of your project's dependencies:

yarn add bidi-css-js
# or
npm install --save bidi-css-js

Usage

This library exposes a CommonJS, as well as an ES Module and UMD with a bidiCSSJS global.

// If using CommonJS
const bidiCSSJS = require('bidi-css-js') 

// If using ES Modules
import bidiCSSJS from 'bidi-css-js/bidi-css-js.esm' 
const styles = bidiCSSJS({paddingStart: 23}, 'rtl')
console.log(styles) // logs {paddingRight: 23}

You can also just include a script tag in your browser and use the bidiCSSJS variable:

<script src="https://unpkg.com/bidi-css-js"></script>
<script>
  const styles = bidiCSSJS({paddingStart: 23}, 'rtl')
  console.log(styles) // logs {paddingRight: 23}
</script>

Logical properties and values

This library is intended to mimic the implementation suggested in the CSSWG's Logical Properties and Values Level 1 proposal, with some minor additional sugar. It only covers the inline-flow (e.g., left<->right) aspects of the proposal and not its block-flow (e.g. top<->bottom) aspects.

Flow-relative properties:

Longhand properties

Shorthand properties

From the spec: The shorthand properties for margin, padding, and border set values for physical properties by default. But authors can specify the logical keyword at the beginning of the property value to indicate that the values map to the flow-relative properties instead of the physical ones. The following [CSS21] shorthand properties [ ... ] accept the logical keyword: margin, padding, border-width, border-style, border-color. [ ... ] When the logical keyword is present in the value, the values that follow are assigned to the flow-relative properties as follows:

• If only one value is set, the value applies to all four flow-relative longhands.
• If two values are set, the first is for block-start and block-end, the second is for inline-start and inline-end.
• If three values are set, the first is for block-start, the second is for inline-start and inline-end, and the third is for block-end.
• If four values are set, they apply to the block-start, inline-start, block-end, and inline-end sides in that order.

Example:

bidiCSSJS({
  margin: 'logical 0 10px 0 20px'
}, 'rtl'); // => { margin: '0 10px 0 20px' }
bidiCSSJS({
  margin: 'logical 0 10px 0 20px'
}, 'ltr'); // => { margin: '0 20px 0 10px' }

For convinience, the library also transforms the following properties in a similar manner, although they are not included in the spec:

Flow-relative values:

In properties that do not accept the logical keword , values containing the following keywords will be automatically transformed. This is not 100% spec complient.

Caveats

Same as rtl-css-js:

This library falls short of a polyfill, and does not accommodate for dynamic changes in the flow direction. See here

While not actually a real caveat, it is worth noting that the proposal changes the way four-directional shorthand properties are evaluated. see here

background

Right now background and backgroundImage just replace all instances of ltr with rtl and right with left. This is so you can have a different image for your LTR and RTL, and in order to flip linear gradients. Note that this is case sensitive! Must be lower case. Note also that it will not change bright to bleft. It's a little smarter than that. But this is definitely something to consider with your URLs.

Thanks

Kent C. Dodds and all other contributors to rtl-css-js. As mentioned above, this library is not much more than a thin wrapper around it's core logic.

Contributors

Thanks goes to these people (emoji key):

This project follows the all-contributors specification. Contributions of any kind welcome!

LICENSE

MIT