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:

1yarn add bidi-css-js
2# or
3npm install --save bidi-css-js

Usage

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

1// If using CommonJS
2const bidiCSSJS = require('bidi-css-js') 
3
4// If using ES Modules
5import bidiCSSJS from 'bidi-css-js/bidi-css-js.esm' 
6const styles = bidiCSSJS({paddingStart: 23}, 'rtl')
7console.log(styles) // logs {paddingRight: 23}

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

1<script src="https://unpkg.com/bidi-css-js"></script>
2<script>
3  const styles = bidiCSSJS({paddingStart: 23}, 'rtl')
4  console.log(styles) // logs {paddingRight: 23}
5</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

Property	LTR Value	RTL Value	Notes
paddingStart	paddingLeft	paddingRight
paddingEnd	paddingRight	paddingLeft
marginStart	marginLeft	marginRight
marginEnd	marginRight	marginLeft
paddingInlineStart	paddingLeft	paddingRight
paddingInlineEnd	paddingRight	paddingLeft
marginInlineStart	marginLeft	marginRight
marginInlineEnd	marginRight	marginLeft
insetInlineStart	left	right
insetInlineEnd	right	left
start	left	right	This property is not part of the official spec and only included for convinience because insetInlineStart is so cumbersome. If you`d like to keep 100% compatibility with the spec, avoid usind this property
end	right	left	This property is not part of the official spec and only included for convinience because insetInlineEnd is so cumbersome. If you`d like to keep 100% compatibility with the spec, avoid usind this property
borderStart	borderLeft	borderRight	--
borderEnd	borderRight	borderLeft	--
borderStartColor	borderLeftColor	borderRightColor	--
borderEndColor	borderRightColor	borderLeftColor	--
borderStartStyle	borderLeftStyle	borderRightStyle	--
borderEndStyle	borderRightStyle	borderLeftStyle	--
borderStartWidth	borderLeftWidth	borderRightWidth	--
borderEndWidth	borderRightWidth	borderLeftWidth	--
borderInlineStart	borderLeft	borderRight	--
borderInlineEnd	borderRight	borderLeft	--
borderInlineStartColor	borderLeftColor	borderRightColor	--
borderInlineEndColor	borderRightColor	borderLeftColor	--
borderInlineStartStyle	borderLeftStyle	borderRightStyle	--
borderInlineEndStyle	borderRightStyle	borderLeftStyle	--
borderInlineStartWidth	borderLeftWidth	borderRightWidth	--
borderInlineEndWidth	borderRightWidth	borderLeftWidth	--
borderTopStartRadius	borderTopLeftRadius	borderTopRightRadius	This property is, at the moment, missing from the spec, but is expected to be defined at a later stage. See w3c/csswg-drafts#491
borderTopEndRadius	borderTopRightRadius	borderTopLeftRadius	This property is, at the moment, missing from the spec, but is expected to be defined at a later stage. See w3c/csswg-drafts#491
borderBottomStartRadius	borderBottomLeftRadius	borderBottomRightRadius	This property is, at the moment, missing from the spec, but is expected to be defined at a later stage. See w3c/csswg-drafts#491
borderBottomEndRadius	borderBottomRightRadius	borderBottomLeftRadius	This property is, at the moment, missing from the spec, but is expected to be defined at a later stage. See w3c/csswg-drafts#491
borderStartStartRadius	borderTopLeftRadius	borderTopRightRadius
borderStartEndRadius	borderTopRightRadius	borderTopLeftRadius	This property is, at the moment, missing from the spec, but is expected to be defined at a later stage. See w3c/csswg-drafts#491
borderEndStartRadius	borderBottomLeftRadius	borderBottomRightRadius	This property is, at the moment, missing from the spec, but is expected to be defined at a later stage. See w3c/csswg-drafts#491
borderEndEndRadius	borderBottomRightRadius	borderBottomLeftRadius	This property is, at the moment, missing from the spec, but is expected to be defined at a later stage. See w3c/csswg-drafts#491

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:

1bidiCSSJS({
2  margin: 'logical 0 10px 0 20px'
3}, 'rtl'); // => { margin: '0 10px 0 20px' }
4bidiCSSJS({
5  margin: 'logical 0 10px 0 20px'
6}, '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:

Property	Example	LTR Value	RTL Value	Notes
backgroundImage	logical url(/foo/bar-ets.png)	url(/foo/bar-rtl.png)	url(/foo/bar-ltr.png)	ets is short for end-to-start; ste is short for start-to-end
backgroundImage	logical linear-gradient(to start top, blue, red)	logical linear-gradient(to left top, blue, red)	logical linear-gradient(to right top, blue, red)
backgroundImage	logical repeating-linear-gradient(to start, #00ff00 0%, #ff0000 100%)	logical repeating-linear-gradient(to left, #00ff00 0%, #ff0000 100%)	logical repeating-linear-gradient(to right, #00ff00 0%, #ff0000 100%)
backgroundPosition	logical start top	left top	right top	--
backgroundPosition	logical 77% 40%	77% 40%	23% 40%	--
backgroundPositionX	See backgroundPosition
background	See backgroundImage and backgroundPosition
borderRadius	logical 1px 2px 3px 4px	1px 2px 3px 4px	2px 1px 4px 3px	Will hopefuly be included at a later stage. See w3c/csswg-drafts#1776
borderRadius	logical 1px 2px 3px 4px / 5px 6px 7px 8px	1px 2px 3px 4px / 5px 6px 7px 8px	2px 1px 4px 3px / 6px 5px 8px 7px	Will hopefuly be included at a later stage. See w3c/csswg-drafts#1776
boxShadow	logical -1px 2px 3px 3px red	-1px 2px 3px 3px red	1px 2px 3px 3px red
boxShadow	logical inset 1px 2px 3px 3px red	inset 1px 2px 3px 3px red	inset -1px 2px 3px 3px red
mozBoxShadow	See boxShadow	--	--	--
webkitBoxShadow	See boxShadow	--	--	--
textShadow	logical red -2px 0	red -2px 0	red 2px 0	--
textShadow	logical -2px 0 red	-2px 0 red	2px 0 red	--
transform	logical translate(30%)	translate(30%)	translate(-30%)	Currently only operates on translate[X]
transform	logical translateX(30%)	translateX(30%)	translateX(-30%)	Currently only operates on translate[X]
transform	logical translate(30%, 20%)	traslate(30%, 20%)	translate(-30%, 20%)	Currently only operates on `translate[X
transform	logical translateY(30px) rotate(20deg) translateX(10px)	translateY(30px) rotate(20deg) translateX(10px)	translateY(30px) rotate(20deg) translateX(-10px)	Currently only operates on `translate[X
transform	logical translate3d(30%, 20%, 10%)	translate3d(30%, 20%, 10%)	translate3d(-30%, 20%, 10%)	Currently only operates on translate[X]
mozTransform	See transform	--	--	--
webkitTransform	See transform	--	--	--
transformOrigin	logical start top	left top	right top	--
transformOrigin	logical 77% 40%	77% 40%	23% 40%	--
mozTransformOrigin	logical start top	left top	right top	--
mozTransformOrigin	logical 77% 40%	77% 40%	23% 40%	--
webkitTransformOrigin	logical start top	left top	right top	--
webkitTransformOrigin	logical 77% 40%	77% 40%	23% 40%	--

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.

Value	LTR Value	RTL Value	Notes
'ste'	'ltr'	'rtl'	Not part of the official spec
'ets'	'rtl'	'ltr'	Not part of the official spec
'inline-start'	'left'	'right'
'inline-end'	'right'	'left'
'start'	'left'	'right'
'end'	'right'	'left'
'start-resize'	'w-resize'	'e-resize'	Not part of the spec
'end-resize'	'e-resize'	'w-resize'	Not part of the spec
'bottomstart-resize'	'sw-resize'	'se-resize'	Not part of the spec
'bottomend-resize'	'se-resize'	'sw-resize'	Not part of the spec
'topstart-resize'	'nw-resize'	'ne-resize'	Not part of the spec
'topend-resize'	'ne-resize'	'nw-resize'	Not part of the spec

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):

Jonathan Pollak 💻 📖 ⚠️

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

LICENSE

MIT