PostCSS Bidirection 
PostCSS plugin that polyfill Bi-directional CSS proposal from W3C to suppot direction-sensitive rules, a.k.a Left-To-Right (LTR) and Right-To-Left (RTL) in all browsers.
Install
npm install --save-dev postcss-bidirection
Usage
Install postcss-bidirection via npm:
postcss([ require('postcss-bidirection') ])See PostCSS docs for examples for your environment.
To check the layout change, in your HTML file, add attribute in your html tags
<html dir="rtl">
Or, in your js file, set document.dir = 'rtl' or document.dir = 'ltr'.
Examples
PostCSS Bidirection support syntax based on https://wiki.mozilla.org/Gaia/CSS_Guidelines
Text alignment example
Input
.foo {
text-align: start;
}Output
.foo {
text-align: left;
}
html[dir="rtl"] .foo {
text-align: right;
}Padding Example
Input
.foo {
padding-inline-start: 1px;
}Output
.foo {
padding-left: 1px;
}
html[dir="rtl"] .foo {
padding-right: 1px;
}Border Width Example
Input
.foo {
border-inline-start-width: 1px;
}Output
.foo {
border-left-width: 1px;
}
html[dir="rtl"] .foo {
border-right-width: 1px;
}Absolute Positioning Example
Input
.foo {
inset-inline-start: 1px;
}Output
.foo {
left: 1px;
}
html[dir="rtl"] .foo {
right: 1px;
}All supported syntax are listed below
| left/right | begin/end |
|---|---|
| text alignment | |
| text-align: left | text-align: start |
| text-align: right | text-align: end |
| float: left | float: start |
| float: right | float: end |
| clear: left | clear: start |
| clear: right | clear: end |
| padding, margin, border | |
| padding-left | padding-inline-start |
| padding-right | padding-inline-end |
| border-left | border-inline-start |
| border-right | border-inline-end |
| border-left-color | border-inline-end-color |
| border-right-color | border-inline-start-color |
| border-left-style | border-inline-start-style |
| border-right-style | border-inline-end-style |
| border-left-width | border-inline-start-width |
| border-right-width | border-inline-end-width |
| border-top-left-radius | border-top-inline-start-radius |
| border-top-right-radius | border-top-inline-end-radius |
| border-bottom-left-radius | border-bottom-inline-start-radius |
| border-bottom-right-radius | border-bottom-inline-end-radius |
| margin-left | margin-inline-start |
| margin-right | margin-inline-end |
| absolute positioning | |
| left | inset-inline-start |
| right | inset-inline-end |
| left | offset-inline-start (obsolete) |
| right | offset-inline-end (obsolete) |
Options
postcss-bidirection accepts an options object.
const plugin = require('postcss-bidirection');
const opts = {
...
};
postcss([ plugin(opts) ]).process(input) ...
Custom Selectors
By default, postcss-bidirection prefixes generated CSS selectors with html[dir="rtl"] or html[dir="ltr"]. The buildSelector option allows you to override this behavior.
This callback gets called once for every selector of every rule that contains translated properties. If the rule has multiple selectors separated by commas, then it will be called multiple times for that rule.
It takes two arguments:
- the original CSS selector of the rule that we are translating
- The direction to which it is being translated. Can be
rtlorltr.
It should return a CSS selector string, which will be attached to the translated CSS rule.
For example, to drop html from generated selectors, pass a custom buildSelector function to the plugin.
const opts = {
buildSelector = function(selector, direction) {
return '[dir=" + direction + '"] ' + selector;
}
};
let bidirection = require('postcss-bidirection');
postcss([ bidirection(opts) ]);
Input
.foo {
text-align: start;
}Now we have [dir="rtl"] instead of html[dir="rtl"] in the output:
.foo {
text-align: left;
}
[dir="rtl"] .foo {
text-align: right;
}Debugging
Install postcss-debug
npm install -g postcss-debugThen run postcss-debug with command
postcss-debug sample.cssReferences
Firefox OS / B2G OS
These CSS syntax are already in production in Mozilla's Firefox OS, which could be installed as an Android launcher. Once its started, open Settings > Language and choose an sample RTL Language to check the result.