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PostCSS Bidirection Build Status Npm version

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 rtl or ltr.

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-debug

Then run postcss-debug with command

postcss-debug sample.css

References

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.