postcss-multi-value-display

PostCSS plugin to transform CSS Display Module Level 3 multi-value syntax into legacy single-value equivalents (when available).

Example

const fs = require("fs")
const postcss = require("postcss")
const mvdisplay = require("postcss-multi-value-display")

let css = fs.readFileSync("input.css", "utf8")

let output = postcss()
  .use(mvdisplay)
  .process(css)
  .css

If input.css contains the following:

.card-title {
  display: block flow;
}

.card-items {
  display: inline flex;
}

Then output will be:

.card-title {
  display: block;
}

.card-items {
  display: inline-flex;
}

Supported values

The following 'display' values have CSS level 2 single-value (legacy) equivalents and are supported by this plugin:

• block flow (equivalent to block)
• block flow-root (equivalent to flow-root)
• inline flow (equivalent to inline)
• inline flow-root (equivalent to inline-block)
• run-in flow (equivalent to run-in)
• block flex (equivalent to flex)
• inline flex (equivalent to inline-flex)
• block grid (equivalent to grid)
• inline grid (equivalent to inline-grid)
• inline ruby (equivalent to ruby)
• block table (equivalent to table)
• inline table (equivalent to inline-table)

Note that the two-value versions can be specified in either order (per the W3C spec), so e.g. both inline flex and flex inline will be transformed to inline-flex.

Other values from CSS Display Module Level 3 are not supported. This includes:

• block ruby as there is no single-value equivalent
• any of the multi-value list-item variants
• contents as this value introduces an entirely new semantic which cannot be emulated by transpiling

Also be aware that even among the single-value options which this plugin outputs, browser support is not universal. For example, inline-block is supported as far back as IE 8, but flow-root is unsupported in IE and in EdgeHTML-based (i.e. pre-Chromium) MS Edge versions.

Options

This plugin can optionally be configured by passing in an options object, like this:

const postcss = require("postcss")
const mvdisplay = require("postcss-multi-value-display")

const options = { ... }

postcss.use(mvdisplay(options)).process(...)

Allowed options are:

preserve (default: false)

Keep two-value 'display' declarations but emit the appropriate single-value legacy syntax as a separate declaration above each. Browsers skip over declarations whose values they don't understand, so new browsers will use the latter line (overriding the former) while older ones will use the former and skip the latter.

This should generally never be necessary as the old values are completely equivalent to the new ones. In theory this means adding { preserve: true } will not change any browsers' behavior and will only serve to bloat your output CSS.

Warnings

This plugin will issue a warning if it encounters a display declaration with a multi-token value that it doesn't recognize. For example, if your CSS includes display: block ruby; somewhere and you run PostCSS from the CLI, you'd see a message like this:

6:3 ⚠  Cannot transform 'display: block ruby' (no legacy equivalent exists). [postcss-multi-value-display]

License

This repository is made available under the MIT license; see the included LICENSE file for details.