PostCSS Blank Pseudo

PostCSS Blank Pseudo lets you style form elements when they are empty, following the Selectors Level 4 specification.

input:blank {
    background-color: yellow;
}

/* becomes */

input[blank].js-blank-pseudo, .js-blank-pseudo input[blank] {
    background-color: yellow;
}
input:blank {
    background-color: yellow;
}

Usage

Add PostCSS Blank Pseudo to your project:

npm install postcss css-blank-pseudo --save-dev

Use it as a PostCSS plugin:

const postcss = require('postcss');
const postcssBlankPseudo = require('css-blank-pseudo');

postcss([
    postcssBlankPseudo(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);

PostCSS Blank Pseudo runs in all Node environments, with special instructions for:

Options

preserve

The preserve option determines whether the original notation is preserved. By default, it is preserved.

postcssBlankPseudo({ preserve: false })

input:blank {
    background-color: yellow;
}

/* becomes */

input[blank].js-blank-pseudo, .js-blank-pseudo input[blank] {
    background-color: yellow;
}

replaceWith

The replaceWith option determines the selector to use when replacing the :blank pseudo. By default is [blank]

postcssBlankPseudo({ replaceWith: '.css-blank' })

input:blank {
    background-color: yellow;
}

/* becomes */

.foo {
    color: blue;
    color: red;
}

.baz {
    color: green;
}

Note that changing this option implies that it needs to be passed to the browser polyfill as well.

Browser

import cssBlankPseudoInit from 'css-blank-pseudo/browser';

cssBlankPseudoInit();

or

<!-- When using a CDN url you will have to manually update the version number -->
<script src="https://unpkg.com/css-blank-pseudo@3.0.3/dist/browser-global.js"></script>
<script>cssBlankPseudoInit()</script>

PostCSS Blank Pseudo works in all major browsers, including Safari 6+ and Internet Explorer 9+ without any additional polyfills.

This plugin conditionally uses MutationObserver to ensure recently inserted inputs get correct styling upon insertion. If you intend to rely on that behaviour for browsers that do not support MutationObserver, you have two options:

1. Polyfill MutationObserver. As long as it runs before cssBlankPseudoInit, the polyfill will work.
2. If you don't want to polyfill MutationObserver you can also manually fire a change event upon insertion so they're automatically inspected by the polyfill.

Browser Usage

force

The force option determines whether the library runs even if the browser supports the selector or not. By default, it won't run if the browser does support the selector.

cssBlankPseudoInit({ force: true });

replaceWith

Similar to the option for the PostCSS Plugin, replaceWith determines the attribute or class to apply to an element when it's considered to be :blank.

cssBlankPseudoInit({ replaceWith: '.css-blank' });

This option should be used if it was changed at PostCSS configuration level. Please note that using a class, leverages classList under the hood which might not be supported on some old browsers such as IE9, so you may need to polyfill classList in those cases.