A scoped eval plugin for jsincss
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README.md

jsincss-scoped-eval

A scoped eval plugin for jsincss

About

This plugin is a JavaScript module that works with JS-in-CSS stylesheets, to provide JavaScript interpolation inside CSS rules, scoped to each element to which the rule applies.

Downloading

You can download jsincss-scoped-eval and add it to your codebase manually, or download it with npm:

npm install jsincss-scoped-eval

Another option that works for building or testing, that isn't ideal for production use, is linking to the module directly from a CDN like unpkg:

<script type=module>
  import scope from 'https://unpkg.com/jsincss-scoped-eval/index.vanilla.js'
</script>

Importing

This plugin exists in three different formats:

You can import this plugin using the native import statement in JavaScript. Here you can assign any name you want to the function you are importing, and you only need to provide a path to the plugin's index.vanilla.js file:

import scope from './index.vanilla.js'

You can also use the CommonJS-formatted module located at index.js with require() for use with bundlers that don't use vanilla JS modules.

Once you have imported this plugin into your module, you can use the plugin as scope()

Using JS-in-CSS Stylesheets

The main goal of this plugin is to allow CSS authors the ability to use JavaScript interpolation inside the styles they write that are evaluated from the context of the element(s) matching the CSS rules.

The plugin has the following format:

scope(selector, rule)
  • selector is a string containing a CSS selector
  • rule is a string or template string containing a CSS rule, with JavaScript interpolation anywhere using eval('')

Example

This example will use the jsincss plugin to load a JS-in-CSS stylesheet making use of this plugin. To test it in a JavaScript module, import both the jsincss package and any helper plugins you want:

<script type=module>
  import jsincss from 'https://unpkg.com/jsincss/index.vanilla.js'
  import scope from 'https://unpkg.com/jsincss-scoped-eval/index.vanilla.js'

  jsincss(() => `

    ${scope('textarea', `
      background: hsl(eval('this.value.length * 5'), 75%, 75%);
    `)}

  `)
</script>

It's also possible to write your stylesheets as a separate JavaScript module like this, where you import any helper plugins at the top of the stylesheet:

import scope from 'https://unpkg.com/jsincss-scoped-eval/index.vanilla.js'

export default () => `

  ${scope('textarea', `
    background: hsl(eval('this.value.length * 5'), 75%, 75%);
  `)}

`

And then import both the jsincss plugin and the stylesheet into your code and run them like this, suppling any selector or events list the jsincss plugin might need to apply the stylesheet only the the element(s) and event(s) you require, depending on what you're doing:

import jsincss from 'https://unpkg.com/jsincss/index.vanilla.js'
import stylesheet from './path/to/stylesheet.js'

jsincss(stylesheet)

Compatible JS-in-CSS Stylesheet Loaders