Description

Add support flexible themes for svelte components.

You can use this plugin with rollup-plugin-svelte: svelte({ preprocessor: ... })

Plugin support these CSS syntaxes: scss, less, stylus, js

Install

npm i postcss postcss-import node-sass svelte-preprocess svelte-themes-preprocess --save-dev

How it work

theme_dark.scss

:global(.theme_dark) {
    @if ($component = 'module_name/src/components/Nav') {
        h1 {
            color: #111;
        }
    }
}

theme_light.scss

:global(.theme_light) {
    @if ($component = 'module_name/src/routes/index') {
        h1 {
            color: #222;
        }
    }
}

themes.scss

@import 'themes/theme_dark';
@import 'themes/theme_light';

component.svelte

<h1>Svelte component</h1>
<style>
    h1 {
        color: #000;
    }
</style>

Preprocessing

import preprocess from 'svelte-preprocess'
import postcssImport from 'postcss-import'
import themesPreprocess from 'svelte-themes-preprocess'

const postcssOptions = {
    plugins: [
        // This plugin is necessary and should be first in plugins list:
        postcssImport(),

        // Other plugins ...
    ]
}

const sveltePreprocess = preprocess({
    scss   : true,
    postcss: postcssOptions
})

const result = svelte.preprocess(input, themesPreprocess(
    path.resolve('./src/styles/themes.scss'),
    sveltePreprocess,
    {
        lang: 'scss',
        debug: {
            showComponentsIds: true // show components ids in console
        },
        langs: { // (Optional) if you want to use custom CSS preprocessor
            js(componentId, themesPath) {
                return `
                    var themeBuilder = require('${themesPath.replace(/'/g, '\'')}')
                    if (themeBuilder.__esModule) {
                        themeBuilder = themeBuilder.default
                    }
                    module.exports = themeBuilder('${componentId.replace(/'/g, '\'')}')
                `
            },
            less(componentId, themesPath) {
                return '\r\n'
                    + `@component: '${componentId.replace(/'/g, '\'')}';\r\n`
                    + `@import '${themesPath.replace(/'/g, '\'')}';\r\n`
            }
        }
    }
))

Result

<h1>Svelte component</h1>
<style>
    h1 {
        color: #000;
    }

    .theme_dark h1 {
        color: #111;
    }

    .theme_light h1 {
        color: #222;
    }
</style>

License

CC0-1.0