Created
January 2, 2020 05:37
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Exploring one way CSS stylesheet authors can express that certain styles conditionally depend on other CSS stylesheets or JS files being present for them to work. Online demo: http://staticresource.com/cdr.html
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| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <meta name="viewport" content="width=device-width, initial-scale=1"> | |
| <title>CSS Dependency Resolver Demo</title> | |
| <h1>CSS Dependency Resolver</h1> | |
| <style> | |
| @supports (--dependencies(url(https://csspl.us/cursory.js))) { | |
| * { | |
| cursor: none; | |
| } | |
| :root::before { | |
| content: ''; | |
| display: block; | |
| width: 30px; | |
| height: 30px; | |
| border-radius: 0% 100% 25% 75% / 0% 75% 25% 100%; | |
| position: fixed; | |
| background: black; | |
| top: calc(var(--cursorY) * 1px); | |
| left: calc(var(--cursorX) * 1px); | |
| pointer-events: none; | |
| } | |
| } | |
| </style> | |
| <script type=module src=css-dependency-resolver.js></script> |
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| // CSS Dependency Resolver | |
| // @supports --dependencies(url() url('') url("")) {} | |
| // @supports (--dependencies(url() url('') url(""))) {} | |
| import {process, all, add} from 'https://unpkg.com/cssomtools' | |
| import * as parseCSS from 'https://tomhodgins.github.io/parse-css/index.js' | |
| process(all(), cssomRule => { | |
| const parsedRule = parseCSS.parseARule(cssomRule.cssText) | |
| const prelude = parseCSS.parseAListOfComponentValues(cssomRule.conditionText) | |
| const urlFilter = list => list.filter(({tokenType, type}) => tokenType === 'URL' || type === 'FUNCTION') | |
| // @supports () {} | |
| const supportsAtRule = parsedRule.type === 'AT-RULE' | |
| && parsedRule.name === 'supports' | |
| && prelude | |
| // --dependencies() | |
| const plainFunction = prelude[0] | |
| && prelude[0].type === 'FUNCTION' | |
| && prelude[0].name === '--dependencies' | |
| && prelude[0].value | |
| && urlFilter(prelude[0].value).length | |
| // (--dependencies()) | |
| const blockWrappedFunction = prelude[0] | |
| && prelude[0].value | |
| && prelude[0].value[0] | |
| && prelude[0].value[0].type === 'FUNCTION' | |
| && prelude[0].value[0].name === '--dependencies' | |
| && prelude[0].value[0].value | |
| && urlFilter(prelude[0].value[0].value).length | |
| if ( | |
| supportsAtRule | |
| && (plainFunction || blockWrappedFunction) | |
| ) { | |
| const parent = cssomRule.parentRule | |
| ? cssomRule.parentRule | |
| : cssomRule.parentStyleSheet | |
| const tokens = plainFunction | |
| ? prelude[0].value | |
| : prelude[0].value[0].value | |
| const urls = urlFilter(tokens).map(token => | |
| Array.isArray(token.value) | |
| ? token.value[0].value | |
| : token.value | |
| ) | |
| urls.forEach(async url => { | |
| const extension = new URL(url).pathname.match(/\.\w+$/) | |
| ? new URL(url).pathname.match(/\.\w+$/)[0] | |
| : '.css' | |
| // Fetch and inline CSS | |
| if (extension === '.css') { | |
| let link = document.querySelector(`link[rel="stylesheet"][href*="${url}"]`) | |
| if (link === null) { | |
| link = document.createElement('link') | |
| link.rel = 'stylesheet' | |
| link.href = url | |
| document.documentElement.prepend(link) | |
| } | |
| } | |
| // Add any JS dependencies not found | |
| if (extension === '.js') { | |
| let script = document.querySelector(`script[src*="${url}"]`) | |
| if (script === null) { | |
| script = document.createElement('script') | |
| script.src = url | |
| script.type = 'module' | |
| document.documentElement.append(script) | |
| } | |
| } | |
| }) | |
| // Add child CSS rules after dependencies have been added | |
| add( | |
| Array.from(cssomRule.cssRules), | |
| parent, | |
| Array.from(parent.cssRules).indexOf(cssomRule) | |
| ) | |
| // Remove original @supports rule | |
| cssomRule.parentStyleSheet.deleteRule( | |
| Array.from(parent.cssRules).indexOf(cssomRule) | |
| ) | |
| } | |
| }) |
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