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css-var-polyfill.js
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css-var-polyfill.js
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/*!
* css-var-polyfill.js - v1.2
*
* Copyright (c) 2019 Aaron Barker <http://aaronbarker.net>
* Released under the MIT license
*
* Date: 2021-03-19
*/
let cssVarPoly = {
init: function() {
// first lets see if the browser supports CSS variables
// No version of IE supports window.CSS.supports, so if that isn't supported in the first place we know CSS variables is not supported
// Edge supports supports, so check for actual variable support
if (window.CSS && window.CSS.supports && window.CSS.supports('(--foo: red)')) {
// this browser does support variables, abort
console.log('your browser supports CSS variables, aborting and letting the native support handle things.');
return;
} else {
// edge barfs on console statements if the console is not open... lame!
console.log('no support for you! polyfill all (some of) the things!!');
document.querySelector('body').classList.add('cssvars-polyfilled');
}
cssVarPoly.ratifiedVars = {};
cssVarPoly.varsByBlock = {};
cssVarPoly.oldCSS = {};
// start things off
cssVarPoly.findCSS();
cssVarPoly.updateCSS();
},
// find all the css blocks, save off the content, and look for variables
findCSS: function() {
var styleBlocks = document.querySelectorAll('style:not(.inserted),link[rel="stylesheet"],link[rel="import"]');
// we need to track the order of the style/link elements when we save off the CSS, set a counter
var counter = 1;
// loop through all CSS blocks looking for CSS variables being set
[].forEach.call(styleBlocks, function(block) {
// console.log(block.nodeName);
var theCSS;
if (block.nodeName === 'STYLE') {
// console.log("style");
theCSS = block.innerHTML;
cssVarPoly.findSetters(theCSS, counter);
} else if (block.nodeName === 'LINK') {
// console.log("link");
cssVarPoly.getLink(block.getAttribute('href'), counter, function(counter, request) {
cssVarPoly.findSetters(request.responseText, counter);
cssVarPoly.oldCSS[counter] = request.responseText;
cssVarPoly.updateCSS();
});
theCSS = '';
}
// save off the CSS to parse through again later. the value may be empty for links that are waiting for their ajax return, but this will maintain the order
cssVarPoly.oldCSS[counter] = theCSS;
counter++;
});
},
// find all the "--variable: value" matches in a provided block of CSS and add them to the master list
findSetters: function(theCSS, counter) {
// console.log(theCSS);
// tests for the following at https://regex101.com/r/kWwUmp/3
cssVarPoly.varsByBlock[counter] = theCSS.match(/(--[\w-]+:[\s]*[^;\n}]+)/g) || [];
},
// run through all the CSS blocks to update the variables and then inject on the page
updateCSS: function() {
// first lets loop through all the variables to make sure later vars trump earlier vars
cssVarPoly.ratifySetters(cssVarPoly.varsByBlock);
// loop through the css blocks (styles and links)
for (var curCSSID in cssVarPoly.oldCSS) {
// console.log("curCSS:", cssVarPoly.oldCSS[curCSSID]);
var newCSS = cssVarPoly.replaceGetters(cssVarPoly.oldCSS[curCSSID], cssVarPoly.ratifiedVars);
// put it back into the page
// first check to see if this block exists already
if (document.querySelector('#inserted' + curCSSID)) {
// console.log("updating")
document.querySelector('#inserted' + curCSSID).innerHTML = newCSS;
} else {
// console.log("adding");
var style = document.createElement('style');
style.type = 'text/css';
style.innerHTML = newCSS;
style.classList.add('inserted');
style.id = 'inserted' + curCSSID;
document.getElementsByTagName('head')[0].appendChild(style);
}
};
},
// parse a provided block of CSS looking for a provided list of variables and replace the --var-name with the correct value
replaceGetters: function(curCSS, varList) {
// console.log(varList);
for (var theVar in varList) {
// console.log(theVar);
// match the variable with the actual variable name
var getterRegex = new RegExp('var\\(\\s*' + theVar + '\\s*\\)', 'g');
// console.log(getterRegex);
// console.log(curCSS);
curCSS = curCSS.replace(getterRegex, varList[theVar]);
// now check for any getters that are left that have fallbacks
var getterRegex2 = new RegExp('var\\([^\\)]+,\\s*([^\\)]+)\\)', 'g');
// console.log(getterRegex);
// console.log(curCSS);
var matches = curCSS.match(getterRegex2);
if (matches) {
// console.log("matches",matches);
matches.forEach(function(match) {
// console.log(match.match(/var\(.+,\s*(.+)\)/))
// find the fallback within the getter
curCSS = curCSS.replace(match, match.match(/var\([^\)]+,\s*([^\)]+)\)/)[1]);
});
}
// curCSS = curCSS.replace(getterRegex2,varList[theVar]);
};
// console.log(curCSS);
return curCSS;
},
// determine the css variable name value pair and track the latest
ratifySetters: function(varList) {
// console.log("varList:",varList);
// loop through each block in order, to maintain order specificity
for (var curBlock in varList) {
var curVars = varList[curBlock];
// console.log("curVars:",curVars);
// loop through each var in the block
curVars.forEach(function(theVar) {
// console.log(theVar);
// split on the name value pair separator
var matches = theVar.split(/:\s*/);
// console.log(matches);
// put it in an object based on the varName. Each time we do this it will override a previous use and so will always have the last set be the winner
// 0 = the name, 1 = the value, strip off the ; if it is there
cssVarPoly.ratifiedVars[matches[0]] = matches[1].replace(/;/, '');
});
};
// console.log(cssVarPoly.ratifiedVars);
},
// get the CSS file (same domain for now)
getLink: function(url, counter, success) {
var request = new XMLHttpRequest();
request.open('GET', url, true);
request.overrideMimeType('text/css;');
request.onload = function() {
if (request.status >= 200 && request.status < 400) {
// Success!
// console.log(request.responseText);
if (typeof success === 'function') {
success(counter, request);
}
} else {
// We reached our target server, but it returned an error
console.warn('an error was returned from:', url);
}
};
request.onerror = function() {
// There was a connection error of some sort
console.warn('we could not get anything from:', url);
};
request.send();
}
};
cssVarPoly.init();