IE11 - does a polyfill / script exist for CSS variables?

Question

I'm developing a webpage in a mixed web browser environment (Chrome/IE11). IE11 doesn't support CSS variables, is there a polyfill or script that exists that would allow me to use CSS variables in IE11?

Answer 1

Yes, so long as you're processing root-level custom properties (IE9+).

• GitHub: https://github.com/jhildenbiddle/css-vars-ponyfill
• NPM: https://www.npmjs.com/package/css-vars-ponyfill
• Demo: https://codepen.io/jhildenbiddle/pen/ZxYJrR

From the README:

Features

• Client-side transformation of CSS custom properties to static values
• Live updates of runtime values in both modern and legacy browsers
• Transforms <link>, <style>, and @import CSS
• Transforms relative url() paths to absolute URLs
• Supports chained and nested var() functions
• Supports var() function fallback values
• Supports web components / shadow DOM CSS
• Watch mode auto-updates on <link> and <style> changes
• UMD and ES6 module available
• TypeScript definitions included
• Lightweight (6k min+gzip) and dependency-free

Limitations

• Custom property support is limited to :root and :host declarations
• The use of var() is limited to property values (per W3C specification)

Here are a few examples of what the library can handle:

Root-level custom properties

:root {
    --a: red;
}

p {
    color: var(--a);
}

Chained custom properties

:root {
    --a: var(--b);
    --b: var(--c);
    --c: red;
}

p {
    color: var(--a);
}

Nested custom properties

:root {
    --a: 1em;
    --b: 2;
}

p {
    font-size: calc(var(--a) * var(--b));
}

Fallback values

p {
    font-size: var(--a, 1rem);
    color: var(--b, var(--c, var(--d, red))); 
}

Transforms <link>, <style>, and @import CSS

<link rel="stylesheet" href="/absolute/path/to/style.css">
<link rel="stylesheet" href="../relative/path/to/style.css">

<style>
    @import "/absolute/path/to/style.css";
    @import "../relative/path/to/style.css";
</style>

Transforms web components / shadow DOM

<custom-element>
  #shadow-root
    <style>
      .my-custom-element {
        color: var(--test-color);
      }
    </style>
    <div class="my-custom-element">Hello.</div>
</custom-element>

For the sake of completeness: w3c specs

(Shameless self-promotion: Check)

Answer 2

This polyfill enables almost complete support for Custom Properties (not only root-level) in IE11:
https://github.com/nuxodin/ie11CustomProperties

How it works

The script makes use of the fact that IE has minimal custom properties support where properties can be defined and read out with the cascade in mind.
.myEl {-ie-test:'aaa'} // only one dash allowed! "-"
then read it in javascript:
getComputedStyle( querySelector('.myEl') )['-ie-test']

Features from the README:

• handles dynamic added html-content
• handles dynamic added <style>, <link>-elements
• chaining --bar:var(--foo)
• fallback var(--color, blue)
• :focus, :target, :hover
• js-integration:
  • style.setProperty('--x','y')
  • style.getPropertyValue('--x')
  • getComputedStyle(el).getPropertyValue('--inherited')
• Inline styles: <div ie-style="--color:blue"...
• cascade works
• inheritance works
• under 3k (min+gzip) and dependency-free

Demo:

https://rawcdn.githack.com/nuxodin/ie11CustomProperties/b851ec2b6b8e336a78857b570d9c12a8526c9a91/test.html

Answer 3

+1 for the code-pen snippet link in the question comment section above by [I has kode]. One thing I found though is the snippet needs to be slightly modified to have the function declarations defined in the JSON format for IE11 to not complain. Below is the slightly modified version of the code pen snippet:

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() {
        let styleBlocks = document.querySelectorAll('style:not(.inserted),link[type="text/css"]');

        // we need to track the order of the style/link elements when we save off the CSS, set a counter
        let counter = 1;

        // loop through all CSS blocks looking for CSS variables being set
        [].forEach.call(styleBlocks, function (block) {
            // console.log(block.nodeName);
            let 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);
        cssVarPoly.varsByBlock[counter] = theCSS.match(/(--.+:.+;)/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 (let curCSSID in cssVarPoly.oldCSS) {
            // console.log("curCSS:",oldCSS[curCSSID]);
            let 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 (let theVar in varList) {
            // console.log(theVar);
            // match the variable with the actual variable name
            let 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
            let getterRegex2 = new RegExp('var\\(\\s*.+\\s*,\\s*(.+)\\)', 'g');
            // console.log(getterRegex);
            // console.log(curCSS);
            let 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 (let curBlock in varList) {
            let 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
                let 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(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();

Answer 4

I tried this version of Polyfill but ended up with errors when one line in CSS had multiple variables (FI font and color). A colleague of mine helped me out. See line 94.

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() {
        let styleBlocks = document.querySelectorAll('style:not(.inserted),link[type="text/css"]');

        // we need to track the order of the style/link elements when we save off the CSS, set a counter
        let counter = 1;

        // loop through all CSS blocks looking for CSS variables being set
        [].forEach.call(styleBlocks, function (block) {
            // console.log(block.nodeName);
            let 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);
        cssVarPoly.varsByBlock[counter] = theCSS.match(/(--.+:.+;)/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 (let curCSSID in cssVarPoly.oldCSS) {
            // console.log("curCSS:",oldCSS[curCSSID]);
            let 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 (let theVar in varList) {
            // console.log(theVar);
            // match the variable with the actual variable name
            // console.log (theVar);
            var res = theVar.match(/--[a-zA-Z0-9-]+/g);
            // console.log (res[0]);
            theVar = res[0];
            let 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
            let getterRegex2 = new RegExp('var\\(\\s*.+\\s*,\\s*(.+)\\)', 'g');
            // console.log(getterRegex);
            // console.log(curCSS);
            let 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 (let curBlock in varList) {
            let 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
                let 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(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();

Answer 5

To support Internet Explorer, Just use the below script in index.html head tag and it's working like a charm.

<script>window.MSInputMethodContext && document.documentMode && document.write('<script src="https://cdn.jsdelivr.net/gh/nuxodin/ie11CustomProperties@4.1.0/ie11CustomProperties.min.js"><\x2fscript>');</script>