IE11-CSS変数用のポリフィル/スクリプトは存在しますか？

混合Webブラウザ環境（Chrome / IE11）でWebページを開発しています。IE11はCSS変数をサポートしていませんが、IE11でCSS変数を使用できるようにするポリフィルまたはスクリプトは存在しますか？

はい、ルートレベルのカスタムプロパティ（IE9 +）を処理している限り可能です。

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

READMEから：

特徴

• CSSカスタムプロパティの静的な値へのクライアント側の変換
• 最新のブラウザと従来のブラウザの両方でのランタイム値のライブアップデート
• トランスフォーム<link>、<style>および@importCSS
• 相対url()パスを絶対URLに変換します
• 連鎖var()関数と入れ子関数をサポートします
• var()関数フォールバック値をサポートします
• Webコンポーネント/シャドウDOMCSSをサポート
• ウォッチモードの自動更新<link>と<style>変更
• UMDおよびES6モジュールが利用可能
• TypeScript定義が含まれています
• 軽量（6k min + gzip）で依存関係がありません

制限事項

• カスタムプロパティのサポートは:root、:host宣言に
• var（）の使用は、プロパティ値に制限されています（W3C仕様による）

ライブラリが処理できるもののいくつかの例を次に示します。

ルートレベルのカスタムプロパティ

:root {
    --a: red;
}

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

連鎖カスタムプロパティ

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

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

ネストされたカスタムプロパティ

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

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

フォールバック値

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

トランスフォーム<link>、<style>および@importCSS

<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>

Webコンポーネント/シャドウDOMを変換します

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

完全を期すために：w3c仕様

お役に立てれば。

（恥知らずな自己宣伝：チェック）

このポリフィルにより、IE11のカスタムプロパティ（ルートレベルだけでなく）のほぼ完全なサポートが可能になります：https：
//github.com/nuxodin/ie11CustomProperties

使い方

このスクリプトは、IEが最小限のカスタムプロパティをサポートしているという事実を利用しており、カスケードを念頭に置いてプロパティを定義して読み取ることができます。
.myEl {-ie-test:'aaa'} // only one dash allowed! "-"
次に、JavaScriptでそれを読みます。
getComputedStyle( querySelector('.myEl') )['-ie-test']

READMEの機能：

• 動的に追加されたhtmlコンテンツを処理します
• ハンドル動的加え<style>、<link>-elements
• チェーン --bar:var(--foo)
• 後退する var(--color, blue)
• ：focus、：target、：hover
• js-統合：
  • style.setProperty('--x','y')
  • style.getPropertyValue('--x')
  • getComputedStyle(el).getPropertyValue('--inherited')
• インラインスタイル： <div ie-style="--color:blue"...
• カスケード動作
• 継承は機能します
• 3k（min + gzip）未満で依存関係なし

デモ：

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

[I haskode]による上記の質問コメントセクションのコードペンスニペットリンクの+1。私が見つけた1つのことは、IE11が文句を言わないように、関数宣言をJSON形式で定義するようにスニペットを少し変更する必要があるということです。以下は、コードペンスニペットのわずかに変更されたバージョンです。

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();

このバージョンのPolyfillを試しましたが、CSSの1行に複数の変数（FIフォントと色）があるとエラーが発生しました。私の同僚が私を助けてくれました。94行目を参照してください。

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();

Internet Explorerをサポートするには、index.htmlヘッドタグで以下のスクリプトを使用するだけで、チャームのように機能します。

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