simple cli tool to strip CSS variables and replace by their declared values so the resulting file becomes CSS3 cross browser compatible

cssVariablesReplacer.js

/**
 * Simple JavaScript CLI helper to strip out CSS Variable from your CSS
 * and pipe this into a new output file which is completely cross browser 
 * compatible.
 *
 * Provided under ISC license:
 *
 * Copyright (c) 2017, Dennis Sterzenbach
 * 
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 * 
 * @author  Dennis Sterzenbach <dennis.sterzenbach@gmail.com>
 */
var fs = require('fs');

let cssFileName;
let outputFileName;
let cssContent;
let verbose = true;
let timingStart = process.hrtime();

let doPrintUsage = false;
let doProcessCSS = true;

if (process.argv.length < 4) {
    doPrintUsage = true;
    doProcessCSS = false;
}

if (doPrintUsage) {
    console.error('Missing Parameters!');
    console.log('Usage: cssVariablesCompiler.js <cssInputFileName> <cssOutputFileName>');
}

cssFileName = process.argv[2];
outputFileName = process.argv[3];

console.log('using files:');
console.log('input          : ', cssFileName);
console.log('output         : ', outputFileName);
console.log('');

if (!cssFileName || cssFileName === '') {
    console.error('missing input file');
    doProcessCSS = false;
}

if (!outputFileName || outputFileName === '') {
    console.error('missing output file');
    doProcessCSS = false;
}

if (doProcessCSS) {
    console.log('');

    cssContent = fs.readFileSync(cssFileName, 'utf-8');
    if (verbose) { 
        console.log('read input file...');
    }

    let {variables:cssVariables, text:strippedString} = stripVariableDeclarations(cssContent);
    if (verbose) { 
        console.log('grabbed CSS variable declarations...');
    }

    let result = replaceVariablesByDeclaredValues(strippedString, cssVariables);
    if (verbose) { 
        console.log('replaced CSS variables by their declared values...');
    }

    fs.writeFileSync(outputFileName, result);
    if (verbose) { 
        console.log('wrote output file.');
        elapsedTime('total runtime');
    }

}

function stripVariableDeclarations(cssContent) {
    let regExp = /([^\(]--[a-zA-Z]+):([^;]+);/gm;
    let input = '--test: xyz;'+"\n"+'--test2: 1rem;';
    let results;
    let variables = {};
    let originalTexts = [];

    input = cssContent;

    while ((results = regExp.exec(input)) !== null) {
        variables[ results[1].trim() ] = results[2].trim();
        originalTexts.push(results[0]);
    }

    for (let i = 0; i < originalTexts.length; i++) {
        cssContent = cssContent.replace(originalTexts[i], '');
    }

    return {
        variables: variables,
        text: cssContent
    };
}

function replaceVariablesByDeclaredValues(cssContent, variables) {
    let findVarUsageRegExp = /var\((--[a-zA-Z]+)\)/gm;
    let input = 'var(--test);'+"\n"+'calc(var(--test2) + 1rem);';
    let strippedString;
    
    input = cssContent;
    strippedString = cssContent;

    // console.log('variables', variables);

    while ((results = findVarUsageRegExp.exec(input)) !== null) {
        let varName = results[1];

        // console.log('varName lookup', varName);
        if (variables && variables[varName]) {
            value = resolveCSSVariable(variables[varName], 1);

            // console.log('varName found', varName, 'value', value);
            strippedString = strippedString.replace(results[0], value);
        }
    }

    function resolveCSSVariable(variable, depth) {
        let findVarUsageRegExp = /var\((--[a-zA-Z]+)\)/gm;

        if (variable && (variable !== '')) {
            if ((depth < 10) && (variable.indexOf('var(') !== -1)) {
                let varDiscoveryResult = findVarUsageRegExp.exec(variable);

                // console.log('resolveCSSVariable', variable, depth, varDiscoveryResult);

                if (varDiscoveryResult === null) {
                    return '';
                }

                return resolveCSSVariable(varDiscoveryResult[1], ++depth);
            }
        }

        if (variables && variables[variable]) {
            return variables[variable];
        }

        // console.log('resolveCSSVariable return', variable, depth);
        return variable;
    }

    return strippedString;
}

function elapsedTime(commentString) {
    let [elapsedSeconds, elapsedNanoseconds] = process.hrtime(timingStart);

    console.log(elapsedSeconds + 's ' + (elapsedNanoseconds / 1000000).toFixed(3) + ' ms' + (commentString ? ' - ' + commentString : ''));
}