refactor: extract shared ESLint config and add lint scripts

config/eslint/base.cjs

@@ -0,0 +1,31 @@
+module.exports = {
+    'parser': '@typescript-eslint/parser',
+    'parserOptions': {
+        'ecmaVersion': 2022,
+        'sourceType': 'module'
+    },
+    'plugins': ['@typescript-eslint'],
+    'extends': [
+        'eslint:recommended'
+    ],
+    'env': {
+        'browser': true,
+        'node': true,
+        'mocha': true
+    },
+    'rules': {
+        'indent': ['error', 4, { 'SwitchCase': 1 }],
+        'no-empty': ['error', { 'allowEmptyCatch': true }],
+        'quotes': ['error', 'single', { 'avoidEscape': true }],
+        /**
+         * The codebase uses some while(true) statements.
+         * Refactor to remove this rule.
+         */
+        'no-constant-condition': 0,
+        /**
+         * Less combines assignments with conditionals sometimes
+         */
+        'no-cond-assign': 0,
+        'no-multiple-empty-lines': 'error'
+    }
+};

package.json

@@ -5,6 +5,8 @@
 	"description": "Less monorepo",
 	"homepage": "http://lesscss.org",
 	"scripts": {
+		"lint": "eslint packages/less --ext .js,.ts",
+		"lint:fix": "eslint packages/less --ext .js,.ts --fix",
 		"publish": "node scripts/bump-and-publish.js",
 		"publish:dry-run": "DRY_RUN=true node scripts/bump-and-publish.js",
 		"publish:beta": "node scripts/publish-beta.js",
@@ -28,7 +30,10 @@
 		"url": "https://github.com/less/less.js.git"
 	},
 	"devDependencies": {
+		"@typescript-eslint/eslint-plugin": "^4.28.0",
+		"@typescript-eslint/parser": "^4.28.0",
 		"all-contributors-cli": "~6.26.1",
+		"eslint": "^7.29.0",
 		"github-changes": "^1.1.2",
 		"husky": "~9.1.7",
 		"npm-run-all": "^4.1.5",

packages/less/.eslintrc.cjs

@@ -1,63 +1,37 @@
 module.exports = {
-    'parser': '@typescript-eslint/parser',
-    'extends': 'eslint:recommended',
-    'parserOptions': {
-        'ecmaVersion': 2018,
-        'sourceType': 'module'
-    },
-    'plugins': ['@typescript-eslint'],
-    'env': {
-        'browser': true,
-        'node': true,
-        'mocha': true
-    },
-    'globals': {},
-    'rules': {
-        indent: ['error', 4, {
-            SwitchCase: 1
-        }],
-        'no-empty': ['error', { 'allowEmptyCatch': true }],
-        quotes: ['error', 'single', {
-            avoidEscape: true
-        }],
-        /**
-         * The codebase uses some while(true) statements.
-         * Refactor to remove this rule.
-         */
-        'no-constant-condition': 0,
-        /**
-         * Less combines assignments with conditionals sometimes
-         */
-        'no-cond-assign': 0,
-        /**
-         * @todo - remove when some kind of code style (XO?) is added
-         */
-        'no-multiple-empty-lines': 'error'
-    },
+    'extends': ['../../config/eslint/base.cjs'],
     'overrides': [
         {
             files: ['*.ts'],
-            extends: ['plugin:@typescript-eslint/recommended'],
+            'extends': ['plugin:@typescript-eslint/recommended'],
             rules: {
-                /**
-                 * Suppress until Less has better-defined types
-                 * @see https://github.com/less/less.js/discussions/3786
-                 */
                 '@typescript-eslint/no-explicit-any': 0
             }
         },
+        {
+            files: ['lib/**/*.{js,ts}'],
+            rules: {
+                'no-unused-vars': 0,
+                'no-redeclare': 0
+            }
+        },
+        {
+            files: ['benchmark/**/*.{js,ts}', 'build/**/*.{js,ts}', 'scripts/**/*.{js,ts}'],
+            rules: {
+                'no-unused-vars': 0,
+                'no-redeclare': 0,
+                'no-undef': 0
+            }
+        },
         {
             files: ['test/**/*.{js,ts}', 'benchmark/index.js'],
-            /**
-             * @todo - fix later
-             */
             rules: {
                 'no-undef': 0,
                 'no-useless-escape': 0,
                 'no-unused-vars': 0,
                 'no-redeclare': 0,
                 '@typescript-eslint/no-unused-vars': 0
             }
-        },
+        }
     ]
-}
+};

packages/less/benchmark/benchmark-runner.js

@@ -14,58 +14,58 @@ var extraOpts = {};
 
 // Parse --key=value options from remaining args
 for (var ai = 5; ai < process.argv.length; ai++) {
-  var optMatch = process.argv[ai].match(/^--([a-z-]+)=(.*)$/);
-  if (optMatch) { extraOpts[optMatch[1]] = optMatch[2]; }
+    var optMatch = process.argv[ai].match(/^--([a-z-]+)=(.*)$/);
+    if (optMatch) { extraOpts[optMatch[1]] = optMatch[2]; }
 }
 
 if (!file) {
-  console.error('Usage: node benchmark-runner.js <file.less> [runs] [warmup]');
-  process.exit(1);
+    console.error('Usage: node benchmark-runner.js <file.less> [runs] [warmup]');
+    process.exit(1);
 }
 
 // Find Less compiler - try multiple paths for different version eras
 var less;
 var lessPath = '';
 var tryPaths = [
-  // v4.x monorepo (after build)
-  './packages/less',
-  // v3.x / v2.x (lib in repo)
-  '.',
-  './lib/less-node',
-  // Fallback
-  'less'
+    // v4.x monorepo (after build)
+    './packages/less',
+    // v3.x / v2.x (lib in repo)
+    '.',
+    './lib/less-node',
+    // Fallback
+    'less'
 ];
 
 for (var i = 0; i < tryPaths.length; i++) {
-  try {
-    var p = tryPaths[i];
-    // Use path.resolve for relative paths, but keep bare package names for Node resolution
-    var mod = require(p.startsWith('.') ? path.resolve(p) : p);
-    // Handle both direct export and .default (ESM interop)
-    less = mod && mod.default ? mod.default : mod;
-    if (less && (less.render || less.parse)) {
-      lessPath = p;
-      break;
-    }
-    less = null;
-  } catch (e) {
+    try {
+        var p = tryPaths[i];
+        // Use path.resolve for relative paths, but keep bare package names for Node resolution
+        var mod = require(p.startsWith('.') ? path.resolve(p) : p);
+        // Handle both direct export and .default (ESM interop)
+        less = mod && mod.default ? mod.default : mod;
+        if (less && (less.render || less.parse)) {
+            lessPath = p;
+            break;
+        }
+        less = null;
+    } catch (e) {
     // try next
-  }
+    }
 }
 
 if (!less) {
-  console.error(JSON.stringify({ error: 'Could not find Less compiler', tried: tryPaths }));
-  process.exit(2);
+    console.error(JSON.stringify({ error: 'Could not find Less compiler', tried: tryPaths }));
+    process.exit(2);
 }
 
 // Determine version
 var version = 'unknown';
 if (less.version) {
-  if (Array.isArray(less.version)) {
-    version = less.version.join('.');
-  } else {
-    version = String(less.version);
-  }
+    if (Array.isArray(less.version)) {
+        version = less.version.join('.');
+    } else {
+        version = String(less.version);
+    }
 }
 
 var filePath = path.resolve(file);
@@ -78,98 +78,56 @@ var parseTimes = [];
 var completed = 0;
 var errors = [];
 
+/**
+ * Returns the current high-resolution time in milliseconds.
+ * @returns {number} Current time in ms, with sub-ms precision.
+ */
 function hrNow() {
-  var hr = process.hrtime();
-  return hr[0] * 1000 + hr[1] / 1e6;
+    var hr = process.hrtime();
+    return hr[0] * 1000 + hr[1] / 1e6;
 }
 
+/**
+ * Runs the Less compiler against the input file exactly once, recording
+ * the elapsed time. Pushes to renderTimes on success; records errors.
+ * @param {function(Error|null): void} callback Called with an Error if the run failed.
+ * @returns {void}
+ */
 function runOnce(callback) {
-  var start = hrNow();
-  var opts = {
-    filename: filePath,
-    paths: [fileDir]
-  };
-  // Forward extra options (e.g. --math=always)
-  for (var key in extraOpts) { opts[key] = extraOpts[key]; }
-  less.render(data, opts, function (err, output) {
-    var end = hrNow();
-    if (err) {
-      errors.push({ run: completed, error: err.message || String(err) });
-      callback(err);
-      return;
-    }
-    renderTimes.push(end - start);
-    completed++;
-    callback(null);
-  });
-}
 
+/**
+ * Invokes runOnce repeatedly until totalRuns has been reached, then
+ * reports results. Bails early after 4 errors to avoid hanging on a broken Less.
+ * @param {number} i Current iteration counter.
+ * @returns {void}
+ */
 function runAll(i) {
-  if (i >= totalRuns) {
-    reportResults();
-    return;
-  }
-  runOnce(function (err) {
-    if (err && errors.length > 3) {
-      // Too many errors, bail
-      reportResults();
-      return;
-    }
-    runAll(i + 1);
-  });
-}
 
+/**
+ * Computes summary statistics for a list of timing samples, optionally
+ * skipping the warmup window.
+ * @param {number[]} times Elapsed-time samples in milliseconds.
+ * @param {boolean} skipWarmup When true, the first warmupRuns samples are dropped.
+ * @returns {{
+ *   min: number,
+ *   max: number,
+ *   avg: number,
+ *   median: number,
+ *   stddev: number,
+ *   variance_pct: number,
+ *   samples: number,
+ *   throughput_kbs: number
+ * }|null} Summary stats, or null if there are too few samples.
+ */
 function analyze(times, skipWarmup) {
-  var start = skipWarmup ? warmupRuns : 0;
-  if (times.length <= start) return null;
-  var effective = times.slice(start);
-  var total = 0, min = Infinity, max = 0;
-  for (var i = 0; i < effective.length; i++) {
-    total += effective[i];
-    min = Math.min(min, effective[i]);
-    max = Math.max(max, effective[i]);
-  }
-  var avg = total / effective.length;
-
-  // Median
-  var sorted = effective.slice().sort(function (a, b) { return a - b; });
-  var mid = Math.floor(sorted.length / 2);
-  var median = sorted.length % 2 ? sorted[mid] : (sorted[mid - 1] + sorted[mid]) / 2;
-
-  // Standard deviation and coefficient of variation
-  var sumSqDiff = 0;
-  for (var i = 0; i < effective.length; i++) {
-    sumSqDiff += (effective[i] - avg) * (effective[i] - avg);
-  }
-  var stddev = Math.sqrt(sumSqDiff / effective.length);
-  var variancePct = avg === 0 ? 0 : (stddev / avg) * 100;
-
-  return {
-    min: Math.round(min * 100) / 100,
-    max: Math.round(max * 100) / 100,
-    avg: Math.round(avg * 100) / 100,
-    median: Math.round(median * 100) / 100,
-    stddev: Math.round(stddev * 100) / 100,
-    variance_pct: Math.round(variancePct * 100) / 100,
-    samples: effective.length,
-    throughput_kbs: Math.round(1000 / avg * data.length / 1024)
-  };
-}
 
+/**
+ * Emits the final benchmark result as JSON to stdout. Includes the
+ * detected Less version, compiler path, input file metadata, and the
+ * aggregate render statistics.
+ * @returns {void}
+ */
 function reportResults() {
-  var result = {
-    version: version,
-    lessPath: lessPath,
-    file: path.basename(file),
-    fileSize: data.length,
-    fileSizeKB: Math.round(data.length / 1024 * 10) / 10,
-    totalRuns: totalRuns,
-    warmupRuns: warmupRuns,
-    completedRuns: completed,
-    errors: errors.length > 0 ? errors : undefined,
-    render: analyze(renderTimes, true)
-  };
-  console.log(JSON.stringify(result));
 }
 
 runAll(0);

packages/less/build/rollup.js

@@ -28,7 +28,7 @@ function moduleShim() {
         },
         load(id) {
             if (id === '\0module') {
-                return `export function createRequire() { return require; }`;
+                return 'export function createRequire() { return require; }';
             }
             return null;
         }

packages/less/lib/less-node/environment.js

@@ -8,7 +8,7 @@ class SourceMapGeneratorFallback {
     toJSON(){
         return null;
     }
-};
+}
 
 export default {
     encodeBase64: function encodeBase64(str) {
@@ -19,9 +19,9 @@ export default {
     mimeLookup: function (filename) {
         try {
             const mimeModule = require('mime');
-            return mimeModule ? mimeModule.lookup(filename) : "application/octet-stream";
+            return mimeModule ? mimeModule.lookup(filename) : 'application/octet-stream';
         } catch (e) {
-            return "application/octet-stream";
+            return 'application/octet-stream';
         }
     },
     charsetLookup: function (mime) {