diff --git a/lib/__tests__/fixtures/plugin-slashless-warn-about-foo.js b/lib/__tests__/fixtures/plugin-slashless-warn-about-foo.js
index 7ad0d62104..ca2b8f6d64 100644
--- a/lib/__tests__/fixtures/plugin-slashless-warn-about-foo.js
+++ b/lib/__tests__/fixtures/plugin-slashless-warn-about-foo.js
@@ -11,15 +11,13 @@ const warnAboutFooMessages = stylelint.utils.ruleMessages('slashless-warn-about-
 module.exports = stylelint.createPlugin(ruleName, (expectation) => {
 	return (root, result) => {
 		root.walkRules((rule) => {
-			if (rule.selector === '.foo') {
-				if (expectation === 'always') {
-					stylelint.utils.report({
-						result,
-						ruleName,
-						message: warnAboutFooMessages.found,
-						node: rule,
-					});
-				}
+			if (rule.selector === '.foo' && expectation === 'always') {
+				stylelint.utils.report({
+					result,
+					ruleName,
+					message: warnAboutFooMessages.found,
+					node: rule,
+				});
 			}
 		});
 	};
diff --git a/lib/__tests__/fixtures/plugin-warn-about-bar.js b/lib/__tests__/fixtures/plugin-warn-about-bar.js
index 1c601cfa39..b775d1231d 100644
--- a/lib/__tests__/fixtures/plugin-warn-about-bar.js
+++ b/lib/__tests__/fixtures/plugin-warn-about-bar.js
@@ -11,15 +11,13 @@ const warnAboutBarMessages = stylelint.utils.ruleMessages('plugin/warn-about-bar
 module.exports = stylelint.createPlugin(ruleName, (expectation) => {
 	return (root, result) => {
 		root.walkRules((rule) => {
-			if (rule.selector === '.bar') {
-				if (expectation === 'always') {
-					stylelint.utils.report({
-						result,
-						ruleName,
-						message: warnAboutBarMessages.found,
-						node: rule,
-					});
-				}
+			if (rule.selector === '.bar' && expectation === 'always') {
+				stylelint.utils.report({
+					result,
+					ruleName,
+					message: warnAboutBarMessages.found,
+					node: rule,
+				});
 			}
 		});
 	};
diff --git a/lib/__tests__/fixtures/plugin-warn-about-foo.js b/lib/__tests__/fixtures/plugin-warn-about-foo.js
index a6a09ac669..e5698a8342 100644
--- a/lib/__tests__/fixtures/plugin-warn-about-foo.js
+++ b/lib/__tests__/fixtures/plugin-warn-about-foo.js
@@ -11,15 +11,13 @@ const warnAboutFooMessages = stylelint.utils.ruleMessages('plugin/warn-about-foo
 module.exports = stylelint.createPlugin(ruleName, (expectation) => {
 	return (root, result) => {
 		root.walkRules((rule) => {
-			if (rule.selector === '.foo') {
-				if (expectation === 'always') {
-					stylelint.utils.report({
-						result,
-						ruleName,
-						message: warnAboutFooMessages.found,
-						node: rule,
-					});
-				}
+			if (rule.selector === '.foo' && expectation === 'always') {
+				stylelint.utils.report({
+					result,
+					ruleName,
+					message: warnAboutFooMessages.found,
+					node: rule,
+				});
 			}
 		});
 	};
diff --git a/lib/augmentConfig.js b/lib/augmentConfig.js
index bf958eeee1..b39ae13947 100644
--- a/lib/augmentConfig.js
+++ b/lib/augmentConfig.js
@@ -122,7 +122,7 @@ function augmentConfigFull(stylelint, filePath, cosmiconfigResult) {
  */
 function absolutizePaths(config, configDir) {
 	if (config.ignoreFiles) {
-		config.ignoreFiles = /** @type {string[]} */ ([]).concat(config.ignoreFiles).map((glob) => {
+		config.ignoreFiles = /** @type {string[]} */ [config.ignoreFiles].flat().map((glob) => {
 			if (path.isAbsolute(glob.replace(/^!/, ''))) return glob;
 
 			return globjoin(configDir, glob);
@@ -130,7 +130,7 @@ function absolutizePaths(config, configDir) {
 	}
 
 	if (config.plugins) {
-		config.plugins = /** @type {string[]} */ ([]).concat(config.plugins).map((lookup) => {
+		config.plugins = /** @type {string[]} */ [config.plugins].flat().map((lookup) => {
 			return getModulePath(configDir, lookup);
 		});
 	}
@@ -353,8 +353,8 @@ function addProcessorFunctions(config) {
 	/** @type {Array<Function>} */
 	const resultProcessors = [];
 
-	/** @type {Array<StylelintConfigProcessor>} */ ([])
-		.concat(config.processors)
+	/** @type {Array<StylelintConfigProcessor>} */ [config.processors]
+		.flat()
 		.forEach((processorConfig) => {
 			const processorKey = JSON.stringify(processorConfig);
 
@@ -403,7 +403,7 @@ function applyOverrides(fullConfig, configDir, filePath) {
 	}
 
 	if (!Array.isArray(overrides)) {
-		throw Error(
+		throw new TypeError(
 			'The `overrides` configuration property should be an array, e.g. { "overrides": [{ "files": "*.css", "rules": {} }] }.',
 		);
 	}
@@ -412,7 +412,7 @@ function applyOverrides(fullConfig, configDir, filePath) {
 		const { files, ...configOverrides } = override;
 
 		if (!files) {
-			throw Error(
+			throw new Error(
 				'Every object in the `overrides` configuration property should have a `files` property with globs, e.g. { "overrides": [{ "files": "*.css", "rules": {} }] }.',
 			);
 		}
diff --git a/lib/formatters/tapFormatter.js b/lib/formatters/tapFormatter.js
index fd05191401..f7ade9f21f 100644
--- a/lib/formatters/tapFormatter.js
+++ b/lib/formatters/tapFormatter.js
@@ -4,7 +4,7 @@
  * @type {import('stylelint').Formatter}
  */
 const tapFormatter = (results) => {
-	let lines = [`TAP version 13\n1..${results.length}`];
+	const lines = [`TAP version 13\n1..${results.length}`];
 
 	results.forEach((result, index) => {
 		lines.push(
diff --git a/lib/getPostcssResult.js b/lib/getPostcssResult.js
index 0bc5dfcd86..e02d26c128 100644
--- a/lib/getPostcssResult.js
+++ b/lib/getPostcssResult.js
@@ -46,13 +46,9 @@ module.exports = function getPostcssResult(stylelint, options = {}) {
 			}
 
 			/** @type {Syntax | null} */
-			let syntax = null;
-
-			if (options.customSyntax) {
-				syntax = getCustomSyntax(options.customSyntax);
-			} else {
-				syntax = cssSyntax(stylelint, options.filePath);
-			}
+			const syntax = options.customSyntax
+				? getCustomSyntax(options.customSyntax)
+				: cssSyntax(stylelint, options.filePath);
 
 			const postcssOptions = {
 				from: options.filePath,
diff --git a/lib/reference/keywordSets.js b/lib/reference/keywordSets.js
index dcb52f240a..3fd9df2255 100644
--- a/lib/reference/keywordSets.js
+++ b/lib/reference/keywordSets.js
@@ -683,7 +683,7 @@ keywordSets.nonStandardHtmlTags = new Set([
 function uniteSets(...args) {
 	return new Set(
 		[...args].reduce((/** @type {string[]} */ result, set) => {
-			return result.concat([...set]);
+			return [...result, ...set];
 		}, []),
 	);
 }
diff --git a/lib/reportUnknownRuleNames.js b/lib/reportUnknownRuleNames.js
index 371f4b6373..b995755bda 100644
--- a/lib/reportUnknownRuleNames.js
+++ b/lib/reportUnknownRuleNames.js
@@ -11,7 +11,7 @@ const MAX_SUGGESTIONS_COUNT = 3;
  * @return {string[]}
  */
 function extractSuggestions(ruleName) {
-	const suggestions = new Array(MAX_LEVENSHTEIN_DISTANCE);
+	const suggestions = Array.from({ length: MAX_LEVENSHTEIN_DISTANCE });
 
 	for (let i = 0; i < suggestions.length; i++) {
 		suggestions[i] = [];
diff --git a/lib/rules/block-closing-brace-newline-after/index.js b/lib/rules/block-closing-brace-newline-after/index.js
index 81472eb84f..cab53d4af2 100644
--- a/lib/rules/block-closing-brace-newline-after/index.js
+++ b/lib/rules/block-closing-brace-newline-after/index.js
@@ -112,11 +112,10 @@ const rule = (primary, secondaryOptions, context) => {
 						if (primary.startsWith('always')) {
 							const index = nodeToCheckRaws.before.search(/\r?\n/);
 
-							if (index >= 0) {
-								nodeToCheckRaws.before = nodeToCheckRaws.before.slice(index);
-							} else {
-								nodeToCheckRaws.before = context.newline + nodeToCheckRaws.before;
-							}
+							nodeToCheckRaws.before =
+								index >= 0
+									? nodeToCheckRaws.before.slice(index)
+									: context.newline + nodeToCheckRaws.before;
 
 							return;
 						}
diff --git a/lib/rules/block-closing-brace-newline-before/index.js b/lib/rules/block-closing-brace-newline-before/index.js
index 8dd6c7eeb0..ba6597c548 100644
--- a/lib/rules/block-closing-brace-newline-before/index.js
+++ b/lib/rules/block-closing-brace-newline-before/index.js
@@ -93,11 +93,10 @@ const rule = (primary, _secondaryOptions, context) => {
 							firstWhitespaceIndex >= 0 ? statementRaws.after.slice(firstWhitespaceIndex) : '';
 						const newlineIndex = newlineAfter.search(/\r?\n/);
 
-						if (newlineIndex >= 0) {
-							statementRaws.after = newlineBefore + newlineAfter.slice(newlineIndex);
-						} else {
-							statementRaws.after = newlineBefore + context.newline + newlineAfter;
-						}
+						statementRaws.after =
+							newlineIndex >= 0
+								? newlineBefore + newlineAfter.slice(newlineIndex)
+								: newlineBefore + context.newline + newlineAfter;
 
 						return;
 					}
diff --git a/lib/rules/block-opening-brace-newline-after/index.js b/lib/rules/block-opening-brace-newline-after/index.js
index 78570e465a..d5bbc5883f 100644
--- a/lib/rules/block-opening-brace-newline-after/index.js
+++ b/lib/rules/block-opening-brace-newline-after/index.js
@@ -93,11 +93,10 @@ const rule = (primary, _secondaryOptions, context) => {
 						if (primary.startsWith('always')) {
 							const index = nodeToCheckRaws.before.search(/\r?\n/);
 
-							if (index >= 0) {
-								nodeToCheckRaws.before = nodeToCheckRaws.before.slice(index);
-							} else {
-								nodeToCheckRaws.before = context.newline + nodeToCheckRaws.before;
-							}
+							nodeToCheckRaws.before =
+								index >= 0
+									? nodeToCheckRaws.before.slice(index)
+									: context.newline + nodeToCheckRaws.before;
 
 							backupCommentNextBefores.delete(nodeToCheck);
 
diff --git a/lib/rules/color-named/generateColorFuncs.js b/lib/rules/color-named/generateColorFuncs.js
index 6b8b3f5073..0a83f0a4ee 100644
--- a/lib/rules/color-named/generateColorFuncs.js
+++ b/lib/rules/color-named/generateColorFuncs.js
@@ -197,30 +197,34 @@ function generateColorFuncs(hexString) {
 	const xyz_d50 = chromaticAdaptationD65_D50(xyz_d65);
 	const lab = xyz2lab(xyz_d50);
 
-	func.push(`rgb(${rgbStr})`);
-	func.push(`rgba(${rgbStr},1)`);
-	func.push(`rgba(${rgbStr},100%)`);
-	func.push(`rgb(${rgbPercStr})`);
-	func.push(`rgba(${rgbPercStr},1)`);
-	func.push(`rgba(${rgbPercStr},100%)`);
-	func.push(`hsl(${hslStr})`);
-	func.push(`hsla(${hslStr},1)`);
-	func.push(`hsla(${hslStr},100%)`);
-	func.push(`hwb(${hwbStr})`);
-	func.push(`hwb(${hwbStr},1)`);
-	func.push(`hwb(${hwbStr},100%)`);
+	func.push(
+		`rgb(${rgbStr})`,
+		`rgba(${rgbStr},1)`,
+		`rgba(${rgbStr},100%)`,
+		`rgb(${rgbPercStr})`,
+		`rgba(${rgbPercStr},1)`,
+		`rgba(${rgbPercStr},100%)`,
+		`hsl(${hslStr})`,
+		`hsla(${hslStr},1)`,
+		`hsla(${hslStr},100%)`,
+		`hwb(${hwbStr})`,
+		`hwb(${hwbStr},1)`,
+		`hwb(${hwbStr},100%)`,
+	);
 
 	// technically, this should be 0 - but then #808080 wouldn't even be gray
 	if (lab[1] * lab[1] < 0.01 && lab[2] * lab[2] < 0.01) {
 		// yay! gray!
 		const grayStr = Math.round(lab[0]);
 
-		func.push(`gray(${grayStr})`);
-		func.push(`gray(${grayStr},1)`);
-		func.push(`gray(${grayStr},100%)`);
-		func.push(`gray(${grayStr}%)`);
-		func.push(`gray(${grayStr}%,1)`);
-		func.push(`gray(${grayStr}%,100%)`);
+		func.push(
+			`gray(${grayStr})`,
+			`gray(${grayStr},1)`,
+			`gray(${grayStr},100%)`,
+			`gray(${grayStr}%)`,
+			`gray(${grayStr}%,1)`,
+			`gray(${grayStr}%,100%)`,
+		);
 	}
 
 	return func;
diff --git a/lib/rules/declaration-block-semicolon-newline-after/index.js b/lib/rules/declaration-block-semicolon-newline-after/index.js
index a27238a3b9..b09081196d 100644
--- a/lib/rules/declaration-block-semicolon-newline-after/index.js
+++ b/lib/rules/declaration-block-semicolon-newline-after/index.js
@@ -67,11 +67,10 @@ const rule = (primary, _secondaryOptions, context) => {
 						if (primary.startsWith('always')) {
 							const index = nodeToCheck.raws.before.search(/\r?\n/);
 
-							if (index >= 0) {
-								nodeToCheck.raws.before = nodeToCheck.raws.before.slice(index);
-							} else {
-								nodeToCheck.raws.before = context.newline + nodeToCheck.raws.before;
-							}
+							nodeToCheck.raws.before =
+								index >= 0
+									? nodeToCheck.raws.before.slice(index)
+									: context.newline + nodeToCheck.raws.before;
 
 							return;
 						}
diff --git a/lib/rules/declaration-colon-newline-after/index.js b/lib/rules/declaration-colon-newline-after/index.js
index a7e555b63b..4b003e68e6 100644
--- a/lib/rules/declaration-colon-newline-after/index.js
+++ b/lib/rules/declaration-colon-newline-after/index.js
@@ -64,11 +64,9 @@ const rule = (primary, _secondaryOptions, context) => {
 							const betweenBefore = between.slice(0, sliceIndex);
 							const betweenAfter = between.slice(sliceIndex);
 
-							if (/^\s*\n/.test(betweenAfter)) {
-								decl.raws.between = betweenBefore + betweenAfter.replace(/^[^\S\r\n]*/, '');
-							} else {
-								decl.raws.between = betweenBefore + context.newline + betweenAfter;
-							}
+							decl.raws.between = /^\s*\n/.test(betweenAfter)
+								? betweenBefore + betweenAfter.replace(/^[^\S\r\n]*/, '')
+								: betweenBefore + context.newline + betweenAfter;
 
 							return;
 						}
diff --git a/lib/rules/font-family-name-quotes/__tests__/index.js b/lib/rules/font-family-name-quotes/__tests__/index.js
index b36413392b..0c137f9d60 100644
--- a/lib/rules/font-family-name-quotes/__tests__/index.js
+++ b/lib/rules/font-family-name-quotes/__tests__/index.js
@@ -29,7 +29,8 @@ testRule({
 	ruleName,
 	config: ['always-unless-keyword'],
 
-	accept: variablePositiveTests.concat([
+	accept: [
+		...variablePositiveTests,
 		{
 			code: 'a { font-family: "Lucida Grande", "Arial", sans-serif; }',
 		},
@@ -84,7 +85,7 @@ testRule({
 		{
 			code: 'a { font-family: "ሀ"; }',
 		},
-	]),
+	],
 
 	reject: [
 		{
@@ -170,7 +171,8 @@ testRule({
 	ruleName,
 	config: ['always-where-recommended'],
 
-	accept: variablePositiveTests.concat([
+	accept: [
+		...variablePositiveTests,
 		{
 			code: 'a { font: 1em "Lucida Grande", Arial, sans-serif; }',
 		},
@@ -222,7 +224,7 @@ testRule({
 		{
 			code: "a { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; }",
 		},
-	]),
+	],
 
 	reject: [
 		{
@@ -298,7 +300,8 @@ testRule({
 	ruleName,
 	config: ['always-where-required'],
 
-	accept: variablePositiveTests.concat([
+	accept: [
+		...variablePositiveTests,
 		{
 			code: 'a { font: 1em Lucida Grande, Arial, sans-serif; }',
 		},
@@ -332,7 +335,7 @@ testRule({
 		{
 			code: 'a { font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Roboto, sans-serif; }',
 		},
-	]),
+	],
 
 	reject: [
 		{
diff --git a/lib/rules/function-parentheses-newline-inside/index.js b/lib/rules/function-parentheses-newline-inside/index.js
index cbcddd14e8..c1c2179251 100644
--- a/lib/rules/function-parentheses-newline-inside/index.js
+++ b/lib/rules/function-parentheses-newline-inside/index.js
@@ -171,7 +171,7 @@ function getCheckBefore(valueNode) {
 function getCheckAfter(valueNode) {
 	let after = '';
 
-	for (const node of valueNode.nodes.slice().reverse()) {
+	for (const node of [...valueNode.nodes].reverse()) {
 		if (node.type === 'comment') {
 			continue;
 		}
@@ -250,7 +250,7 @@ function fixAfterForAlways(valueNode, newline) {
 function fixAfterForNever(valueNode) {
 	valueNode.after = '';
 
-	for (const node of valueNode.nodes.slice().reverse()) {
+	for (const node of [...valueNode.nodes].reverse()) {
 		if (node.type === 'comment') {
 			continue;
 		}
diff --git a/lib/rules/function-whitespace-after/index.js b/lib/rules/function-whitespace-after/index.js
index 44e9db2368..36219f5c44 100644
--- a/lib/rules/function-whitespace-after/index.js
+++ b/lib/rules/function-whitespace-after/index.js
@@ -92,22 +92,20 @@ const rule = (primary, _secondaryOptions, context) => {
 					result,
 					ruleName,
 				});
-			} else if (primary === 'never') {
-				if (isWhitespace(nextChar)) {
-					if (fix) {
-						fix(index);
-
-						return;
-					}
+			} else if (primary === 'never' && isWhitespace(nextChar)) {
+				if (fix) {
+					fix(index);
 
-					report({
-						message: messages.rejected,
-						node,
-						index: nodeIndex + index,
-						result,
-						ruleName,
-					});
+					return;
 				}
+
+				report({
+					message: messages.rejected,
+					node,
+					index: nodeIndex + index,
+					result,
+					ruleName,
+				});
 			}
 		}
 
diff --git a/lib/rules/max-line-length/__tests__/index.js b/lib/rules/max-line-length/__tests__/index.js
index 7538fea016..9af2664630 100644
--- a/lib/rules/max-line-length/__tests__/index.js
+++ b/lib/rules/max-line-length/__tests__/index.js
@@ -3,8 +3,9 @@
 const postcssScss = require('postcss-scss');
 
 const { messages, ruleName } = require('..');
+
 const testUrl = 'somethingsomething something\tsomething';
-const _21whitespaces = new Array(21).fill('\u0020').join('');
+const _21whitespaces = Array.from({ length: 21 }).fill('\u0020').join('');
 
 testRule({
 	ruleName,
diff --git a/lib/rules/named-grid-areas-no-invalid/utils/findNotContiguousOrRectangular.js b/lib/rules/named-grid-areas-no-invalid/utils/findNotContiguousOrRectangular.js
index b9911f84bd..b359c54133 100644
--- a/lib/rules/named-grid-areas-no-invalid/utils/findNotContiguousOrRectangular.js
+++ b/lib/rules/named-grid-areas-no-invalid/utils/findNotContiguousOrRectangular.js
@@ -46,7 +46,7 @@ function namedAreas(areas) {
 
 	names.delete('.');
 
-	return Array.from(names);
+	return [...names];
 }
 
 /**
diff --git a/lib/rules/no-duplicate-selectors/__tests__/index.js b/lib/rules/no-duplicate-selectors/__tests__/index.js
index 119135dce9..8250a6aab4 100644
--- a/lib/rules/no-duplicate-selectors/__tests__/index.js
+++ b/lib/rules/no-duplicate-selectors/__tests__/index.js
@@ -5,6 +5,7 @@ const postcss = require('postcss');
 const postcssImport = require('postcss-import');
 
 const rule = require('..');
+
 const { messages, ruleName } = rule;
 
 testRule({
diff --git a/lib/rules/no-duplicate-selectors/index.js b/lib/rules/no-duplicate-selectors/index.js
index b6e51a341c..6aacf596b7 100644
--- a/lib/rules/no-duplicate-selectors/index.js
+++ b/lib/rules/no-duplicate-selectors/index.js
@@ -67,7 +67,7 @@ function rule(actual, options) {
 
 			// Sort the selectors list so that the order of the constituents
 			// doesn't matter
-			const sortedSelectorList = normalizedSelectorList.slice().sort().join(',');
+			const sortedSelectorList = [...normalizedSelectorList].sort().join(',');
 
 			const selectorLine = ruleNode.source.start.line;
 
diff --git a/lib/rules/no-extra-semicolons/index.js b/lib/rules/no-extra-semicolons/index.js
index 3bff6eb47e..52de368c18 100644
--- a/lib/rules/no-extra-semicolons/index.js
+++ b/lib/rules/no-extra-semicolons/index.js
@@ -82,12 +82,12 @@ function rule(actual, options, context) {
 				return;
 			}
 
-			let rawBeforeNode = node.raws.before;
+			const rawBeforeNode = node.raws.before;
 
 			if (rawBeforeNode && rawBeforeNode.trim().length !== 0) {
-				let allowedSemi = 0;
+				const allowedSemi = 0;
 
-				let rawBeforeIndexStart = 0;
+				const rawBeforeIndexStart = 0;
 
 				const fixSemiIndices = [];
 
@@ -151,7 +151,7 @@ function rule(actual, options, context) {
 			const rawOwnSemicolon = node.raws.ownSemicolon;
 
 			if (rawOwnSemicolon) {
-				let allowedSemi = 0;
+				const allowedSemi = 0;
 
 				const fixSemiIndices = [];
 
diff --git a/lib/rules/no-invalid-position-at-import-rule/index.js b/lib/rules/no-invalid-position-at-import-rule/index.js
index df4d84acb2..819e252326 100644
--- a/lib/rules/no-invalid-position-at-import-rule/index.js
+++ b/lib/rules/no-invalid-position-at-import-rule/index.js
@@ -53,15 +53,13 @@ function rule(actual, options) {
 				return;
 			}
 
-			if (node.type === 'atrule' && nodeName === 'import') {
-				if (invalidPosition) {
-					report({
-						message: messages.rejected,
-						node,
-						result,
-						ruleName,
-					});
-				}
+			if (node.type === 'atrule' && nodeName === 'import' && invalidPosition) {
+				report({
+					message: messages.rejected,
+					node,
+					result,
+					ruleName,
+				});
 			}
 		});
 	};
diff --git a/lib/rules/selector-attribute-name-disallowed-list/index.js b/lib/rules/selector-attribute-name-disallowed-list/index.js
index c89ac0fd3a..09ba062071 100644
--- a/lib/rules/selector-attribute-name-disallowed-list/index.js
+++ b/lib/rules/selector-attribute-name-disallowed-list/index.js
@@ -17,7 +17,7 @@ const messages = ruleMessages(ruleName, {
 });
 
 function rule(listInput) {
-	const list = [].concat(listInput);
+	const list = [listInput].flat();
 
 	return (root, result) => {
 		const validOptions = validateOptions(result, ruleName, {
diff --git a/lib/rules/selector-attribute-operator-allowed-list/index.js b/lib/rules/selector-attribute-operator-allowed-list/index.js
index 8818dd2f85..0437cba1a3 100644
--- a/lib/rules/selector-attribute-operator-allowed-list/index.js
+++ b/lib/rules/selector-attribute-operator-allowed-list/index.js
@@ -16,7 +16,7 @@ const messages = ruleMessages(ruleName, {
 });
 
 function rule(listInput) {
-	const list = [].concat(listInput);
+	const list = [listInput].flat();
 
 	return (root, result) => {
 		const validOptions = validateOptions(result, ruleName, {
diff --git a/lib/rules/selector-attribute-operator-disallowed-list/index.js b/lib/rules/selector-attribute-operator-disallowed-list/index.js
index c8c14182ec..b7ecc88e20 100644
--- a/lib/rules/selector-attribute-operator-disallowed-list/index.js
+++ b/lib/rules/selector-attribute-operator-disallowed-list/index.js
@@ -16,7 +16,7 @@ const messages = ruleMessages(ruleName, {
 });
 
 function rule(listInput) {
-	const list = [].concat(listInput);
+	const list = [listInput].flat();
 
 	return (root, result) => {
 		const validOptions = validateOptions(result, ruleName, {
diff --git a/lib/rules/selector-disallowed-list/index.js b/lib/rules/selector-disallowed-list/index.js
index afbc09fb87..b95769b10b 100644
--- a/lib/rules/selector-disallowed-list/index.js
+++ b/lib/rules/selector-disallowed-list/index.js
@@ -16,7 +16,7 @@ const messages = ruleMessages(ruleName, {
 });
 
 function rule(listInput) {
-	const list = [].concat(listInput);
+	const list = [listInput].flat();
 
 	return (root, result) => {
 		const validOptions = validateOptions(result, ruleName, {
diff --git a/lib/rules/selector-list-comma-newline-after/__tests__/index.js b/lib/rules/selector-list-comma-newline-after/__tests__/index.js
index ee5681a89c..3691e9c975 100644
--- a/lib/rules/selector-list-comma-newline-after/__tests__/index.js
+++ b/lib/rules/selector-list-comma-newline-after/__tests__/index.js
@@ -187,11 +187,13 @@ testRule({
 			code: 'a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z {\n}',
 			fixed:
 				'a,\nb,\nc,\nd,\ne,\nf,\ng,\nh,\ni,\nj,\nk,\nl,\nm,\nn,\no,\np,\nq,\nr,\ns,\nt,\nu,\nv,\nw,\nx,\ny,\nz {\n}',
-			warnings: new Array(25).fill(0).map((_, i) => ({
-				message: messages.expectedAfter(),
-				line: 1,
-				column: 2 * (i + 1),
-			})),
+			warnings: Array.from({ length: 25 })
+				.fill(0)
+				.map((_, i) => ({
+					message: messages.expectedAfter(),
+					line: 1,
+					column: 2 * (i + 1),
+				})),
 		},
 	],
 });
@@ -329,11 +331,13 @@ testRule({
 		{
 			code: 'a,\nb,\nc,\nd,\ne,\nf,\ng,\nh,\ni,\nj,\nk,\nl,\nm,\nn,\no,\np,\nq,\nr,\ns,\nt,\nu,\nv,\nw,\nx,\ny,\nz {\n}',
 			fixed: 'a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z {\n}',
-			warnings: new Array(25).fill(0).map((_, i) => ({
-				message: messages.rejectedAfterMultiLine(),
-				line: 1 + i,
-				column: 2,
-			})),
+			warnings: Array.from({ length: 25 })
+				.fill(0)
+				.map((_, i) => ({
+					message: messages.rejectedAfterMultiLine(),
+					line: 1 + i,
+					column: 2,
+				})),
 		},
 	],
 });
diff --git a/lib/rules/string-quotes/index.js b/lib/rules/string-quotes/index.js
index 9fafe76463..77dc710766 100644
--- a/lib/rules/string-quotes/index.js
+++ b/lib/rules/string-quotes/index.js
@@ -82,28 +82,26 @@ function rule(expectation, secondary, context) {
 						return;
 					}
 
-					if (attributeNode.quoteMark === correctQuote) {
-						if (avoidEscape) {
-							const needsCorrectEscape = attributeNode.value.includes(correctQuote);
-							const needsOtherEscape = attributeNode.value.includes(erroneousQuote);
+					if (attributeNode.quoteMark === correctQuote && avoidEscape) {
+						const needsCorrectEscape = attributeNode.value.includes(correctQuote);
+						const needsOtherEscape = attributeNode.value.includes(erroneousQuote);
 
-							if (needsOtherEscape) {
-								return;
-							}
+						if (needsOtherEscape) {
+							return;
+						}
 
-							if (needsCorrectEscape) {
-								if (context.fix) {
-									selectorFixed = true;
-									attributeNode.quoteMark = erroneousQuote;
-								} else {
-									report({
-										message: messages.expected(expectation === 'single' ? 'double' : expectation),
-										node: ruleNode,
-										index: attributeNode.sourceIndex + attributeNode.offsetOf('value'),
-										result,
-										ruleName,
-									});
-								}
+						if (needsCorrectEscape) {
+							if (context.fix) {
+								selectorFixed = true;
+								attributeNode.quoteMark = erroneousQuote;
+							} else {
+								report({
+									message: messages.expected(expectation === 'single' ? 'double' : expectation),
+									node: ruleNode,
+									index: attributeNode.sourceIndex + attributeNode.offsetOf('value'),
+									result,
+									ruleName,
+								});
 							}
 						}
 					}
diff --git a/lib/rules/unit-allowed-list/index.js b/lib/rules/unit-allowed-list/index.js
index 2a3b53e4e3..a71d4fda75 100644
--- a/lib/rules/unit-allowed-list/index.js
+++ b/lib/rules/unit-allowed-list/index.js
@@ -20,7 +20,7 @@ const messages = ruleMessages(ruleName, {
 });
 
 function rule(listInput, options) {
-	const list = [].concat(listInput);
+	const list = [listInput].flat();
 
 	return (root, result) => {
 		const validOptions = validateOptions(
diff --git a/lib/rules/unit-disallowed-list/index.js b/lib/rules/unit-disallowed-list/index.js
index 6bfec7142b..4c09e01230 100644
--- a/lib/rules/unit-disallowed-list/index.js
+++ b/lib/rules/unit-disallowed-list/index.js
@@ -29,7 +29,7 @@ const getMediaFeatureName = (mediaFeatureNode) => {
 };
 
 function rule(listInput, options) {
-	const list = [].concat(listInput);
+	const list = [listInput].flat();
 
 	return (root, result) => {
 		const validOptions = validateOptions(
diff --git a/lib/standalone.js b/lib/standalone.js
index 0e9e01950c..d1963305cd 100644
--- a/lib/standalone.js
+++ b/lib/standalone.js
@@ -18,6 +18,7 @@ const path = require('path');
 const pkg = require('../package.json');
 const prepareReturnValue = require('./prepareReturnValue');
 const { default: ignore } = require('ignore');
+
 const DEFAULT_IGNORE_FILENAME = '.stylelintignore';
 const ALWAYS_IGNORED_GLOBS = ['**/node_modules/**'];
 const writeFileAtomic = require('write-file-atomic');
@@ -157,13 +158,9 @@ module.exports = function (options) {
 					!postcssResult.stylelint.ignored &&
 					!postcssResult.stylelint.ruleDisableFix
 				) {
-					if (!postcssResult.stylelint.disableWritingFix) {
-						// If we're fixing, the output should be the fixed code
-						returnValue.output = postcssResult.root.toString(postcssResult.opts.syntax);
-					} else {
-						// If the writing of the fix is disabled, the input code is returned as-is
-						returnValue.output = code;
-					}
+					returnValue.output = !postcssResult.stylelint.disableWritingFix
+						? postcssResult.root.toString(postcssResult.opts.syntax)
+						: code;
 				}
 
 				return returnValue;
diff --git a/lib/utils/__tests__/isNonNegativeInteger.test.js b/lib/utils/__tests__/isNonNegativeInteger.test.js
index 23a2cfc761..933e0a0dd1 100644
--- a/lib/utils/__tests__/isNonNegativeInteger.test.js
+++ b/lib/utils/__tests__/isNonNegativeInteger.test.js
@@ -12,7 +12,7 @@ describe('isNonNegativeInteger', () => {
 		expect(isNonNegativeInteger(-1)).toBe(false);
 		expect(isNonNegativeInteger(-0.1)).toBe(false);
 		expect(isNonNegativeInteger(0.1)).toBe(false);
-		expect(isNonNegativeInteger(NaN)).toBe(false);
+		expect(isNonNegativeInteger(Number.NaN)).toBe(false);
 	});
 
 	it('returns false for a non-number', () => {
diff --git a/lib/utils/addEmptyLineBefore.js b/lib/utils/addEmptyLineBefore.js
index a2d3db4f46..68a53891f4 100644
--- a/lib/utils/addEmptyLineBefore.js
+++ b/lib/utils/addEmptyLineBefore.js
@@ -15,11 +15,9 @@ module.exports = function addEmptyLineBefore(node, newline) {
 		return node;
 	}
 
-	if (!/\r?\n/.test(raws.before)) {
-		raws.before = newline.repeat(2) + raws.before;
-	} else {
-		raws.before = raws.before.replace(/(\r?\n)/, `${newline}$1`);
-	}
+	raws.before = !/\r?\n/.test(raws.before)
+		? newline.repeat(2) + raws.before
+		: raws.before.replace(/(\r?\n)/, `${newline}$1`);
 
 	return node;
 };
diff --git a/lib/utils/whitespaceChecker.js b/lib/utils/whitespaceChecker.js
index b8bd464c4e..47edff9b77 100644
--- a/lib/utils/whitespaceChecker.js
+++ b/lib/utils/whitespaceChecker.js
@@ -219,10 +219,12 @@ module.exports = function whitespaceChecker(targetWhitespace, expectation, messa
 			return;
 		}
 
-		if (targetWhitespace === 'space' && oneCharBefore === ' ') {
-			if (activeArgs.onlyOneChar || !isWhitespace(twoCharsBefore)) {
-				return;
-			}
+		if (
+			targetWhitespace === 'space' &&
+			oneCharBefore === ' ' &&
+			(activeArgs.onlyOneChar || !isWhitespace(twoCharsBefore))
+		) {
+			return;
 		}
 
 		assertFunction(messageFunc);
@@ -289,24 +291,26 @@ module.exports = function whitespaceChecker(targetWhitespace, expectation, messa
 
 		if (targetWhitespace === 'newline') {
 			// If index is followed by a Windows CR-LF ...
-			if (oneCharAfter === '\r' && twoCharsAfter === '\n') {
-				if (activeArgs.onlyOneChar || !isWhitespace(source[index + 3])) {
-					return;
-				}
+			if (
+				oneCharAfter === '\r' &&
+				twoCharsAfter === '\n' &&
+				(activeArgs.onlyOneChar || !isWhitespace(source[index + 3]))
+			) {
+				return;
 			}
 
 			// If index is followed by a Unix LF ...
-			if (oneCharAfter === '\n') {
-				if (activeArgs.onlyOneChar || !isWhitespace(twoCharsAfter)) {
-					return;
-				}
+			if (oneCharAfter === '\n' && (activeArgs.onlyOneChar || !isWhitespace(twoCharsAfter))) {
+				return;
 			}
 		}
 
-		if (targetWhitespace === 'space' && oneCharAfter === ' ') {
-			if (activeArgs.onlyOneChar || !isWhitespace(twoCharsAfter)) {
-				return;
-			}
+		if (
+			targetWhitespace === 'space' &&
+			oneCharAfter === ' ' &&
+			(activeArgs.onlyOneChar || !isWhitespace(twoCharsAfter))
+		) {
+			return;
 		}
 
 		assertFunction(messageFunc);
@@ -347,6 +351,6 @@ function isValue(x) {
  */
 function assertFunction(x) {
 	if (typeof x !== 'function') {
-		throw new Error(`\`${x}\` must be a function`);
+		throw new TypeError(`\`${x}\` must be a function`);
 	}
 }