Run prefer-nullish-coalescing on codebase

docs/rules/prefer-nullish-coalescing.md

@@ -0,0 +1,27 @@
+# Prefer the nullish coalescing operator(`??`) over the logical OR operator(`||`)
+
+The [nullish coalescing operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator) only coalesces when the value is `null` or `undefined`, it is safer than [logical OR operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_OR)  which coalesces on any [falsy value](https://developer.mozilla.org/en-US/docs/Glossary/Falsy).
+
+## Fail
+
+```js
+const foo = bar || value;
+```
+
+```js
+foo ||= value;
+```
+
+```js
+if (foo || value) {}
+```
+
+## Pass
+
+```js
+const foo = bar ?? value;
+```
+
+```js
+foo ??= value;
+```

index.js

@@ -102,6 +102,8 @@ module.exports = {
 				'unicorn/prefer-module': 'error',
 				'unicorn/prefer-negative-index': 'error',
 				'unicorn/prefer-node-protocol': 'error',
+				// TODO: Enable this by default when targeting Node.js 14.
+				'unicorn/prefer-nullish-coalescing': 'off',
 				'unicorn/prefer-number-properties': 'error',
 				// TODO: Enable this by default when targeting a Node.js version that supports `Object.hasOwn`.
 				'unicorn/prefer-object-has-own': 'off',

readme.md

@@ -98,6 +98,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-module": "error",
 			"unicorn/prefer-negative-index": "error",
 			"unicorn/prefer-node-protocol": "error",
+			"unicorn/prefer-nullish-coalescing": "off",
 			"unicorn/prefer-number-properties": "error",
 			"unicorn/prefer-object-has-own": "off",
 			"unicorn/prefer-optional-catch-binding": "error",
@@ -202,6 +203,7 @@ Each rule has emojis denoting:
 | [prefer-module](docs/rules/prefer-module.md) | Prefer JavaScript modules (ESM) over CommonJS. | ✅ | 🔧 | 💡 |
 | [prefer-negative-index](docs/rules/prefer-negative-index.md) | Prefer negative index over `.length - index` for `{String,Array,TypedArray}#slice()`, `Array#splice()` and `Array#at()`. | ✅ | 🔧 |  |
 | [prefer-node-protocol](docs/rules/prefer-node-protocol.md) | Prefer using the `node:` protocol when importing Node.js builtin modules. | ✅ | 🔧 |  |
+| [prefer-nullish-coalescing](docs/rules/prefer-nullish-coalescing.md) | Prefer the nullish coalescing operator(`??`) over the logical OR operator(`||`). |  |  | 💡 |
 | [prefer-number-properties](docs/rules/prefer-number-properties.md) | Prefer `Number` static properties over global ones. | ✅ | 🔧 | 💡 |
 | [prefer-object-has-own](docs/rules/prefer-object-has-own.md) | Prefer `Object.hasOwn(…)` over `Object.prototype.hasOwnProperty.call(…)`. |  | 🔧 |  |
 | [prefer-optional-catch-binding](docs/rules/prefer-optional-catch-binding.md) | Prefer omitting the `catch` binding parameter. | ✅ | 🔧 |  |

rules/better-regex.js

@@ -15,7 +15,7 @@ const newRegExp = [
 ].join('');
 
 const create = context => {
-	const {sortCharacterClasses} = context.options[0] || {};
+	const {sortCharacterClasses} = context.options[0] ?? {};
 
 	const ignoreList = [];
 

rules/custom-error-definition.js

@@ -133,7 +133,7 @@ function * customErrorDefinition(context, node) {
 					yield fixer.insertTextAfterRange([
 						superExpression.range[0],
 						superExpression.range[0] + 6
-					], rhs.raw || rhs.name);
+					], rhs.raw ?? rhs.name);
 				}
 
 				yield fixer.removeRange([

rules/expiring-todo-comments.js

@@ -87,7 +87,7 @@ function parseTodoWithArguments(string, {terms}) {
 function createArgumentGroup(arguments_) {
 	const groups = {};
 	for (const {value, type} of arguments_) {
-		groups[type] = groups[type] || [];
+		groups[type] = groups[type] ?? [];
 		groups[type].push(value);
 	}
 
@@ -226,7 +226,7 @@ function tryToCoerceVersion(rawVersion) {
 	try {
 		// Try to semver.parse a perfect match while semver.coerce tries to fix errors
 		// But coerce can't parse pre-releases.
-		return semver.parse(version) || semver.coerce(version);
+		return semver.parse(version) ?? semver.coerce(version);
 	} catch {
 		/* istanbul ignore next: We don't have this `package.json` to test */
 		return false;
@@ -420,7 +420,7 @@ const create = context => {
 			}
 		}
 
-		const packageEngines = packageJson.engines || {};
+		const packageEngines = packageJson.engines ?? {};
 
 		for (const engine of engines) {
 			uses++;

rules/filename-case.js

@@ -98,7 +98,7 @@ function fixFilename(words, caseFunctions, {leading, extension}) {
 
 const leadingUnderscoresRegex = /^(?<leading>_+)(?<tailing>.*)$/;
 function splitFilename(filename) {
-	const result = leadingUnderscoresRegex.exec(filename) || {groups: {}};
+	const result = leadingUnderscoresRegex.exec(filename) ?? {groups: {}};
 	const {leading = '', tailing = filename} = result.groups;
 
 	const words = [];
@@ -143,9 +143,9 @@ function englishishJoinWords(words) {
 }
 
 const create = context => {
-	const options = context.options[0] || {};
+	const options = context.options[0] ?? {};
 	const chosenCases = getChosenCases(options);
-	const ignore = (options.ignore || []).map(item => {
+	const ignore = (options.ignore ?? []).map(item => {
 		if (item instanceof RegExp) {
 			return item;
 		}

rules/fix/remove-argument.js

@@ -6,8 +6,8 @@ function removeArgument(fixer, node, sourceCode) {
 	const callExpression = node.parent;
 	const index = callExpression.arguments.indexOf(node);
 	const parentheses = getParentheses(node, sourceCode);
-	const firstToken = parentheses[0] || node;
-	const lastToken = parentheses[parentheses.length - 1] || node;
+	const firstToken = parentheses[0] ?? node;
+	const lastToken = parentheses[parentheses.length - 1] ?? node;
 
 	let [start] = firstToken.range;
 	let [, end] = lastToken.range;

rules/import-index.js

@@ -21,7 +21,7 @@ const importIndex = (context, node, argument) => {
 };
 
 const create = context => {
-	const options = context.options[0] || {};
+	const options = context.options[0] ?? {};
 
 	const rules = {
 		[STATIC_REQUIRE_SELECTOR]: node => importIndex(context, node, node.arguments[0])

rules/no-array-push-push.js

@@ -21,7 +21,7 @@ const selector = `${arrayPushExpressionStatement} + ${arrayPushExpressionStateme
 
 function getFirstExpression(node, sourceCode) {
 	const {parent} = node;
-	const visitorKeys = sourceCode.visitorKeys[parent.type] || Object.keys(parent);
+	const visitorKeys = sourceCode.visitorKeys[parent.type] ?? Object.keys(parent);
 
 	for (const property of visitorKeys) {
 		const value = parent[property];

rules/no-for-loop.js

@@ -255,7 +255,7 @@ const isIndexVariableAssignedToInTheLoopBody = (indexVariable, bodyScope) => {
 const someVariablesLeakOutOfTheLoop = (forStatement, variables, forScope) => {
 	return variables.some(variable => {
 		return !variable.references.every(reference => {
-			return scopeContains(forScope, reference.from) ||
+			return scopeContains(forScope, reference.from) ??
 				nodeContains(forStatement, reference.identifier);
 		});
 	});
@@ -354,8 +354,8 @@ const create = context => {
 					const shouldGenerateIndex = isIndexVariableUsedElsewhereInTheLoopBody(indexVariable, bodyScope, arrayIdentifierName);
 
 					const index = indexIdentifierName;
-					const element = elementIdentifierName ||
-						avoidCapture(singular(arrayIdentifierName) || defaultElementName, getChildScopesRecursive(bodyScope), context.parserOptions.ecmaVersion);
+					const element = elementIdentifierName ??
+						avoidCapture(singular(arrayIdentifierName) ?? defaultElementName, getChildScopesRecursive(bodyScope), context.parserOptions.ecmaVersion);
 					const array = arrayIdentifierName;
 
 					let declarationElement = element;

rules/no-keyword-prefix.js

@@ -11,7 +11,7 @@ const prepareOptions = ({
 	onlyCamelCase = true
 } = {}) => {
 	return {
-		disallowedPrefixes: (disallowedPrefixes || [
+		disallowedPrefixes: (disallowedPrefixes ?? [
 			'new',
 			'class'
 		]),

rules/no-unused-properties.js

@@ -6,7 +6,7 @@ const messages = {
 };
 
 const getDeclaratorOrPropertyValue = declaratorOrProperty =>
-	declaratorOrProperty.init ||
+	declaratorOrProperty.init ??
 	declaratorOrProperty.value;
 
 const isMemberExpressionCall = memberExpression =>

rules/prefer-add-event-listener.js

@@ -61,8 +61,8 @@ const isClearing = node => {
 };
 
 const create = context => {
-	const options = context.options[0] || {};
-	const excludedPackages = new Set(options.excludedPackages || ['koa', 'sax']);
+	const options = context.options[0] ?? {};
+	const excludedPackages = new Set(options.excludedPackages ?? ['koa', 'sax']);
 	let isDisabled;
 
 	const nodeReturnsSomething = new WeakMap();
@@ -95,7 +95,7 @@ const create = context => {
 		},
 
 		ReturnStatement(node) {
-			codePathInfo.returnsSomething = codePathInfo.returnsSomething || Boolean(node.argument);
+			codePathInfo.returnsSomething = codePathInfo.returnsSomething ?? Boolean(node.argument);
 		},
 
 		'AssignmentExpression:exit'(node) {

rules/prefer-keyboard-event-key.js

@@ -84,7 +84,7 @@ const fix = node => fixer => {
 	const isTestingEquality = operator === '==' || operator === '===';
 	const isRightValid = isTestingEquality && right.type === 'Literal' && typeof right.value === 'number';
 	// Either a meta key or a printable character
-	const keyCode = translateToKey[right.value] || String.fromCharCode(right.value);
+	const keyCode = translateToKey[right.value] ?? String.fromCharCode(right.value);
 	// And if we recognize the `.keyCode`
 	if (!isRightValid || !keyCode) {
 		return;

rules/prefer-nullish-coalescing.js

@@ -0,0 +1,74 @@
+'use strict';
+const {getStaticValue} = require('eslint-utils');
+const {matches} = require('./selectors/index.js');
+const {isBooleanNode} = require('./utils/boolean.js');
+
+const ERROR = 'error';
+const SUGGESTION = 'suggestion';
+const messages = {
+	[ERROR]: 'Prefer `{{replacement}}` over `{{original}}`.',
+	[SUGGESTION]: 'Use `{{replacement}}`'
+};
+
+const selector = matches([
+	'LogicalExpression[operator="||"]',
+	'AssignmentExpression[operator="||="]'
+]);
+
+/** @param {import('eslint').Rule.RuleContext} context */
+const create = context => {
+	return {
+		[selector](node) {
+			if (
+				[node.parent, node.left, node.right].some(node => node.type === 'LogicalExpression') ||
+				isBooleanNode(node) ||
+				isBooleanNode(node.left)
+			) {
+				return;
+			}
+
+			const {left} = node;
+
+			const staticValue = getStaticValue(left, context.getScope());
+			if (staticValue) {
+				const {value} = staticValue;
+				if (!(typeof value === 'undefined' || value === null)) {
+					return;
+				}
+			}
+
+			const isAssignment = node.type === 'AssignmentExpression';
+			const originalOperator = isAssignment ? '||=' : '||';
+			const replacementOperator = isAssignment ? '??=' : '??';
+			const operatorToken = context.getSourceCode()
+				.getTokenAfter(
+					node.left,
+					token => token.type === 'Punctuator' && token.value === originalOperator
+				);
+
+			const messageData = {
+				original: originalOperator,
+				replacement: replacementOperator
+			};
+			return {
+				node: operatorToken,
+				messageId: ERROR,
+				data: messageData,
+				fix: fixer => fixer.replaceText(operatorToken, replacementOperator)
+			};
+		}
+	};
+};
+
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description: 'Prefer the nullish coalescing operator(`??`) over the logical OR operator(`||`).'
+		},
+		messages,
+		hasSuggestions: true,
+		fixable: 'code'
+	}
+};

rules/prefer-reflect-apply.js

@@ -68,7 +68,7 @@ const create = context => {
 	return {
 		[selector]: node => {
 			const sourceCode = context.getSourceCode();
-			const fix = fixDirectApplyCall(node, sourceCode) || fixFunctionPrototypeCall(node, sourceCode);
+			const fix = fixDirectApplyCall(node, sourceCode) ?? fixFunctionPrototypeCall(node, sourceCode);
 			if (fix) {
 				return {
 					node,

rules/prefer-spread.js

@@ -134,7 +134,7 @@ function fixConcat(node, sourceCode, fixableArguments) {
 					text = `...${text}`;
 				}
 
-				return text || ' ';
+				return text ?? ' ';
 			})
 			.join(', ');
 
@@ -388,7 +388,7 @@ const create = context => {
 					fix: fixConcat(
 						node,
 						sourceCode,
-						node.arguments.map(node => getConcatArgumentSpreadable(node, scope) || {node, isSpreadable: true})
+						node.arguments.map(node => getConcatArgumentSpreadable(node, scope) ?? {node, isSpreadable: true})
 					)
 				});
 			}

rules/prefer-string-slice.js

@@ -37,7 +37,7 @@ const isLengthProperty = node => (
 	node.property.name === 'length'
 );
 
-const isLikelyNumeric = node => isLiteralNumber(node) || isLengthProperty(node);
+const isLikelyNumeric = node => isLiteralNumber(node) ?? isLengthProperty(node);
 
 const create = context => {
 	const sourceCode = context.getSourceCode();

rules/prefer-switch.js

@@ -33,7 +33,7 @@ function getEqualityComparisons(node) {
 
 function getCommonReferences(expressions, candidates) {
 	for (const {left, right} of expressions) {
-		candidates = candidates.filter(node => isSame(node, left) || isSame(node, right));
+		candidates = candidates.filter(node => isSame(node, left) ?? isSame(node, right));
 
 		if (candidates.length === 0) {
 			break;

rules/utils/avoid-capture.js

@@ -26,7 +26,7 @@ const nameCollidesWithArgumentsSpecial = (name, scopes, isStrict) => {
 		return false;
 	}
 
-	return isStrict || scopes.some(scope => scopeHasArgumentsSpecial(scope));
+	return isStrict ?? scopes.some(scope => scopeHasArgumentsSpecial(scope));
 };
 
 /*
@@ -47,7 +47,7 @@ function unicorn() {
 ```
 */
 const isUnresolvedName = (name, scopes) => scopes.some(scope =>
-	scope.references.some(reference => reference.identifier && reference.identifier.name === name && !reference.resolved) ||
+	scope.references.some(reference => reference.identifier && reference.identifier.name === name && !reference.resolved) ??
 	isUnresolvedName(name, scope.childScopes)
 );