Fix operator precedence

sindresorhus · May 20, 2020 · c890378 · c890378
1 parent d610645
commit c890378
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Showing 2 changed files with 47 additions and 7 deletions.
diff --git a/rules/prefer-array-find.js b/rules/prefer-array-find.js
@@ -87,17 +87,22 @@ const destructuringAssignmentSelector = [
 // - `ObjectPattern`: `[{foo = baz}] = array.filter(bar)`
 const assignmentNeedParenthesize = ({type}) => type === 'ObjectExpression' || type === 'ObjectPattern';
 
-// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#Operator_precedence
-// Higher than `??` and `||`
-const hasHigherPrecedence = (node, operator) => (
+// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table
+const hasLowerPrecedence = (node, operator) => (
 	(node.type === 'LogicalExpression' && (
 		node.operator === operator ||
-		// `??` has lower precedence than `||`
-		// https://tc39.es/proposal-nullish-coalescing/
-		(operator === '??' && node.operator === '||')
+		// https://tc39.es/proposal-nullish-coalescing/ says
+    // `??` has lower precedence than `||`
+		// But MDN says
+    // `??` has higher precedence than `||`
+		(operator === '||' && node.operator === '??') ||
+		(operator === '??' && (node.operator === '||' || node.operator === '&&'))
 	)) ||
 	node.type === 'ConditionalExpression' ||
+	// Lower than `assignment`, should already parenthesized
+	/* istanbul ignore next */
 	node.type === 'AssignmentExpression' ||
+	node.type === 'YieldExpression' ||
 	node.type === 'SequenceExpression'
 );
 
@@ -128,7 +133,7 @@ const fixDestructuring = (source, node) => {
 		const defaultValue = element.right;
 		let defaultValueText = source.getText(defaultValue);
 
-		if (isParenthesized(defaultValue, source) || hasHigherPrecedence(defaultValue, operator)) {
+		if (isParenthesized(defaultValue, source) || hasLowerPrecedence(defaultValue, operator)) {
 			defaultValueText = `(${defaultValueText})`;
 		}
 

diff --git a/test/prefer-array-find.js b/test/prefer-array-find.js
@@ -312,6 +312,24 @@ ruleTester.run('prefer-array-find', rule, {
 				]
 			}]
 		},
+		// // TODO:  enable this test when ESLint support `nullish coalescing operator`
+		// {
+		// 	code: 'const [foo = a ?? b] = array.filter(bar)',
+		// 	output: 'const [foo = a ?? b] = array.filter(bar)',
+		// 	errors: [{
+		// 		messageId: MESSAGE_ID_DESTRUCTURING_DECLARATION,
+		// 		suggestions: [
+		// 			{
+		// 				messageId: MESSAGE_ID_USE_NULLISH_COALESCING_OPERATOR,
+		// 				output: 'const foo = array.find(bar) ?? (a ?? b)'
+		// 			},
+		// 			{
+		// 				messageId: MESSAGE_ID_USE_LOGICAL_OR_OPERATOR,
+		// 				output: 'const foo = array.find(bar) || (a ?? b)'
+		// 			}
+		// 		]
+		// 	}]
+		// },
 		{
 			code: 'const [foo = a || b] = array.filter(bar)',
 			output: 'const [foo = a || b] = array.filter(bar)',
@@ -328,6 +346,23 @@ ruleTester.run('prefer-array-find', rule, {
 					}
 				]
 			}]
+		},
+		{
+			code: 'const [foo = a && b] = array.filter(bar)',
+			output: 'const [foo = a && b] = array.filter(bar)',
+			errors: [{
+				messageId: MESSAGE_ID_DESTRUCTURING_DECLARATION,
+				suggestions: [
+					{
+						messageId: MESSAGE_ID_USE_NULLISH_COALESCING_OPERATOR,
+						output: 'const foo = array.find(bar) ?? (a && b)'
+					},
+					{
+						messageId: MESSAGE_ID_USE_LOGICAL_OR_OPERATOR,
+						output: 'const foo = array.find(bar) || a && b'
+					}
+				]
+			}]
 		}
 	]
 });