typescript-eslint · BeauRussell · Dec 15, 2025 · Dec 15, 2025 · Dec 15, 2025
diff --git a/packages/eslint-plugin/src/rules/prefer-optional-chain-utils/analyzeChain.ts b/packages/eslint-plugin/src/rules/prefer-optional-chain-utils/analyzeChain.ts
@@ -467,6 +467,52 @@ function getReportDescriptor(
   const fix: ReportFixFunction = fixer =>
     fixer.replaceTextRange(reportRange, newCode);
 
+  // #11840: Don't suggest optional-chain + strict-null when OR-chain has undefined check
+  if (
+    node.type === AST_NODE_TYPES.LogicalExpression &&
+    node.operator === '||' &&
+    parts.some(part => part.optional) &&
+    lastOperand.node.type === AST_NODE_TYPES.BinaryExpression &&
+    (lastOperand.node.operator === '===' ||
+      lastOperand.node.operator === '!==') &&
+    ((lastOperand.node.left.type === AST_NODE_TYPES.Literal &&
+      lastOperand.node.left.value == null) ||
+      (lastOperand.node.right.type === AST_NODE_TYPES.Literal &&
+        lastOperand.node.right.value == null))
+  ) {
+    // Check if any part of the OR-chain is "x === undefined" or "x !== undefined"
+    const checkForUndefined = (expr: TSESTree.Node): boolean => {
+      if (
+        expr.type === AST_NODE_TYPES.BinaryExpression &&
+        (expr.operator === '===' || expr.operator === '!==')
+      ) {
+        return (
+          (expr.left.type === AST_NODE_TYPES.Identifier &&
+            expr.left.name === 'undefined') ||
+          (expr.right.type === AST_NODE_TYPES.Identifier &&
+            expr.right.name === 'undefined')
+        );
+      }
+      if (
+        expr.type === AST_NODE_TYPES.LogicalExpression &&
+        expr.operator === '||'
+      ) {
+        return checkForUndefined(expr.left) || checkForUndefined(expr.right);
+      }
+      return false;
+    };
+
+    if (checkForUndefined(node)) {
+      return {
+        loc: {
+          end: sourceCode.getLocFromIndex(reportRange[1]),
+          start: sourceCode.getLocFromIndex(reportRange[0]),
+        },
+        messageId: 'preferOptionalChain',
+      };
+    }
+  }
+
   return {
     loc: {
       end: sourceCode.getLocFromIndex(reportRange[1]),

diff --git a/packages/eslint-plugin/tests/rules/prefer-optional-chain/prefer-optional-chain.test.ts b/packages/eslint-plugin/tests/rules/prefer-optional-chain/prefer-optional-chain.test.ts
@@ -1338,6 +1338,44 @@ describe('chain ending with comparison', () => {
         errors: [{ messageId: 'preferOptionalChain', suggestions: null }],
         output: `undefined !== foo?.bar?.baz;`,
       },
+      {
+        // https://github.com/typescript-eslint/typescript-eslint/issues/11840
+        code: `
+          declare const foo: { bar: number | null } | undefined;
+          if (foo === undefined || foo.bar === null) {
+          }
+        `,
+        errors: [
+          {
+            messageId: 'preferOptionalChain',
+            suggestions: [], // This should not offer suggestions as it's not a true error
+          },
+        ],
+      },
+      {
+        code: `
+          declare const foo: { bar: number | null } | undefined;
+          if (foo.bar === null || foo === undefined) {
+          }
+        `,
+        errors: [{ messageId: 'preferOptionalChain', suggestions: [] }],
+      },
+      {
+        code: `
+          declare const foo: { bar: number | null } | undefined;
+          if (undefined === foo || null === foo.bar) {
+          }
+        `,
+        errors: [{ messageId: 'preferOptionalChain', suggestions: [] }],
+      },
+      {
+        code: `
+          declare const foo: { bar: { baz: number | null } } | undefined;
+          if (foo === undefined || foo.bar.baz === null) {
+          }
+        `,
+        errors: [{ messageId: 'preferOptionalChain', suggestions: [] }],
+      },
     ],
     valid: [
       'foo && foo.bar == undeclaredVar;',