From d3fb2f3c20df2e258a27ba6efe1ab997f6568c03 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Joost=20Z=C3=B6llner?= <github@joost.io>
Date: Wed, 3 Oct 2018 00:17:15 +0200
Subject: [PATCH] Fix #437: Add undefined check before using toLowerCase (#507)

---
 src/reactA11yImageButtonHasAltRule.ts            |  1 +
 src/tests/ReactA11yImageButtonHasAltRuleTests.ts | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/src/reactA11yImageButtonHasAltRule.ts b/src/reactA11yImageButtonHasAltRule.ts
index c5c9ff978..412834ac2 100644
--- a/src/reactA11yImageButtonHasAltRule.ts
+++ b/src/reactA11yImageButtonHasAltRule.ts
@@ -59,6 +59,7 @@ class ReactA11yImageButtonHasAltWalker extends Lint.RuleWalker {
         if (!typeAttribute
             || typeAttribute.initializer === undefined
             || !isStringLiteral(typeAttribute.initializer)
+            || getStringLiteral(typeAttribute) === undefined
             || getStringLiteral(typeAttribute)!.toLowerCase() !== 'image') {
             return;
         }
diff --git a/src/tests/ReactA11yImageButtonHasAltRuleTests.ts b/src/tests/ReactA11yImageButtonHasAltRuleTests.ts
index ba6c83360..d6a4b6678 100644
--- a/src/tests/ReactA11yImageButtonHasAltRuleTests.ts
+++ b/src/tests/ReactA11yImageButtonHasAltRuleTests.ts
@@ -37,6 +37,16 @@ describe('reactA11yImageButtonHasAlt', (): void => {
 
             TestHelper.assertNoViolation(ruleName, script);
         });
+
+        it("when input element has an expression for its type thats undefined.", (): void => {
+            const script: string = `
+                import React = require('react');
+                const type = undefined;
+                const a = <input type={type} />;
+            `;
+
+            TestHelper.assertNoViolation(ruleName, script);
+        });
     });
 
     describe('should fail', (): void => {