fixed guard issue with undefined argument

LCcodder · Nov 3, 2024 · 9ae0968 · 9ae0968
1 parent b62350d
commit 9ae0968
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Showing 2 changed files with 5 additions and 1 deletion.
diff --git a/src/functions/predicatesAndTyping.ts b/src/functions/predicatesAndTyping.ts
@@ -35,7 +35,7 @@ export function generateConditionalGuard<T>(callback: (entity: T) => boolean):
 export function generateGuard<T>(prop: keyof T, propPrimitive: string | symbol): 
 (checkingVariable: unknown) => checkingVariable is T {
     return (checkingVariable: unknown): checkingVariable is T => {
-        return typeof (checkingVariable as Required<T>)[prop as keyof T] === propPrimitive;
+        return Boolean(checkingVariable) && typeof (checkingVariable as Required<T>)[prop as keyof T] === propPrimitive;
     }
 }
 

diff --git a/tests/functions/predicatesAndTyping.test.ts b/tests/functions/predicatesAndTyping.test.ts
@@ -67,6 +67,10 @@ describe("generateGuard function", () => {
         expect(guard(testUser)).toEqual(false)
     })
 
+    test("Testing for guard failure (with undefined)", () => {
+        expect(guard(undefined)).toEqual(false)
+    })
+
     test("Testing for guard success", () => {
         const testUser = {
             id: 123,