🛡️ Better safeguarding in the type predicate.

Author: adam-rocska

src/task-queue-descriptor.ts

@@ -16,9 +16,10 @@ export const TaskQueueDescriptor = <I, O>(
 ) => descriptor;
 
 export const isTaskQueueDescriptor = (
-  value: object
-): value is TaskQueueDescriptor<unknown, unknown> => {
-  const candidate = value as TaskQueueDescriptor<unknown, unknown>;
+  candidate: any
+): candidate is TaskQueueDescriptor<unknown, unknown> => {
+  if (typeof candidate !== "object") return false;
+  if (candidate === null) return false;
   if (typeof candidate.name !== 'string') return false;
   if (!isCodec(candidate.codec)) return false;
   if (typeof candidate.task !== 'function') return false;

test/unit/task-queue-descriptor.test.ts

@@ -16,6 +16,19 @@ describe('TaskQueueDescriptor', () => {
   });
 
   describe('.isTaskQueueDescriptor()', () => {
+    it.each([
+      [1],
+      [true],
+      [false],
+      [null],
+      [undefined],
+      [{}],
+      [[]],
+      [() => {}],
+    ])("should return false if the candidate is not a non-null object", candidate => {
+      expect(isTaskQueueDescriptor(candidate)).toBe(false);
+    });
+
     it('should return true if the value is a TaskQueueDescriptor', () => {
       buildStubRecords({
         name: ['test'],