refactor: add getBaseType

src/test/utils/get_base_type.test.ts

@@ -0,0 +1,50 @@
+import { Newable } from '@inversifyjs/common';
+import { expect } from 'chai';
+
+import { getBaseType } from '../../utils/get_base_type';
+
+describe(getBaseType.name, () => {
+  describe('having a type with base type', () => {
+    let baseTypeFixture: Newable;
+    let typeFixture: Newable;
+
+    before(() => {
+      class BaseType {}
+
+      baseTypeFixture = BaseType;
+      typeFixture = class extends BaseType {};
+    });
+
+    describe('when called', () => {
+      let result: unknown;
+
+      before(() => {
+        result = getBaseType(typeFixture);
+      });
+
+      it('should return base type', () => {
+        expect(result).to.eq(baseTypeFixture);
+      });
+    });
+  });
+
+  describe('having a type with no base type', () => {
+    let typeFixture: Newable;
+
+    before(() => {
+      typeFixture = Object;
+    });
+
+    describe('when called', () => {
+      let result: unknown;
+
+      before(() => {
+        result = getBaseType(typeFixture);
+      });
+
+      it('should return undefined', () => {
+        expect(result).to.eq(undefined);
+      });
+    });
+  });
+});

src/utils/get_base_type.ts

@@ -0,0 +1,16 @@
+import { Newable } from '@inversifyjs/common';
+
+interface Prototype {
+  constructor: Newable;
+}
+
+// eslint-disable-next-line @typescript-eslint/no-unsafe-function-type
+export function getBaseType(type: Function): Newable | undefined {
+  const prototype: Prototype | null = Object.getPrototypeOf(
+    type.prototype,
+  ) as Prototype | null;
+
+  const baseType: Newable | undefined = prototype?.constructor;
+
+  return baseType;
+}