feat: rework the module.

Now only undefined rejection is treated as 'empty value' and replaced with Error instance.

Fixed types as requested in #9 & #15 not return type is inferred from promise.

BREAKING CHANGE: now module has default export only.

src/index.ts

@@ -1,17 +1,15 @@
-export type AWAIT_OF_RETURN_TYPE = [any?, Error?];
+type AwaitOfReturnType<T> = Readonly<[T | undefined, Error?]>;
 
-export function of(promise: Promise<any>): Promise<AWAIT_OF_RETURN_TYPE> {
+export default function of<T = any>(promise: Promise<T>): Promise<AwaitOfReturnType<T>> {
   return Promise.resolve(promise)
-    .then((r: any): AWAIT_OF_RETURN_TYPE => [r])
+    .then((result): Readonly<[T]> => [result])
     .catch(
-      (e: Error | undefined | null): AWAIT_OF_RETURN_TYPE => {
-        if (e === undefined || e === null) {
-          return [e, new Error('Rejection with empty value')];
+      (err): Readonly<[undefined, Error]> => {
+        if (typeof err === 'undefined') {
+          err = new Error('Rejection with empty value');
         }
 
-        return [undefined, e];
+        return [undefined, err];
       },
     );
 }
-
-export default of;

tests/index.spec.ts

@@ -1,5 +1,5 @@
 /* eslint-disable @typescript-eslint/no-non-null-assertion,@typescript-eslint/ban-ts-ignore */
-import { of } from '../src';
+import of from '../src';
 
 describe('await-of', () => {
   it('should return resolve result as first array`s item', async () => {
@@ -18,7 +18,7 @@ describe('await-of', () => {
   });
 
   it('should return unhandled error as second array`s item', async () => {
-    const [res, err = undefined] = await of(
+    const [res, err] = await of(
       new Promise(() => {
         throw new Error('Unhandled error!');
       }),