feat: add safeAwait func

Author: chandq

src/async.ts

@@ -59,3 +59,35 @@ export function asyncMap<T, R>(
     }
   });
 }
+
+/**
+ * Execute a promise safely
+ *
+ * @param { Promise } promise
+ * @param { Object= } errorExt - Additional Information you can pass to the err object
+ * @return { Promise }
+ * @example
+ * async function asyncTaskWithCb(cb) {
+     let err, user, savedTask, notification;
+
+     [ err, user ] = await to(UserModel.findById(1));
+     if(!user) return cb('No user found');
+
+     [ err, savedTask ] = await to(TaskModel({userId: user.id, name: 'Demo Task'}));
+     if(err) return cb('Error occurred while saving task')
+
+    cb(null, savedTask);
+}
+ */
+export function safeAwait<T, U = Error>(promise: Promise<T>, errorExt?: object): Promise<[U, undefined] | [null, T]> {
+  return promise
+    .then<[null, T]>((data: T) => [null, data])
+    .catch<[U, undefined]>((err: U) => {
+      if (errorExt) {
+        const parsedError = Object.assign({}, err, errorExt);
+        return [parsedError, undefined];
+      }
+
+      return [err, undefined];
+    });
+}

test/async.test.ts

@@ -1,4 +1,4 @@
-import { asyncMap, wait } from '../src/async';
+import { asyncMap, safeAwait, wait } from '../src/async';
 
 test('wait', () => {
   return new Promise(done => {
@@ -40,3 +40,46 @@ test('asyncMap 并发', async () => {
   );
   expect(fn).toBeCalled();
 });
+
+describe('Await safeAwait test', () => {
+  test('should return a value when resolved', async () => {
+    const testInput = 41;
+    const promise = Promise.resolve(testInput);
+
+    const [err, data] = await safeAwait<number>(promise);
+
+    expect(err).toBeNull();
+    expect(data).toEqual(testInput);
+  });
+
+  test('should return an error when promise is rejected', async () => {
+    const testInput = 41;
+    const promise = Promise.reject('Error');
+
+    const [err, data] = await safeAwait<number>(promise);
+
+    expect(err).toEqual('Error');
+    expect(data).toBeUndefined();
+  });
+
+  test('should add external properties safeAwait the error object', async () => {
+    const promise = Promise.reject({ error: 'Error message' });
+
+    const [err] = await safeAwait<string, { error: string; extraKey: number }>(promise, {
+      extraKey: 1
+    });
+
+    expect(err).toBeTruthy();
+    expect((err as any).extraKey).toEqual(1);
+    expect((err as any).error).toEqual('Error message');
+  });
+
+  test('should receive the type of the parent if no type was passed', async () => {
+    let user: { name: string };
+    let err: Error;
+    // @ts-ignore
+    [err, user] = await safeAwait(Promise.resolve({ name: '123' }));// eslint-disable-line
+
+    expect(user.name).toEqual('123');
+  });
+});