[Feature] Handle async onRetry

README.md

@@ -46,7 +46,8 @@ retry(retrier : Function, opts : Object) => Promise
   * `maxTimeout`: The maximum number of milliseconds between two retries. Default is `Infinity`.
   * `randomize`: Randomizes the timeouts by multiplying with a factor between `1` to `2`. Default is `false`.
   * `onRetry`: an optional `Function` that is invoked after a new retry is performed. It's passed the `Error` that triggered it as a parameter.
-
+  * `awaitOnRetry`: An optional flag to wait for `onRetry` to resolve before retrying.
+
 ## Authors
 
 - Guillermo Rauch ([@rauchg](https://twitter.com/rauchg)) - [ZEIT](https://zeit.co)

lib/index.js

@@ -21,7 +21,18 @@ function retry(fn, opts) {
         return;
       }
 
-      if (!op.retry(err)) {
+      if (
+        options.awaitOnRetry &&
+        options.onRetry &&
+        err &&
+        num <= options.retries
+      ) {
+        Promise.resolve(options.onRetry(err, num)).then(() => {
+          if (!op.retry(err)) {
+            reject(op.mainError());
+          }
+        });
+      } else if (!op.retry(err)) {
         reject(op.mainError());
       } else if (options.onRetry) {
         options.onRetry(err, num);

now.json

@@ -1,3 +1,3 @@
 {
-  "type": "static"
+  "version": 2
 }

test/index.js

@@ -116,16 +116,31 @@ test('with number of retries', async t => {
   try {
     await retry(() => fetch('https://www.fakewikipedia.org'), {
       retries: 2,
-      onRetry: (err, i) => {
-        if (err) {
-          // eslint-disable-next-line no-console
-          console.log('Retry error : ', err);
-        }
-
+      onRetry: (_, i) => {
         retries = i;
       }
     });
   } catch (err) {
     t.deepEqual(retries, 2);
   }
 });
+
+test('wait for async onRetry', async t => {
+  const timeout = 1000;
+  let before;
+  let after;
+
+  try {
+    await retry(() => fetch('https://www.fakewikipedia.org'), {
+      retries: 2,
+      awaitOnRetry: true,
+      onRetry: async () => {
+        before = Date.now();
+        await sleep(timeout);
+        after = Date.now();
+      }
+    });
+  } catch (err) {
+    t.is(after - before >= timeout, true);
+  }
+});