Cache pending promises (#12)

index.js

@@ -40,15 +40,11 @@ module.exports = (fn, opts) => {
 			});
 		};
 
+		setData(key, ret);
+
 		if (isPromise(ret) && opts.cachePromiseRejection === false) {
-			// Only cache resolved promises unless `cachePromiseRejection` is set to `true`
-			ret
-				.then(() => {
-					setData(key, ret);
-				})
-				.catch(() => {});
-		} else {
-			setData(key, ret);
+			// Remove rejected promises from cache unless `cachePromiseRejection` is set to `true`
+			ret.catch(() => cache.delete(key));
 		}
 
 		return ret;

readme.md

@@ -104,7 +104,7 @@ You could for example change it to only cache on the first argument `x => JSON.s
 Type: `Object`<br>
 Default: `new Map()`
 
-Use a different cache storage. Must implement the following methods: `.has(key)`, `.get(key)`, `.set(key, value)`, and optionally `.clear()`. You could for example use a `WeakMap` instead or [`quick-lru`](https://github.com/sindresorhus/quick-lru) for a LRU cache.
+Use a different cache storage. Must implement the following methods: `.has(key)`, `.get(key)`, `.set(key, value)`, `.delete(key)`, and optionally `.clear()`. You could for example use a `WeakMap` instead or [`quick-lru`](https://github.com/sindresorhus/quick-lru) for a LRU cache.
 
 ##### cachePromiseRejection
 

test.js

@@ -87,8 +87,14 @@ test('do not cache rejected promises', async t => {
 	});
 
 	await t.throws(memoized(), 'foo bar');
-	t.is(await memoized(), 2);
-	t.is(await memoized(), 2);
+
+	const first = memoized();
+	const second = memoized();
+	const third = memoized();
+
+	t.is(await first, 2);
+	t.is(await second, 2);
+	t.is(await third, 2);
 });
 
 test('cache rejected promises if enabled', async t => {