Add activeCount and pendingCount properties to the limited functi…

…on (#9)

index.js

@@ -35,5 +35,15 @@ module.exports = concurrency => {
 		}
 	};
 
-	return (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
+	const generator = (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
+	Object.defineProperties(generator, {
+		activeCount: {
+			get: () => activeCount
+		},
+		pendingCount: {
+			get: () => queue.length
+		}
+	});
+
+	return generator;
 };

readme.md

@@ -60,6 +60,13 @@ Any arguments to pass through to `fn`.
 
 Support for passing arguments on to the `fn` is provided in order to be able to avoid creating unnecessary closures. You probably don't need this optimization unless you're pushing a *lot* of functions.
 
+### limit.activeCount
+
+The number of promises that are currently running.
+
+### limit.pendingCount
+
+The number of promises that are waiting to run (i.e. their internal `fn` was not called yet).
 
 ## FAQ
 

test.js

@@ -87,3 +87,32 @@ test('does not ignore errors', async t => {
 
 	await t.throwsAsync(Promise.all(promises), {is: error});
 });
+
+test('activeCount and pendingCount properties', async t => {
+	const limit = m(5);
+	t.is(limit.activeCount, 0);
+	t.is(limit.pendingCount, 0);
+
+	const runningPromise1 = limit(() => delay(1000));
+	t.is(limit.activeCount, 1);
+	t.is(limit.pendingCount, 0);
+
+	await runningPromise1;
+	t.is(limit.activeCount, 0);
+	t.is(limit.pendingCount, 0);
+
+	const immediatePromises = Array.from({length: 5}, () => limit(() => delay(1000)));
+	const delayedPromises = Array.from({length: 3}, () => limit(() => delay(1000)));
+
+	t.is(limit.activeCount, 5);
+	t.is(limit.pendingCount, 3);
+
+	await Promise.all(immediatePromises);
+	t.is(limit.activeCount, 3);
+	t.is(limit.pendingCount, 0);
+
+	await Promise.all(delayedPromises);
+
+	t.is(limit.activeCount, 0);
+	t.is(limit.pendingCount, 0);
+});