5 files changed, 40 insertions, 1 deletions
diff --git a/packages/order-watcher/CHANGELOG.json b/packages/order-watcher/CHANGELOG.json
index ce56e492c..feebb9d69 100644
--- a/packages/order-watcher/CHANGELOG.json
+++ b/packages/order-watcher/CHANGELOG.json
@@ -1,5 +1,14 @@
 [
     {
+        "version": "2.1.2",
+        "changes": [
+            {
+                "note": "Added getStats function and returns a Stats object",
+                "pr": 1118
+            }
+        ]
+    },
+    {
         "version": "2.1.1",
         "changes": [
             {
diff --git a/packages/order-watcher/src/index.ts b/packages/order-watcher/src/index.ts
index d2f91eab1..8280c73a4 100644
--- a/packages/order-watcher/src/index.ts
+++ b/packages/order-watcher/src/index.ts
@@ -7,6 +7,7 @@ export {
     OrderState,
     ExchangeContractErrs,
     OrderRelevantState,
+    Stats,
 } from '@0xproject/types';
 
 export { OnOrderStateChangeCallback, OrderWatcherConfig } from './types';
diff --git a/packages/order-watcher/src/order_watcher/order_watcher.ts b/packages/order-watcher/src/order_watcher/order_watcher.ts
index f9a63efe3..eb37bd617 100644
--- a/packages/order-watcher/src/order_watcher/order_watcher.ts
+++ b/packages/order-watcher/src/order_watcher/order_watcher.ts
@@ -30,7 +30,7 @@ import {
     orderHashUtils,
     OrderStateUtils,
 } from '@0xproject/order-utils';
-import { AssetProxyId, ExchangeContractErrs, OrderState, SignedOrder } from '@0xproject/types';
+import { AssetProxyId, ExchangeContractErrs, OrderState, SignedOrder, Stats } from '@0xproject/types';
 import { errorUtils, intervalUtils } from '@0xproject/utils';
 import { BlockParamLiteral, LogEntryEvent, LogWithDecodedArgs, Provider } from 'ethereum-types';
 import * as _ from 'lodash';
@@ -213,6 +213,14 @@ export class OrderWatcher {
         this._expirationWatcher.unsubscribe();
         intervalUtils.clearAsyncExcludingInterval(this._cleanupJobIntervalIdIfExists);
     }
+    /**
+     * Gets statistics of the OrderWatcher Instance.
+     */
+    public getStats(): Stats {
+        return {
+            orderCount: _.size(this._orderByOrderHash),
+        };
+    }
     private async _cleanupAsync(): Promise<void> {
         for (const orderHash of _.keys(this._orderByOrderHash)) {
             this._cleanupOrderRelatedState(orderHash);
diff --git a/packages/order-watcher/test/order_watcher_test.ts b/packages/order-watcher/test/order_watcher_test.ts
index 60d9069e8..4545f84bf 100644
--- a/packages/order-watcher/test/order_watcher_test.ts
+++ b/packages/order-watcher/test/order_watcher_test.ts
@@ -140,6 +140,23 @@ describe('OrderWatcher', () => {
             expect(() => orderWatcher.subscribe(_.noop.bind(_))).to.throw(OrderWatcherError.SubscriptionAlreadyPresent);
         });
     });
+    describe('#getStats', async () => {
+        it('orderCount should increment and decrement with order additions and removals', async () => {
+            signedOrder = await fillScenarios.createFillableSignedOrderAsync(
+                makerAssetData,
+                takerAssetData,
+                makerAddress,
+                takerAddress,
+                fillableAmount,
+            );
+            const orderHash = orderHashUtils.getOrderHashHex(signedOrder);
+            expect(orderWatcher.getStats().orderCount).to.be.eq(0);
+            await orderWatcher.addOrderAsync(signedOrder);
+            expect(orderWatcher.getStats().orderCount).to.be.eq(1);
+            orderWatcher.removeOrder(orderHash);
+            expect(orderWatcher.getStats().orderCount).to.be.eq(0);
+        });
+    });
     describe('tests with cleanup', async () => {
         afterEach(async () => {
             orderWatcher.unsubscribe();
diff --git a/packages/types/src/index.ts b/packages/types/src/index.ts
index 6bc966ba1..d33048b61 100644
--- a/packages/types/src/index.ts
+++ b/packages/types/src/index.ts
@@ -620,3 +620,7 @@ export interface EIP712TypedData {
     message: EIP712Object;
     primaryType: string;
 }
+
+export interface Stats {
+    orderCount: number;
+}