Add initial interface of an OrderWatcher

src/mempool/order_watcher.ts

@@ -0,0 +1,27 @@
+import * as Web3 from 'web3';
+import * as _ from 'lodash';
+import {Web3Provider, SignedOrder} from '../types';
+import {Web3Wrapper} from '../web3_wrapper';
+
+export class OrderWatcher {
+    constructor(provider: Web3Provider) {
+        if (_.isUndefined((provider as any).sendAsync)) {
+            // Web3@1.0 provider doesn't support synchronous http requests,
+            // so it only has an async `send` method, instead of a `send` and `sendAsync` in web3@0.x.x`
+            // We re-assign the send method so that Web3@1.0 providers work with 0x.js
+            (provider as any).sendAsync = (provider as any).send;
+        }
+    }
+    public addOrder(signedOrder: SignedOrder): void {
+        //
+    }
+    public removeOrder(signedOrder: SignedOrder): void {
+        //
+    }
+    public subscribe(callback: OnOrderFillabilityStateChangeCallback): void {
+        //
+    }
+    public unsubscribe(): void {
+        //
+    }
+}