1 files changed, 44 insertions, 0 deletions
diff --git a/src/utils/event_utils.ts b/src/utils/event_utils.ts
new file mode 100644
index 000000000..07418cbc4
--- /dev/null
+++ b/src/utils/event_utils.ts
@@ -0,0 +1,44 @@
+import * as _ from 'lodash';
+import * as Web3 from 'web3';
+import {EventCallback, ContractEventArg, ContractEvent, ContractEventObj, ContractEventEmitter} from '../types';
+import * as BigNumber from 'bignumber.js';
+import promisify = require('es6-promisify');
+
+export const eventUtils = {
+    wrapEventEmitter(event: ContractEventObj): ContractEventEmitter {
+        const watch = (eventCallback: EventCallback) => {
+            const bignumberWrappingEventCallback = eventUtils._getBigNumberWrappingEventCallback(eventCallback);
+            event.watch(bignumberWrappingEventCallback);
+        };
+        const zeroExEvent = {
+            watch,
+            stopWatchingAsync: async () => {
+                await promisify(event.stopWatching, event)();
+            },
+        };
+        return zeroExEvent;
+    },
+    /**
+     * Wraps eventCallback function so that all the BigNumber arguments are wrapped in a newer version of BigNumber.
+     * @param eventCallback     Event callback function to be wrapped
+     * @return Wrapped event callback function
+     */
+    _getBigNumberWrappingEventCallback(eventCallback: EventCallback): EventCallback {
+        const bignumberWrappingEventCallback = (err: Error, event: ContractEvent) => {
+            if (_.isNull(err)) {
+                const wrapIfBigNumber = (value: ContractEventArg): ContractEventArg => {
+                    // HACK: The old version of BigNumber used by Web3@0.19.0 does not support the `isBigNumber`
+                    // and checking for a BigNumber instance using `instanceof` does not work either. We therefore
+                    // compare the constructor functions of the possible BigNumber instance and the BigNumber used by
+                    // Web3.
+                    const web3BigNumber = (Web3.prototype as any).BigNumber;
+                    const isWeb3BigNumber = web3BigNumber.toString() === value.constructor.toString();
+                    return isWeb3BigNumber ?  new BigNumber(value) : value;
+                };
+                event.args = _.mapValues(event.args, wrapIfBigNumber);
+            }
+            eventCallback(err, event);
+        };
+        return bignumberWrappingEventCallback;
+    },
+};