Refactor web3Wrapper to a separate package

1 files changed, 24 insertions, 0 deletions

diff --git a/packages/utils/src/promisify.ts b/packages/utils/src/promisify.ts
new file mode 100644
index 000000000..c114cf32f
--- /dev/null
+++ b/packages/utils/src/promisify.ts
@@ -0,0 +1,24 @@
+import * as _ from 'lodash';
+
+/**
+ * Transforms callback-based function -- func(arg1, arg2 .. argN, callback) -- into an ES6-compatible Promise.
+ * Promisify provides a default callback of the form (error, result) and rejects when `error` is not null. You can also
+ * supply thisArg object as the second argument which will be passed to `apply`.
+ */
+export function promisify<T>(
+    originalFn: (
+        ...args: any[],
+        // HACK: This can't be properly typed without variadic kinds https://github.com/Microsoft/TypeScript/issues/5453
+    ) => void,
+    thisArg?: any,
+): (...callArgs: any[]) => Promise<T> {
+    const promisifiedFunction = async (...callArgs: any[]): Promise<T> => {
+        return new Promise<T>((resolve, reject) => {
+            const callback = (err: Error|null, data?: T) => {
+                _.isNull(err) ? resolve(data) : reject(err);
+            };
+            originalFn.apply(thisArg, [...callArgs, callback]);
+        });
+    };
+    return promisifiedFunction;
+}