chore(typescript): ship to TypeScript

src/util/assert.ts

@@ -0,0 +1,8 @@
+import { AssertionError } from './error'
+
+export default function (predicate: any, message: string) {
+  if (!predicate) {
+    message = message || `expect ${predicate} to be true`
+    throw new AssertionError(message)
+  }
+}