[firestore][js] First pass of javascript implementation

lib/utils/index.js

@@ -5,6 +5,7 @@ import { Platform } from 'react-native';
 
 // modeled after base64 web-safe chars, but ordered by ASCII
 const PUSH_CHARS = '-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz';
+const AUTO_ID_CHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
 const hasOwnProperty = Object.hasOwnProperty;
 const DEFAULT_CHUNK_SIZE = 50;
 
@@ -373,3 +374,16 @@ export function promiseOrCallback(promise: Promise, optionalCallback?: Function)
     return Promise.reject(error);
   });
 }
+
+/**
+ * Generate a firestore auto id for use with collection/document .add()
+ * @return {string}
+ */
+export function firestoreAutoId(): string {
+  let autoId = '';
+
+  for (let i = 0; i < 20; i++) {
+    autoId += AUTO_ID_CHARS.charAt(Math.floor(Math.random() * AUTO_ID_CHARS.length));
+  }
+  return autoId;
+}