[firestore][js] First pass of javascript implementation

lib/modules/firestore/QuerySnapshot.js

@@ -0,0 +1,66 @@
+/**
+ * @flow
+ * QuerySnapshot representation wrapper
+ */
+import DocumentChange from './DocumentChange';
+import DocumentSnapshot from './DocumentSnapshot';
+import Query from './Query';
+
+import type { DocumentChangeNativeData } from './DocumentChange';
+import type { DocumentSnapshotNativeData } from './DocumentSnapshot';
+
+type QuerySnapshotNativeData = {
+  changes: DocumentChangeNativeData[],
+  documents: DocumentSnapshotNativeData[],
+  readTime: string,
+}
+
+ /**
+ * @class QuerySnapshot
+ */
+export default class QuerySnapshot {
+  _changes: DocumentChange[];
+  _docs: DocumentSnapshot[];
+  _query: Query;
+  _readTime: string;
+
+  constructor(firestore: Object, query: Query, nativeData: QuerySnapshotNativeData) {
+    this._changes = nativeData.changes.map(change => new DocumentChange(change));
+    this._docs = nativeData.documents.map(doc => new DocumentSnapshot(firestore, doc));
+    this._query = query;
+    this._readTime = nativeData.readTime;
+  }
+
+  get docChanges(): DocumentChange[] {
+    return this._changes;
+  }
+
+  get docs(): DocumentSnapshot[] {
+    return this._docs;
+  }
+
+  get empty(): boolean {
+    return this._docs.length === 0;
+  }
+
+  get query(): Query {
+    return this._query;
+  }
+
+  get readTime(): string {
+    return this._readTime;
+  }
+
+  get size(): number {
+    return this._docs.length;
+  }
+
+  forEach(callback: DocumentSnapshot => any) {
+    // TODO: Validation
+    // validate.isFunction('callback', callback);
+
+    for (const doc of this.docs) {
+      callback(doc);
+    }
+  }
+}