feat(firestore): implement the getDoc modular api

Author: dhenneke

packages/firestore/lib/modular/query.d.ts

@@ -239,6 +239,42 @@ export function startAfter<AppModelType, DbModelType extends DocumentData>(
  */
 export function limit(limit: number): QueryLimitConstraint;
 
+/**
+ * Reads the document referred to by this `DocumentReference`.
+ *
+ * Note: `getDoc()` attempts to provide up-to-date data when possible by waiting
+ * for data from the server, but it may return cached data or fail if you are
+ * offline and the server cannot be reached. To specify this behavior, invoke
+ * {@link getDocFromCache} or {@link getDocFromServer}.
+ *
+ * @param reference - The reference of the document to fetch.
+ * @returns A Promise resolved with a `DocumentSnapshot` containing the
+ * current document contents.
+ */
+export declare function getDoc<T>(reference: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
+
+/**
+ * Reads the document referred to by this `DocumentReference` from cache.
+ * Returns an error if the document is not currently cached.
+ *
+ * @returns A `Promise` resolved with a `DocumentSnapshot` containing the
+ * current document contents.
+ */
+export declare function getDocFromCache<T>(
+  reference: DocumentReference<T>,
+): Promise<DocumentSnapshot<T>>;
+
+/**
+ * Reads the document referred to by this `DocumentReference` from the server.
+ * Returns an error if the network is not available.
+ *
+ * @returns A `Promise` resolved with a `DocumentSnapshot` containing the
+ * current document contents.
+ */
+export declare function getDocFromServer<T>(
+  reference: DocumentReference<T>,
+): Promise<DocumentSnapshot<T>>;
+
 /**
  * Executes the query and returns the results as a `QuerySnapshot`.
  *

packages/firestore/lib/modular/query.js

@@ -169,6 +169,30 @@ export function limitToLast(limit) {
   return new QueryConstraint('limitToLast', limit);
 }
 
+/**
+ * @param {DocumentReference} query
+ * @returns {Promise<DocumentSnapshot>}
+ */
+export function getDoc(reference) {
+  return reference.get({ source: 'default' });
+}
+
+/**
+ * @param {DocumentReference} query
+ * @returns {Promise<DocumentSnapshot>}
+ */
+export function getDocFromCache(reference) {
+  return reference.get({ source: 'cache' });
+}
+
+/**
+ * @param {DocumentReference} query
+ * @returns {Promise<DocumentSnapshot>}
+ */
+export function getDocFromServer(reference) {
+  return reference.get({ source: 'server' });
+}
+
 /**
  * @param {Query} query
  * @returns {Promise<QuerySnapshot>}