feat(leabderboard): Leaderboard#count()

close #560

Author: leeyeh

src/leaderboard.js

@@ -259,6 +259,25 @@ _.extend(
         authOptions,
       }).then(data => this._finishFetch(data));
     },
+    /**
+     * Counts the number of users participated in this leaderboard
+     * @param {Object} [options]
+     * @param {number} [options.version] Specify the version of the leaderboard
+     * @param {AuthOptions} [authOptions]
+     * @return {Promise<number>}
+     */
+    count({ version } = {}, authOptions) {
+      return request({
+        method: 'GET',
+        path: `/leaderboard/leaderboards/${this.statisticName}/ranks`,
+        query: {
+          count: 1,
+          limit: 0,
+          version,
+        },
+        authOptions,
+      }).then(({ count }) => count);
+    },
     _getResults(
       { skip, limit, selectUserKeys, includeStatistics, version },
       authOptions,

storage.d.ts

@@ -931,6 +931,12 @@ export class Leaderboard {
   ): Promise<void>;
 
   fetch(authOptions?: AuthOptions): Promise<Leaderboard>;
+  count(
+    options?: {
+      version?: number;
+    },
+    authOptions?: AuthOptions
+  ): Promise<Number>;
   getResults(
     options?: {
       skip?: number;

test/leaderboard.js

@@ -143,6 +143,10 @@ describe('Leaderboard', () => {
         score.version.should.eql(0);
       }));
 
+    it('count', function() {
+      return this.leaderboard.count().then(count => count.should.be.eql(4));
+    });
+
     it('getResults', function() {
       const leaderboard = this.leaderboard;
       return leaderboard