Add JS sample for calling YT Analytics API (v2)

javascript/yt_analytics_v2.html

@@ -0,0 +1,35 @@
+<script src="https://apis.google.com/js/api.js"></script>
+<script>
+  function authenticate() {
+    return gapi.auth2.getAuthInstance()
+        .signIn({scope: "https://www.googleapis.com/auth/yt-analytics.readonly"})
+        .then(function() { console.log("Sign-in successful"); },
+              function(err) { console.error("Error signing in", err); });
+  }
+  function loadClient() {
+    return gapi.client.load("https://youtubeanalytics.googleapis.com/$discovery/rest?version=v2")
+        .then(function() { console.log("GAPI client loaded for API"); },
+              function(err) { console.error("Error loading GAPI client for API", err); });
+  }
+  // Make sure the client is loaded and sign-in is complete before calling this method.
+  function execute() {
+    return gapi.client.youtubeAnalytics.reports.query({
+      "ids": "channel==MINE",
+      "startDate": "2017-01-01",
+      "endDate": "2017-12-31",
+      "metrics": "views,estimatedMinutesWatched,averageViewDuration,averageViewPercentage,subscribersGained",
+      "dimensions": "day",
+      "sort": "day"
+    })
+        .then(function(response) {
+                // Handle the results here (response.result has the parsed body).
+                console.log("Response", response);
+              },
+              function(err) { console.error("Execute error", err); });
+  }
+  gapi.load("client:auth2", function() {
+    gapi.auth2.init({client_id: 'YOUR_CLIENT_ID'});
+  });
+</script>
+<button onclick="authenticate().then(loadClient)">authorize and load</button>
+<button onclick="execute()">execute</button>