Replace "Export All" button for "Export Page"

Spotify limits paginations of playlist objects to a maximum of 50 items.
Depending on how many playlists a user has, multiple calls are
required, and Spotify frequently returns "Too many request" errors for
relatively small count of requests.

This commit replaces the "Export all" button with a "Export page" button
in a attempt to force a single request to be made and avoid back pressure
from Spotify.

To be clear, whats being done here is replacing the inconvenience of not
being able to download multiple playlists simultaneously due to quota
limits with the inconvenience of manually having to click a button to
download playlists in batches a total of playlist_count / 50 times.

exportify.js

@@ -40,7 +40,7 @@ window.Helpers = {
         alert(jqXHR.responseText);
       }
     })
-  }
+  },
 }
 
 var PlaylistTable = React.createClass({
@@ -49,7 +49,7 @@ var PlaylistTable = React.createClass({
       playlists: [],
       playlistCount: 0,
       nextURL: null,
-      prevURL: null
+      prevURL: null,
     };
   },
 
@@ -68,7 +68,7 @@ var PlaylistTable = React.createClass({
             this.props.access_token
           ),
           window.Helpers.apiCall(
-            "https://api.spotify.com/v1/users/" + userId + "/playlists",
+            "https://api.spotify.com/v1/users/" + userId + "/playlists?limit=50",
             this.props.access_token
           )
         ])
@@ -91,6 +91,7 @@ var PlaylistTable = React.createClass({
         this.setState({
           playlists: playlists,
           playlistCount: response.total,
+          playlistOffset: response.offset,
           nextURL: response.next,
           prevURL: response.previous
         });
@@ -102,7 +103,7 @@ var PlaylistTable = React.createClass({
   },
 
   exportPlaylists: function() {
-    PlaylistsExporter.export(this.props.access_token, this.state.playlistCount);
+    PlaylistsExporter.export(this.props.access_token, this.state.playlistOffset);
   },
 
   componentDidMount: function() {
@@ -123,7 +124,7 @@ var PlaylistTable = React.createClass({
                 <th style={{width: "100px"}}>Tracks</th>
                 <th style={{width: "120px"}}>Public?</th>
                 <th style={{width: "120px"}}>Collaborative?</th>
-                <th style={{width: "100px"}} className="text-right"><button className="btn btn-default btn-xs" type="submit" onClick={this.exportPlaylists}><span className="fa fa-file-archive-o"></span> Export All</button></th>
+                <th style={{width: "100px"}} className="text-right"><button className="btn btn-default btn-xs" type="submit" onClick={this.exportPlaylists}><span className="fa fa-file-archive-o"></span> Export Page</button></th>
               </tr>
             </thead>
             <tbody>
@@ -231,11 +232,11 @@ var Paginator = React.createClass({
 
 // Handles exporting all playlist data as a zip file
 var PlaylistsExporter = {
-  export: function(access_token, playlistCount) {
+  export: function(access_token, offset) {
     var playlistFileNames = [];
 
     window.Helpers.apiCall("https://api.spotify.com/v1/me", access_token).then(function(response) {
-      var limit = 20;
+      var limit = 50;
       var userId = response.id;
 
       // Initialize requests with starred playlist
@@ -246,13 +247,11 @@ var PlaylistsExporter = {
         )
       ];
 
-      // Add other playlists
-      for (var offset = 0; offset < playlistCount; offset = offset + limit) {
-        var url = "https://api.spotify.com/v1/users/" + userId + "/playlists";
-        requests.push(
-          window.Helpers.apiCall(url + '?offset=' + offset + '&limit=' + limit, access_token)
-        )
-      }
+      // Add playlists in current page
+      var url = "https://api.spotify.com/v1/users/" + userId + "/playlists";
+      requests.push(
+        window.Helpers.apiCall(url + '?offset=' + offset + '&limit=' + limit, access_token)
+      )
 
       $.when.apply($, requests).then(function() {
         var playlists = [];