containsTracks method
Implementation
Future<Map<String, bool>> containsTracks(List<String> ids) async {
assert(ids.isNotEmpty, 'No track ids were provided');
final limit = ids.length < 50 ? ids.length : 50;
final idsParam = ids.sublist(0, limit).join(',');
final jsonString = await _api._get('$_path/contains?ids=$idsParam');
final list = List.castFrom<dynamic, bool>(json.decode(jsonString));
return Map.fromIterables(ids, list);
}