Use ES6 class syntax

lib/cartodb/models/dataview/list.js

@@ -12,26 +12,23 @@ var listSqlTpl = ctx => `select ${ctx._columns} from (${ctx._query}) as _cdb_lis
     }
 }
 */
+module.exports = class List extends BaseDataview{
+    constructor (query, options = {}) {
+        super();
 
-function List(query, options) {
+        this._checkOptions(options);
-    options = options || {};
-
-    if (!Array.isArray(options.columns)) {
-        throw new Error('List expects `columns` array in widget options');
-    }
-
-    BaseDataview.apply(this);
 
         this.query = query;
         this.columns = options.columns;
-}
+    }
 
-List.prototype = new BaseDataview();
+    _checkOptions (options) {
-List.prototype.constructor = List;
+        if (!Array.isArray(options.columns)) {
+            throw new Error('List expects `columns` array in widget options');
+        }
+    }
 
-module.exports = List;
+    sql (psql, override, callback) {
-
-List.prototype.sql = function(psql, override, callback) {
         if (!callback) {
             callback = override;
         }
@@ -42,22 +39,23 @@ List.prototype.sql = function(psql, override, callback) {
         });
 
         return callback(null, listSql);
-};
+    }
 
-List.prototype.format = function(result) {
+    format (result) {
         return {
             rows: result.rows
         };
-};
+    }
 
-List.prototype.getType = function() {
+    getType () {
         return TYPE;
-};
+    }
 
-List.prototype.toString = function() {
+    toString () {
         return JSON.stringify({
             _type: TYPE,
             _query: this.query,
             _columns: this.columns.join(', ')
         });
-};
+    };
+}