View difference between Paste ID: bV4aMvEu and 5jY5Tviq

 let userFields = {
     id: {
         dbFields: 'id',
     },
     email: {
         dbFields: 'email',
     },
     first_name: {
         dbFields: 'first_name',
     },
     last_name: {
         dbFields: 'last_name',
     },
     name: {
         dbFields: ['first_name', 'last_name'],
         resolve: user =>
             [user.first_name, user.last_name]
             .filter(n => n.length)
             .join(' '),
     }
 };
 
 let selectFields = ['name', 'first_name', 'email'];
 
 function ensureArray(x) {
     return x instanceof Array ? x : [x];
 }
 
 function concat(arrays) {
     return [].concat.apply([], arrays);
 }
 
 function uniquify(array) {
-    let s = new Set();
+    let s = new Set(array);
-    for (let x of array)
+
-        s.add(x);
+
 
 var dbFieldsPerSelect =
     selectFields
     .map(name => userFields[name].dbFields)
     .map(ensureArray);
 
 var dbFields = uniquify(concat(dbFieldsPerSelect));
 
 console.log(dbFields);