Ensure null values sort last

src/lib.js

@@ -152,7 +152,22 @@ export function sorted_items(items, sort, sortings) {
   }
 
   if (sort.field) {
-    return orderBy(items, sort.field, sort.order || 'asc');
+    const fields = Array.isArray(sort.field) ? sort.field : [sort.field];
+    const orders = Array.isArray(sort.order) ? sort.order : [sort.order || 'asc'];
+
+    // push null/undefined to the end for each field by prefixing with a boolean iteratee
+    const iteratees = [];
+    const iterateeOrders = [];
+
+    fields.forEach((field, idx) => {
+      iteratees.push((item) => (item[field] === null || item[field] === undefined ? 1 : 0));
+      iterateeOrders.push('asc'); // keep non-null before nulls
+
+      iteratees.push(field);
+      iterateeOrders.push(orders[idx] || 'asc');
+    });
+
+    return orderBy(items, iteratees, iterateeOrders);
   }
 
   return items;

tests/sortingSpec.js

@@ -22,6 +22,13 @@ describe('aggregations', function () {
     },
   ];
 
+  const itemsWithNulls = [
+    { name: 'movie1', rating: null },
+    { name: 'movie2', rating: 5 },
+    { name: 'movie3', rating: null },
+    { name: 'movie4', rating: 3 },
+  ];
+
   it('makes items sorting', function test(done) {
     const sortings = {
       name_asc: {
@@ -72,6 +79,24 @@ describe('aggregations', function () {
       'movie7',
       'movie2',
     ]);
+
+    // nulls should be last regardless of order
+    const nullSortings = {
+      rating_desc: {
+        field: 'rating',
+        order: 'desc',
+      },
+      rating_asc: {
+        field: 'rating',
+        order: 'asc',
+      },
+    };
+
+    result = sorted_items(itemsWithNulls, 'rating_desc', nullSortings);
+    assert.deepEqual(map(result, 'rating'), [5, 3, null, null]);
+
+    result = sorted_items(itemsWithNulls, 'rating_asc', nullSortings);
+    assert.deepEqual(map(result, 'rating'), [3, 5, null, null]);
     done();
   });
 });