fix #101: Slice filter does not work on arrays

src/filters.js

@@ -40,7 +40,7 @@ const filters = {
   'escape_once': str => escape(unescape(str)),
   'first': v => v[0],
   'floor': v => Math.floor(v),
-  'join': (v, arg) => v.join(arg),
+  'join': (v, arg) => v.join(arg === undefined ? ' ' : arg),
   'last': v => _.last(v),
   'lstrip': v => stringify(v).replace(/^\s+/, ''),
   'map': (arr, arg) => arr.map(v => v[arg]),
@@ -61,8 +61,10 @@ const filters = {
   },
   'rstrip': str => stringify(str).replace(/\s+$/, ''),
   'size': v => v.length,
-  'slice': (v, begin, length) =>
-    v.substr(begin, length === undefined ? 1 : length),
+  'slice': (v, begin, length) => {
+    if (length === undefined) length = 1
+    return v.slice(begin, begin + length)
+  },
   'sort': (v, arg) => v.sort(arg),
   'split': (v, arg) => stringify(v).split(arg),
   'strip': (v) => stringify(v).trim(),

test/unit/filters.js

@@ -154,10 +154,17 @@ describe('filters', function () {
     it('should return "3" for 3.5', () => test('{{ "3.5" | floor }}', '3'))
   })
 
-  it('should support join', function () {
-    const src = '{% assign beatles = "John, Paul, George, Ringo" | split: ", " %}' +
-      '{{ beatles | join: " and " }}'
-    return test(src, 'John and Paul and George and Ringo')
+  describe('join', function () {
+    it('should support join', function () {
+      const src = '{% assign beatles = "John, Paul, George, Ringo" | split: ", " %}' +
+        '{{ beatles | join: " and " }}'
+      return test(src, 'John and Paul and George and Ringo')
+    })
+    it('should default separator to space', function () {
+      const src = '{% assign beatles = "John, Paul, George, Ringo" | split: ", " %}' +
+        '{{ beatles | join }}'
+      return test(src, 'John Paul George Ringo')
+    })
   })
 
   it('should support split/last', function () {
@@ -277,6 +284,7 @@ describe('filters', function () {
     it('should slice third char by 2', () => test('{{ "Liquid" | slice: 2 }}', 'q'))
     it('should slice substr by 2,5', () => test('{{ "Liquid" | slice: 2, 5 }}', 'quid'))
     it('should slice substr by -3,2', () => test('{{ "Liquid" | slice: -3, 2 }}', 'ui'))
+    it('should support array', () => test('{{ "1,2,3,4" | split: "," | slice: 1,2 | join }}', '2 3'))
   })
 
   it('should support sort', function () {