All values in Liquid are truthy except nil and false.

src/syntax.js

@@ -43,12 +43,11 @@ function evalValue(str, scope) {
 }
 
 function isTruthy(val) {
-    if (val instanceof Array) return !!val.length;
-    return !!val;
+    return !isFalsy(val);
 }
 
 function isFalsy(val) {
-    return !isTruthy(val);
+    return false === val || undefined === val || null === val;;
 }
 
 module.exports = {

tags/for.js

@@ -36,7 +36,9 @@ module.exports = function(liquid) {
 
         render: function(scope, hash) {
             var collection = Liquid.evalExp(this.collection, scope);
-            if (Liquid.isFalsy(collection)) {
+
+            if (!Array.isArray(collection) || 
+                (Array.isArray(collection) && collection.length === 0)) {
                 return liquid.renderer.renderTemplates(this.elseTemplates, scope);
             }
 

test/tags/for.js

@@ -10,6 +10,7 @@ describe('tags/for', function() {
         ctx = {
             one: 1,
             alpha: ['a', 'b', 'c'],
+            emptyArray: []
         };
     });
     it('should support for', function() {
@@ -24,6 +25,12 @@ describe('tags/for', function() {
             .to.be.rejectedWith(/tag .* not closed/);
     });
 
+    it('should return else when for in empty array', function() {
+        var src = '{%for c in emptyArray%}a{%else%}b{%endfor%}';
+        return expect(liquid.parseAndRender(src, ctx))
+            .to.eventually.equal('b');
+    });
+
     it('should support for else', function() {
         var src = '{%for c in ""%}a{%else%}b{%endfor%}';
         return expect(liquid.parseAndRender(src, ctx))
@@ -80,13 +87,13 @@ describe('tags/for', function() {
             .to.eventually.equal('21');
     });
 
-    it('should support for reversed in the middle position', function() {
+    it('should support for reversed in the first position', function() {
         var src = '{% for i in (1..5) reversed limit:2 %}{{ i }}{% endfor %}';
         return expect(liquid.parseAndRender(src, ctx))
             .to.eventually.equal('21');
     });
 
-    it('should support for reversed in the first position', function() {
+    it('should support for reversed in the middle position', function() {
         var src = '{% for i in (1..5) offset:2 reversed limit:4 %}{{ i }}{% endfor %}';
         return expect(liquid.parseAndRender(src, ctx))
             .to.eventually.equal('543');

test/tags/if.js

@@ -8,6 +8,7 @@ describe('tags/if', function() {
     var ctx = {
         one: 1,
         two: 2,
+        emptyString: '',
         emptyArray: []
     };
 
@@ -19,7 +20,7 @@ describe('tags/if', function() {
     it('should support if 2', function() {
         var src = '{%if emptyArray%}a{%endif%}';
         return expect(liquid.parseAndRender(src, ctx))
-            .to.eventually.equal('');
+            .to.eventually.equal('a');
     });
     it('should support if 3', function() {
         var src = '{% if 2==3 %}yes{%else%}no{%endif%}';
@@ -46,4 +47,9 @@ describe('tags/if', function() {
         return expect(liquid.parseAndRender(src, ctx))
             .to.eventually.equal('');
     });
+    it('should return true if empty string', function() {
+        var src = "{%if emptyString%}a{%endif%}";
+        return expect(liquid.parseAndRender(src, ctx))
+            .to.eventually.equal('a');
+    });
 });

test/tags/unless.js

@@ -7,12 +7,13 @@ describe('tags/unless', function() {
     var liquid = Liquid();
 
     it('should render else when predicate yields true', function() {
-        var src = '{% unless 1 %}yes{%else%}no{%endunless%}';
+        // 0 is truthy
+        var src = '{% unless 0 %}yes{%else%}no{%endunless%}';
         return expect(liquid.parseAndRender(src))
             .to.eventually.equal('no');
     });
     it('should render unless when predicate yields false', function() {
-        var src = '{% unless 0 %}yes{%else%}no{%endunless%}';
+        var src = '{% unless false %}yes{%else%}no{%endunless%}';
         return expect(liquid.parseAndRender(src))
             .to.eventually.equal('yes');
     });