setting undefined as stringed "undefined"

Smaller undefined check

More descriptive comment

Added test for undefined variable to use undefined as string

Moved test and made it async

Fixed undefined value test

Author: vincentorback

lib/resolve-decl.js

@@ -143,10 +143,18 @@ function resolveDecl(decl, map, /*optional*/shouldPreserve, /*optional*/logResol
 	if(shouldPreserve === true && decl.value !== valueResults.value) {
 		decl.cloneAfter();
 	}
-
-	// Set the new value after we are done dealing with at-rule stuff
-	decl.value = valueResults.value;
-}
+
+
+	// Set 'undefined' value as a string to avoid making other plugins down the line unhappy
+	// See #22
+	if (valueResults.value === undefined) {
+		valueResults.value = 'undefined';
+	}
+
+
+	// Set the new value after we are done dealing with at-rule stuff
+	decl.value = valueResults.value;
+}
 
 
 

test/test.js

@@ -186,6 +186,25 @@ describe('postcss-css-variables', function() {
 	describe('missing variable declarations', function() {
 		test('should work with missing variables', 'missing-variable-usage');
 		test('should use fallback value if provided with missing variables', 'missing-variable-should-fallback');
+		it('should use string values for `undefined` values, see #22', function() {
+			return fs.readFileAsync('./test/fixtures/missing-variable-usage.css', 'utf8')
+				.then(function(buffer) {
+					var contents = String(buffer);
+						return postcss([
+							cssvariables()
+						])
+						.process(contents)
+						.then(function(result) {
+							var root = result.root;
+							var fooRule = root.nodes[0];
+							expect(fooRule.selector).to.equal('.box-foo');
+							var colorDecl = fooRule.nodes[0];
+							expect(colorDecl.value).to.be.a('string');
+							expect(colorDecl.value).to.be.equal('undefined');
+							return colorDecl.value;
+						});
+					});
+		});
 	});
 
 	it('should not parse malformed var() declarations', function() {
@@ -207,5 +226,4 @@ describe('postcss-css-variables', function() {
 		);
 	});
 
-
 });