Fix bindto to accept null and empty string

c3.js

@@ -158,7 +158,15 @@
         if ($$.initBrush) { $$.initBrush(); }
         if ($$.initZoom) { $$.initZoom(); }
 
-        $$.selectChart = typeof config.bindto.node === 'function' ? config.bindto : d3.select(config.bindto);
+        if (!config.bindto) {
+            $$.selectChart = d3.selectAll([]);
+        }
+        else if (typeof config.bindto.node === 'function') {
+            $$.selectChart = config.bindto;
+        }
+        else {
+            $$.selectChart = d3.select(config.bindto);
+        }
         if ($$.selectChart.empty()) {
             $$.selectChart = d3.select(document.createElement('div')).style('opacity', 0);
             $$.observeInserted($$.selectChart);
@@ -864,7 +872,12 @@
     };
 
     c3_chart_internal_fn.observeInserted = function (selection) {
-        var $$ = this, observer = new MutationObserver(function (mutations) {
+        var $$ = this, observer;
+        if (typeof MutationObserver === 'undefined') {
+            window.console.error("MutationObserver not defined.");
+            return;
+        }
+        observer= new MutationObserver(function (mutations) {
             mutations.forEach(function (mutation) {
                 if (mutation.type === 'childList' && mutation.previousSibling) {
                     observer.disconnect();

spec/core-spec.js

@@ -54,14 +54,52 @@ describe('c3 chart', function () {
 
     describe('bindto', function () {
 
-        it('should accept d3.selection object', function () {
-            args.bindto = d3.select('#chart');
-            expect(true).toBeTruthy();
+        describe('selector', function () {
+            it('update args', function () {
+                d3.select('#chart').html('');
+                args.bindto = '#chart';
+                expect(true).toBeTruthy();
+            });
+            it('should be created', function () {
+                var svg = d3.select('#chart svg');
+                expect(svg.size()).toBe(1);
+            });
         });
 
-        it('should be created', function () {
-            var svg = d3.select('#chart svg');
-            expect(svg).not.toBeNull();
+        describe('d3.selection object', function () {
+            it('update args', function () {
+                d3.select('#chart').html('');
+                args.bindto = d3.select('#chart');
+                expect(true).toBeTruthy();
+            });
+            it('should be created', function () {
+                var svg = d3.select('#chart svg');
+                expect(svg.size()).toBe(1);
+            });
+        });
+
+        describe('null', function () {
+            it('update args', function () {
+                d3.select('#chart').html('');
+                args.bindto = null;
+                expect(true).toBeTruthy();
+            });
+            it('should not be created', function () {
+                var svg = d3.select('#chart svg');
+                expect(svg.size()).toBe(0);
+            });
+        });
+
+        describe('empty string', function () {
+            it('update args', function () {
+                d3.select('#chart').html('');
+                args.bindto = '';
+                expect(true).toBeTruthy();
+            });
+            it('should not be created', function () {
+                var svg = d3.select('#chart svg');
+                expect(svg.size()).toBe(0);
+            });
         });
 
     });

src/core.js

@@ -153,7 +153,15 @@ c3_chart_internal_fn.initWithData = function (data) {
     if ($$.initBrush) { $$.initBrush(); }
     if ($$.initZoom) { $$.initZoom(); }
 
-    $$.selectChart = typeof config.bindto.node === 'function' ? config.bindto : d3.select(config.bindto);
+    if (!config.bindto) {
+        $$.selectChart = d3.selectAll([]);
+    }
+    else if (typeof config.bindto.node === 'function') {
+        $$.selectChart = config.bindto;
+    }
+    else {
+        $$.selectChart = d3.select(config.bindto);
+    }
     if ($$.selectChart.empty()) {
         $$.selectChart = d3.select(document.createElement('div')).style('opacity', 0);
         $$.observeInserted($$.selectChart);
@@ -859,7 +867,12 @@ c3_chart_internal_fn.updateDimension = function (withoutAxis) {
 };
 
 c3_chart_internal_fn.observeInserted = function (selection) {
-    var $$ = this, observer = new MutationObserver(function (mutations) {
+    var $$ = this, observer;
+    if (typeof MutationObserver === 'undefined') {
+        window.console.error("MutationObserver not defined.");
+        return;
+    }
+    observer= new MutationObserver(function (mutations) {
         mutations.forEach(function (mutation) {
             if (mutation.type === 'childList' && mutation.previousSibling) {
                 observer.disconnect();