Check that container is a valid DOM element

src/core/ReactComponent.js

@@ -511,6 +511,10 @@ var ReactComponent = {
         container,
         transaction,
         shouldReuseMarkup) {
+      invariant(
+        container && container.nodeType === 1,
+        'mountComponentIntoNode(...): Target container is not a DOM element.'
+      );
       var renderStart = Date.now();
       var markup = this.mountComponent(rootID, transaction);
       ReactMount.totalInstantiationTime += (Date.now() - renderStart);

src/core/ReactMount.js

@@ -35,7 +35,7 @@ var containersByReactRootID = {};
  * @return {?*} DOM element that may have the reactRoot ID, or null.
  */
 function getReactRootElementInContainer(container) {
-  return container.firstChild;
+  return container && container.firstChild;
 }
 
 /**

src/core/__tests__/ReactComponent-test.js

@@ -31,6 +31,24 @@ describe('ReactComponent', function() {
     reactComponentExpect = require('reactComponentExpect');
   });
 
+  it('should throw on invalid render targets', function() {
+    var container = document.createElement('div');
+    // jQuery objects are basically arrays; people often pass them in by mistake
+    expect(function() {
+      React.renderComponent(<div></div>, [container]);
+    }).toThrow(
+      'Invariant Violation: mountComponentIntoNode(...): Target container is ' +
+      'not a DOM element.'
+    );
+
+    expect(function() {
+      React.renderComponent(<div></div>, null);
+    }).toThrow(
+      'Invariant Violation: mountComponentIntoNode(...): Target container is ' +
+      'not a DOM element.'
+    );
+  });
+
   it('should throw when supplying a ref outside of render method', function() {
     var instance = <div ref="badDiv" />;
     expect(function() {