replace prepend() calls since they aren't supported in IE11

src/components/modebar/modebar.js

@@ -88,7 +88,7 @@ proto.update = function(graphInfo, buttons) {
             }
 
             if(fullLayout.modebar.orientation === 'v') {
-                this.element.prepend(logoGroup);
+                Lib.prependElement(this.element, logoGroup);
             } else {
                 this.element.appendChild(logoGroup);
             }

src/lib/index.js

@@ -689,6 +689,19 @@ lib.removeElement = function(el) {
     if(elParent) elParent.removeChild(el);
 };
 
+lib.prependElement = function(el) {
+    var argArr = Array.prototype.slice.call(arguments);
+    argArr.splice(0, 1);
+    var docFrag = document.createDocumentFragment();
+
+    argArr.forEach(function(argItem) {
+        var isNode = argItem instanceof Node;
+        docFrag.appendChild(isNode ? argItem : document.createTextNode(String(argItem)));
+    });
+
+    el.insertBefore(docFrag, el.firstChild);
+};
+
 /**
  * for dynamically adding style rules
  * makes one stylesheet that contains all rules added

test/jasmine/assets/unpolyfill.js

@@ -18,5 +18,17 @@
                 ].join(' '));
             }
         });
+
+        Object.defineProperty(item, 'prepend', {
+            configurable: true,
+            enumerable: true,
+            writable: true,
+            value: function remove() {
+                throw Error([
+                    'test/jasmine/assets/unpolyfill.js error: calling ChildNode.prepend()',
+                    'which is not available in IE.'
+                ].join(' '));
+            }
+        });
     });
 })([Element.prototype, CharacterData.prototype, DocumentType.prototype]);