string errors -> Error

dialog-polyfill.js

@@ -177,13 +177,13 @@
      */
     showModal: function() {
       if (this.dialog_.hasAttribute('open')) {
-        throw 'Failed to execute \'showModal\' on dialog: The element is already open, and therefore cannot be opened modally.';
+        throw new Error('Failed to execute \'showModal\' on dialog: The element is already open, and therefore cannot be opened modally.');
       }
       if (!document.body.contains(this.dialog_)) {
-        throw 'Failed to execute \'showModal\' on dialog: The element is not in a Document.'
+        throw new Error('Failed to execute \'showModal\' on dialog: The element is not in a Document.');
       }
       if (!dialogPolyfill.dm.pushDialog(this)) {
-        throw 'Failed to execute \'showModal\' on dialog: There are too many open modal dialogs.'
+        throw new Error('Failed to execute \'showModal\' on dialog: There are too many open modal dialogs.');
       }
       this.show();
       this.openAsModal_ = true;
@@ -223,7 +223,7 @@
      */
     close: function(opt_returnValue) {
       if (!this.dialog_.hasAttribute('open')) {
-        throw 'Failed to execute \'close\' on dialog: The element does not have an \'open\' attribute, and therefore cannot be closed.'
+        throw new Error('Failed to execute \'close\' on dialog: The element does not have an \'open\' attribute, and therefore cannot be closed.');
       }
       this.setOpen(false);
 
@@ -303,7 +303,7 @@
           'may not work correctly', element);
     }
     if (element.nodeName.toUpperCase() != 'DIALOG') {
-      throw 'Failed to register dialog: The element is not a dialog.';
+      throw new Error('Failed to register dialog: The element is not a dialog.');
     }
     new dialogPolyfillInfo(/** @type {!HTMLDialogElement} */ (element));
   };