Click on scrollbar throws error element.is is not a function

[victor-kirillov]

Are you reporting a feature or a bug?

Bug

Provide detailed reproduction steps (if any)

1. Add widget plugin or some plugin used it, for example upload image plugin in ckeditor build
2. Make editor scrollable
3. Click on scrollbar

Expected result

No error in the console.

Actual result

An error in the console:

Uncaught TypeError: element.is is not a function

Other details

An error comes from widget plugin: https://github.com/ckeditor/ckeditor-dev/blob/master/plugins/widget/plugin.js#L448

Can be simply reproduced on that page: http://sdk.ckeditor.com/samples/simplebox.html

Possible solution: add check if element has an is function here - https://github.com/ckeditor/ckeditor-dev/blob/master/plugins/widget/plugin.js#L452

There is similar issue #528 #515

• Browser: Chrome 59
• OS: Windows 10
• CKEditor version: 4.7.1
• Installed CKEditor plugins: Full version with upload image plugin and all required plugins