Why the colorpicker demo send ajax request every time when you change the c

Why the colorpicker demo send ajax request every time when you change the color?
I mean is it difficult to write client only functionality in vaadin?
The colorPicker demo is here
http://demo.vaadin.com/sampler/#foundation/cssinject

Most likely because it sends its current value to the server side so that a ValueChangeEvent can be fired. Vaadin is predominately a server-side framework, so all core widgets do this (see the setImmediate method JavaDoc for information about controlling this behavior).

About the difficulty of creating client-side-only functionality, it really depends what you want to do. As of Vaadin 7 we include GWT in Vaadin, so you can use that to build whatever you want :slight_smile: