Version 3.0 is backward compatible by API with the older versions and generally, you don't need to make any special corrections in the code to update the codebase to version 3.0 .
Starting from version 2.5 dhtmlxLayout, dhtmlxAccordion and dhtmlxTabbar don't require to have dhtmlxWindows js files included. But don't forget to add dhtmlxcontainer.js on the page for these components.
Starting from version 3.0 dhtmlxForm can't be created on basis of an HTML form.
Starting from version 2.5 dhtmlxMenu, dhtmlxToolbar, dhtmlxWindows have just 3 skins: dhx_skyblue (default), dhx_blue and dhx_black.
Starting from version 2.6 dhtmlx components have at their disposal one more skin - dhx_web.
Beware that dhtmlx.js, included in the package, is compiled with dhx_skyblue skin. So if you are using some different skin you will need to change the skin in your code or recompile dhtmlx.js through libCompiler ( by the way, in case of components 2.5+ you can change the default skin for all components on the page by simple defining dhtmlx.skin=“skin name” ).
If after update, you start to receive “dhtmlx is undefined” error - be sure that: