Assuming RWEP is RunWithElevatedPrivileges...

CSOM (Managed or JS) accesses SharePoint via the REST web services and only has the permissions of the caller. There is no RunWithElevatedPrivileges for code not running from the server side API. Although, the app can have greater permissions than the user. (See the links below.)

CSOM (Managed or JS) gets permissions:

• From the logged in user (SharePoint Hosted app or something running on the SP server.)
• App permissions (when running as an app)

To better answer your question:

• How / where is your CSOM running?
• Is the list in the app site, or elsewhere in SharePoint?
• Does the user running the code already have Add/Edit/Update permissions?

By the way, when searching MSDN, SharePoint apps are now "SharePoint Add-ins".

https://technet.microsoft.com/en-us/library/jj219576.aspx

http://blogs.msdn.com/b/officeapps/archive/2013/09/25/use-sharepoint-permission-management-to-create-various-roles-in-an-app-for-sharepoint.aspx

https://msdn.microsoft.com/en-us/library/office/fp142383.aspx

Assuming RWEP is RunWithElevatedPrivileges...

CSOM (Managed or JS) accesses SharePoint via the REST web services and only has the permissions of the caller. There is no RunWithElevatedPrivileges for code not running from the server side API. Although, the app can have greater permissions than the user. (See the links below.)

CSOM (Managed or JS) gets permissions:

• From the logged in user (SharePoint Hosted app or something running on the SP server.)
• App permissions (when running as an app)

To better answer your question:

• How / where is your CSOM running?
• Is the list in the app site, or elsewhere in SharePoint?
• Does the user running the code already have Add/Edit/Update permissions?

By the way, when searching MSDN, SharePoint apps are now "SharePoint Add-ins".

https://technet.microsoft.com/en-us/library/jj219576.aspx

http://blogs.msdn.com/b/officeapps/archive/2013/09/25/use-sharepoint-permission-management-to-create-various-roles-in-an-app-for-sharepoint.aspx

https://msdn.microsoft.com/en-us/library/office/fp142383.aspx