Is it possible to change the mode of a FormView (say from ReadOnly to Edit) client-side using Javascript or is this only possible server-side?

Basically, changing the mode of a FormView reflects what controls (html) are rendered to the page.

Moving from read-only to edit for example would require rendering some text - boxes(inputs, instead of spans).

So I'm afraid this could not happen purely on client-side. You could use an update panel , so only an asyn post back is done and only

the form view html is refreshed.