pveproxy with ExtJS 5 developpement mini howto
unpack the ExtJS 5 sources, and copy them to /usr/share/pve-manager/ext5
cd www/ext5/
make install
symlink the to our ext5 compatible javascript code
cd /usr/share/pve-manager
ln -s PATH_TO_YOUR_GIT_REPO/www/manager5
access the PVE proxy with ExtJS 5
https://localhost:8006/?ext5=1
With the extra parameter ext5=1, pve-proxy will call the function PVE::ExtJSIndex5::get_index() which returns a HTML page, with all javascript files included. Provided you included the javascript in PVE/ExtJSIndex5.pm, a simple browser refresh is then enough to see your changes.