I have just downloaded unity and saw that now it supports Visual studio code, I downloaded it and made it the default editor.
After trying to edit a script, it prompted
Maybe too late, but for future comers ...
There is an extension now for visual studio code called MonoBehaviour Snippets by Rachod Petchpho.
Press Ctrl+shift+x
in the IDE to open extensions panel then search for MonoBehaviour Snippets
, install and reload the IDE, now you will find all the autocomplete for the function names and objects just like MonoDevelop.