Is it possible to make in Geany JavaScript autocompletion?
If it is possible it would be better if it will work without Ctrl+Space like in sublime
Unfortunately, your question is not very clear in terms what you expect from auto completion. Geany is supporting e.g. static tags -- which can be self generated or downloaded from the wiki. To enable them go to Tools->Load tags. Also it supports some session based autocompletion, which is turned on by default.
Please take care, as there is a difference between inline JavaScript and explicit JavaScript-file.