Use Checkboxes to make New Array

I have 3 checkboxes corresponding to 3 arrays.

On button press, I want to check which boxes are selected and then make a new array containing the selected 1-3 arrays.

I cannot make the new array from the checkbox choices - have commented where stuck:

JS Fiddle here

also - apologies - it's in this js fiddle but i cannot seem to get the JS to appear correctly in this stack overflow post. Function in question is addCategories.

`function addCategories() {}'