Global adding option to Combo

I have on page big count of Combo

var z1 = new dhtmlXCombo("combo_zone1", "alfa3", 200);
var z2 = new dhtmlXCombo("combo_zone2", "alfa3", 200);
var z3 = new dhtmlXCombo("combo_zone3", "alfa3", 200);

I need add option

addOption([ ["a","option A"] ]); to all Combo.
I don’t want to use search z1…z3 on page.
How can I do it?

Done with Angular (with difficulty)!
But maybe do other good ways exist?