function onInit() {
        trigger t = CreateTrigger();
       
        TriggerRegisterAnyUnitEventBJ(t, EVENT_PLAYER_UNIT_SPELL_EFFECT);
        TriggerAddCondition(t, Condition(function() -> boolean {
            integer abillvl;
            cfdata cf;
           
            // ----------------------------------------------------------------
            // *** condition ****
            if (GetSpellAbilityId() !=  CHAIN_FROST && GetSpellAbilityId() !=  CHAIN_FROST_UPGRADED)
                return false;
            // ----------------------------------------------------------------
               
            abillvl = GetUnitAbilityLevel(GetTriggerUnit(), GetSpellAbilityId());
            if (GetSpellAbilityId() ==  CHAIN_FROST_UPGRADED) abillvl += 1;
           
            // *** store data ***
            cf = cfdata.create(GetTriggerUnit(), GetSpellTargetUnit(), abillvl);
            cf.NewMissile(cf.caster);
            debug if (!IsUnitInRangeXY(cf.caster, cf.missile.X, cf.missile.Y, 100.) && !CHECK_MISSILE_POSITION)
                BJDebugMsg("|cffff0000Error:|rChain Frost missile not created at caster position, please enable \"CHECK_MISSILE_POSITION\".");
            //UnitShareVision(cf.target, cf.owner, true);
//* * *