TowerMapHelper.js

({
    initHelper : function(component, event, helper) {
        helper.utilSetMarkers(component, event, helper);
    },
    
    utilSetMarkers: function(component, event, helper){
        //Variables declared with the let keyword can have Block Scope.
        //{ let x = 2; } x cannot be uset outside the block
        var action = component.get("c.getAllTowers");
        action.setCallback(this, function(response){
            var state = response.getState();
            if(state == 'SUCCESS') {
                const data = response.getReturnValue();
                const dataSize = data.length;
                const markers = [];
                for(let index = 0; index < dataSize-1; index++) {
                    const Tower = data[index];
                    markers.push({
                        'location': {
                             'Latitude' : Tower.Location__Latitude__s,
                             'Longitude' : Tower.Location__Longitude__s
                        },
                        'icon': 'utility:Tower',
                        'title' : Tower.Name,
                        'description' : Tower.Name + ' Tower Location at ' + Tower.State__r.Name
                   });
                }
                component.set("v.markersTitle", "Out and About Communications Tower Locations");
                component.set("v.mapMarkers", markers);
            }
        });
        $A.enqueueAction(action);
    }
    
})