index.js

/* 

//You should already have initialised your stack navigator and named it AppNavigator (you can call it something else just change all the references)
//eg.

const AppNavigator = StackNavigator(
    Routes
);

*/

//we're saving the default getStateForAction 
const prevGetStateForAction = AppNavigator.router.getStateForAction;

AppNavigator.router = {
    ...AppNavigator.router,
    getStateForAction(action, state) {

        
    
    //check if route is already on stack and go to it instead of adding a new item on stack
    //NOTE: This will break things like being able to have push notification messages on the same route but different messages and being able to go back through them
    //if that becomes a problem just opt out for certain route names eg  if(action.routeName == "Messages") return prevGetStateForAction(aciton,state)
    
    if(state && action.type == 'Navigation/NAVIGATE' && state.routes !== undefined ) {
        //console.log("getStateForAction state",state,"action,",action);
        var i = -1;


        //try find the route in the stack
        for(var c =0; c < state.routes.length; c++) {
            if(state.routes[c].routeName == action.routeName) {
                i = c;
                break;
            }
        }

        //found it but we're already there so do nothing as we're trying to navigate to ourselves
        if(i == state.index) {
            console.log("getstateforaction() - you're trying to navigate to yourself!");
            return null;
        }

        //didn't find it - add screen to stack - ie call default action
        if(i == -1) {
            console.log("getstateforaction() - no duplicate screen found");
            return prevGetStateForAction(action,state);        
        }

        //found it - move it to just after index and increment index - i think
        console.log("stacknavigator is trying to duplicate route - moving back to previous route");

        var route = state.routes[i];
        var routes = state.routes;
        routes.splice(i,1);
        routes = [
            ...routes,
            route
        ];

        newIndex = routes.length-1;

        return {
            ...state,
            routes: routes,
            index: newIndex
        }
    }

    return prevGetStateForAction(action,state);
}
}