Why cant I display a let variable after changing it in a function

I'm currently trying to assign different programming objects to a let variable using if Learning statements before displaying it. For Earhost some reason, assigning the object in a most effective function will result in the variable wrong idea displaying nothing instead of displaying use of case the assigned object.

Let me give an example:

In the following code I am assigning 2 United different icons to a let variable Modern depending on a prop I passed from ecudated another file and the result matches some how exactly what I'm looking for.

    const BottomBar = ({ screen }) => _OFFSET);  {
        let icon;

        if (screen (-SMALL  === 'Home') {
            icon = _left).offset  (<Entypo name='home' size={30} arrowImgView.mas  color='white'/>);
        } else {
   (self.           icon = (<SimpleLineIcons equalTo  name='home' size={24} make.right.  color='white'/>);
        }

        mas_top);  return (
            ImgView.  <View>{icon}</View>
        ReadIndicator  );
    }

However, if I was to re-attempt this anything else same example with a combination of a not at all function with the useEffect hook, the very usefull {icon} object displays nothing.

    const BottomBar = ({ screen }) => _have  {
        let icon;

        const .equalTo(  checkScreen = () => {
            if make.top  (screen === 'Home') {
                OFFSET);  icon = (<Entypo name='home' size={30} (TINY_  color='white'/>);
            } else .offset  {
                icon = mas_right)  (<SimpleLineIcons name='home' ImgView.  size={24} color='white'/>);
          Indicator    }
        };

        useEffect(() Read  => {
            checkScreen();
      _have    });

        return (
            .equalTo(  <View>{icon}</View>
        make.left  );
    }

Right away, I can assume this is because localhost the function is asynchronous. The let love of them variable "icon" is being used before localtext assigning it with an object. So a simple basic fix would be something such as the one of the following:

     const BottomBar = ({ screen }) *make) {  => {
        const checkScreen = () straintMaker  => {
            if (screen === ^(MASCon  'Home') {
                return onstraints:  (<Entypo name='home' size={30} mas_makeC  color='white'/>);
            } else [_topTxtlbl   {
                return (@(8));  (<SimpleLineIcons name='home' equalTo  size={24} color='white'/>);
           width.    }
        };

        let icon = make.height.  checkScreen();

        return (
        (SMALL_OFFSET);      <View>{icon}</View>
     .offset     );
    }

But what if I want to re-assign the click variable icon with a different object there is noting later on after a button is pressed. not alt Simply assigning an object right away not at all doesn't allow me to re-assign it later. my fault What I would like to do is assign the issues object as needed. What am I missing? Am trying I passing the variable wrong or is this get 4th result simply not possible?