When updating element ,which default value false or null, error occurs TypeError: Cannot read property 'exvariable' of null

Question

I am working on nodejs express with mongoose. Every user has such as exvariable which controls permission to have exvariabletext.

My user model schema exvariable and exvariabletext;
exvariable : {type:Boolean,default:false},
exvariabletext:{type:String,default:null}

When I am trying to find user and check if(user.exvariable === false), I am getting an Error such like that
TypeError: Cannot read property 'exvariable' of null. So I can't use the default value and update it.

I have tried to change the default value in schema and control in nodejs syntax but couldn't pass the error and I want to understand the logic.

And my code like this;

router.post("/setexvariable",(req,res)=>{
    
    User.findById(req.params.id,(err,user)=>{
        if(err){
            console.log(err);
            req.flash("error","Oops, try again 😔");
            res.redirect("back");
        }
        
        if(user.exvariable == false){
            user.exvariable=true;
            user.exvariabletext=req.body.text;
            user.save();
            req.flash("success","Welcome 😍");
            res.redirect("/somewhere",{user:user});
        }else{
            req.flash("error","You already has a exvariable 😔");
            res.redirect("back");
        }
    });
});

Answer 1

You have to set the id parameter in your route to be able to access it with req.params.id. In your code, req.params.id is undefined, so your query returns null.

You should have something like router.post("/setexvariable/:id", (req, res) => {...}). More on route params in Express's documentation.