Basic node.js middlewares

This code return "var2 is not defined", how can I use the var2 in router.get('/').. sentence?

Thanks in advance

    `//router

    var express = require('express');
    var router = express.Router();

    router.use('/', function(req, res, next){
        var2: "That is a var 2";
        next();
    });

    router.get('/', function(req, res, next){
        res.send(var2);
    });

    module.exports = router;`