SyntaxError: Unexpected end of JSON input in my simple node application..not able to fetch data

here is the server side!!i am using express server and upon deploying it on heroku it doesnt work as expected.!!

    const express = require("express")
    const app = express();
    let PORT = process.env.PORT || 3000;
    
    app.use(express.static("./public"));
    app.use(express.json())
    const fs = require('fs');
    let data = JSON.parse(fs.readFileSync('./public/data.json','utf-8'));
    app.get("/extra/:year", (req, res) => {
        
       let year = req.params.year;
        res.json(data.extraRunsPerTeam2016[year])
      })
    
    app.get("/economy", (req, res) => {
       if (!req.query.season1) {
            return res.send(
                {
                    error: "this is not the season"
                })
        }
    
    console.log(data.economicalBowler2015)
        res.send(
            res.json(data.economicalBowler2015)
        )
    })
    
    
    app.listen(PORT, () => {
        console.log("server is up and running !! please check http://localhost:3000/")
    })

one of the client side!

    function show() {
         let year = document.getElementById("season").value;
    
        if (year == "") {
            alert("please select SEASON from the drop down list ")
        }
    
        // fetch('/extra?season=' + year)
        fetch(`/extra/${year}`)
            .then((resp) => resp.json())
            .then(resp => {            
        // visualizeData(resp);
            setTimeout(function(){ return visualizeData(resp); }, 3000);
    
    function visualizeData(data) {
                    let a = [];
                    for (let i in data) {
                        a.push([i, data[i]])
                    }
    
         Highcharts.chart("extra-Runs", {
                        chart: {
                            type: 'column'
                        },
                        title: {
    "its completed "
    }})

here im using highcharts to project the data into graph form.. in localhost its working but on the deployment its not working please someone help!!