How Refresh chart js data with same variable name

Question

I am facing an issue while refreshing the data using the same variable. Every time data get changed in a variable(mydata) but after an update the chart loaded with same data.while click the refresh button chart get reloded but always showing the old chart in chart

<button type="button" onclick="refresh()">Refresh</button> 
    <canvas id="mychart"></canvas>
    <script >
        var config = {
            type: 'bar',
            options: {
                scales: {
                    y: {
                        beginAtZero: true
                    }
                }
            },
        };
        var myChart=null;     
function refresh(){
    $.ajax({
                url: '/mydata',
                method: 'POST',
                data: {"user":user},
                async: false,
                success: function(data) {
                    mydata = data;
                }
            })
    config.data = {
            labels: ["jan","Feb","Mar","Apr","may","june","july"],
            datasets:
               [{
                  data: mydata,
                  backgroundColor: [
                    'rgba(255, 99, 132, 0.2)',
                    'rgba(255, 159, 64, 0.2)',
                    'rgba(255, 205, 86, 0.2)',
                    'rgba(75, 192, 192, 0.2)',
                    'rgba(54, 162, 235, 0.2)',
                    'rgba(153, 102, 255, 0.2)',
                    'rgba(201, 203, 207, 0.2)'
                ],
                borderColor: [
                    'rgb(255, 99, 132)',
                    'rgb(255, 159, 64)',
                    'rgb(255, 205, 86)',
                    'rgb(75, 192, 192)',
                    'rgb(54, 162, 235)',
                    'rgb(153, 102, 255)',
                    'rgb(201, 203, 207)'
                ]
               }]
         };
         ctx = document.getElementById('mychart');
    if(myChart == null){
        myChart = new Chart(ctx, config);
    } else{
    myChart.data.datasets[0].data=mydata;
       myChart.update();
    }

}
        
    </script>
</body>