Chartjs-Chart js loading screen

<canvas id="canvas"></canvas>
<progress id="animationProgress" max="1" value="0" style="width: 100%"></progress> // you missed this html
        
var MONTHS = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];
        var progress = document.getElementById('animationProgress'); // and missed this
        
      
        var config = {
            type: 'line',
            data: {
                labels: ["January", "February", "March", "April", "May", "June", "July"],
                datasets: []// your dataset
            },
            options: {
                title:{
                    display:true,
                    text: "Progress Bar"
                },
                animation: {
                    duration: 2000,
                    onProgress: function(animation) {
                        //add progress
                        progress.value = animation.currentStep / animation.numSteps;
                    },
                    onComplete: function(animation) {
                        window.setTimeout(function() {
                            progress.value = 0;
                        }, 2000);
                    }
                }
            }
        };

        window.onload = function() {
            var ctx = document.getElementById("canvas").getContext("2d");
            window.myLine = new Chart(ctx, config);
        };