clearRectの使い方が分からない

なぜこれでキャンバス上のグラフが消えないのかが知りたいです。clearRectが上手く動いていないです。

html
1<!DOCTYPE html>
2<html lang="en">
3
4<head>
5  <meta charset="UTF-8">
6  <meta http-equiv="X-UA-Compatible" content="IE=edge">
7  <meta name="viewport" content="width=device-width, initial-scale=1.0">
8  <title>Document</title>
9  <script src="https://cdn.jsdelivr.net/npm/chart.js@2.9.4/dist/Chart.min.js"
10    integrity="sha384-zNy6FEbO50N+Cg5wap8IKA4M/ZnLJgzc6w2NqACZaK0u0FXfOWRRJOnQtpZun8ha"
11    crossorigin="anonymous"></script>
12</head>
13
14<body>
15  <canvas id="canvas"></canvas>
16
17  <script>
18    var ctx = document.getElementById('canvas')
19    var myChart = new Chart(ctx, {
20      type: 'line',
21      data: {
22        labels: [
23          'Sunday',
24          'Monday',
25          'Tuesday',
26          'Wednesday',
27          'Thursday',
28          'Friday',
29          'Saturday'
30        ],
31        datasets: [{
32          data: [
33            15339,
34            21345,
35            18483,
36            24003,
37            23489,
38            24092,
39            12034
40          ],
41          lineTension: 0,
42          backgroundColor: 'transparent',
43          borderColor: '#007bff',
44          borderWidth: 4,
45          pointBackgroundColor: '#007bff'
46        }]
47      },
48      options: {
49        scales: {
50          yAxes: [{
51            ticks: {
52              beginAtZero: false
53            }
54          }]
55        },
56        legend: {
57          display: false
58        }
59      }
60    })
61    ctx.clearRect(0, 0, ctx.clientWidth, ctx.clientHeight);
62  </script>
63</body>
64
65</html>