Динамическое рисование дуги canvas

var canvas = document.getElementById('cnvs'); 
var ctx = canvas.getContext('2d'); 
 
ctx.lineWidth = 15; 
ctx.strokeStyle = "#FF0000"; 
ctx.lineCap = "round"; 
 
ctx.arc(100, 100, 80, 2.355, 7.065, false); 
ctx.stroke();

<canvas id="cnvs" width="400px" height="400px"></canvas>