HTML:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> </head> <body> <canvas id="ctx" width="300" height="300" style="border:1px solid #d3d3d3;"> </canvas </body> </html>
JS:
var c = document.getElementById('ctx')
var ctx = c.getContext('2d');
var x = 100;
var y = 50;
var RADIUS = 80;
ctx.beginPath();
ctx.arc(x, y, RADIUS, Math.PI / 2, Math.PI); //sAngle 90 ,eAngle 180
ctx.fillStyle = '#333';
ctx.lineTo(x, y);
ctx.fill();
ctx.restore();
ctx.stroke();