<canvas id="canvas"><canvas>

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

const canvasW = canvas.width;
const canvasH = canvas.height;

ctx.beginPath();
ctx.ellipse(300, 200, 300, 150, 0, 0, Math.PI * 2);
ctx.stroke();