function draw() { var canvas = document.getElementById('canvas'); var ctx = canvas.getContext('2d'); // assign gradients to fill and stroke styles ctx.fillStyle = 'rgba(0,0,0,0)'; // or 'transparent' ctx.fillRect(50,25,50,100); // setting fillStyle to anything other than 'transparent' will fix this case. // ctx.fillStyle = 'red'; ctx.strokeStyle = 'green'; ctx.lineWidth = 5; ctx.beginPath(); ctx.moveTo(canvas.width/4, canvas.height/2); ctx.lineTo(canvas.width *3/8, canvas.height * 3/4); ctx.lineTo(canvas.width * 3/4, canvas.height /4); ctx.stroke(); }