function createCircle(size, color) {
    const canvas = document.createElement("CANVAS");
    canvas.width = size;
    canvas.height = size;
    const context = canvas.getContext('2d');
    context.clearRect(0, 0, canvas.width, canvas.height);
    context.fillStyle = color;
    context.beginPath();
    context.arc(200, 200, 80, 0, 2 * Math.PI);
    context.fill();
    return canvas.toDataURL('image/png');
}

const base64 = createCircle(100, 'red');
console.log(base64);

document.getElementById('test').src = base64;

<img width="100" height="100" id="test" style="border: 1px solid black">