<canvas id="canvas" height="200">

canvas {
  border: 1px solid #000;
}

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

ctx.strokeStyle = 'purple';
ctx.strokeStyle = '#800080';
ctx.strokeStyle = 'rgb(128, 0, 128)';
ctx.strokeStyle = 'rgba(128, 0, 128, 1)';
ctx.strokeRect(50,50,100,100);