Plotting a semi circle

create a plot describing a semi-circle.

HTML

<!-- Graph layout with semi circle plotted -->  
<body>
    <canvas id="myCanvas" width="578" height="500"></canvas>
  </body>

CSS

body {
        margin: 0px;
        padding: 0px;
      }

JavaScript

var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');

var width = 500;
var height = 500;

var radius = size/2;
    context.save();
    context.beginPath();
    context.translate(x, y);
    context.arc(0,0,radius,0,2 * Math.PI, true);
    context.fillStyle=style;
    context.fill();
    context.restore();// whole circle in grey