Add Image to Canvas

canvas_image.js

window.onload = function ()
{
  var canvas = document.getElementById("overlay_canvas");
  var ctx = canvas.getContext("2d");
  var image = new Image();
  image.src = "http://placekitten.com/4536/3024";
  image.onload = function () {
    ctx.drawImage(image, 0, 0);
    image_ctx = image.getContext("2d");
    debugger;
  }

}