Uncaught TypeError: Failed to execute 'drawImage' on 'CanvasRenderingContext2D': The provided value is not of type '(HTMLImageElement or HTMLVideoElement or HTMLCanvasElement or ImageBitmap)'

drawImage — index.html:39TypeError: Type error

window.addEventListener('load', eventWindowLoadew,false);
function eventWindowLoadew(){
  canvasApp();
}
function canvasSupport(){
  return Modernizr.canvas;
}
function canvasApp(){
  if(!canvasSupport()){
    return;
  } else {
    var canvas = document.getElementById("mycanvas");
    var ctx = canvas.getContext("2d");
  }
  drawScreen();

  var image1 = new Image();
  image1.src = "mon_024.png";
  image1.addEventListener("load", eventMonsterLoaded, false);

  function eventMonsterLoaded(){
    drawScreen();
  }
  function drawScreen(){
      ctx.drawImage(image1, 0, 0); //39行目です。ここにエラーがでます。
  }
}