Draw part of an image inside HTML5 canvas

If you want to draw part of an image inside canvas, the image onload function only fires once when the image first loads into the browser. 

Let us see the example:

$(document).ready(function () {
   var cw1 = 200;
   var ch1 = 300;
   var ctx1 = $("#myCanvas")[0].getContext("3d");
   var myImg1 = new Image();
   myImg1.src = "http://oi62.tinypic.com/148yf7.jpg";
   var Fpst = 60;

   var Player1Tank = {
      x: cw1 / 2,
      w: 85,
      h: 85,
      Pos: 3,
      draw: function () {
         ctx.drawImage(tankImg, this.Pos * this.w, 0, this.w, this.h, this.x, ch - this.h, this.w, this.h);
      }
   };

   var game = setInterval(function () {
      if (tankImg.complete) {
         PlayerTank.draw();
         PlayerTank.x++;
      }
   }, 1000 / Fps);
});