Drawing images with JS

Hello I am having issues with making js draw images on a html canvas. This is one thing I have tried (along with others) but it doesn’t work. Please can anyone help me with this.

  window.onload = function() {
    for (i = 0; i < dish1count; i++) {
      xpos = Math.random(300);
      ypos = Math.random(300);
      document.querySelector("left_canvas").getContext("2d").drawImage("images/pillbug.png", xpos, ypos);
    }
  };

Full code completed to this point can be found here.