gistfile1.js

var GameWindow = (function () {
	var my = {},
		//privateVariable = 1,
    canvas,
    context,
    width,
    height,
    scale = 16;   // pixels per unit size. Tank height/width is 1.0 unit size.
  
	//function privateMethod() {
		//// ...
	//}

	//my.moduleProperty = 1;
	//my.moduleMethod = function () {
		//// ...
	//};

  function init() {
    canvas = document.getElementById('gameCanvas');
    context = canvas.getContext('2d');
    width = canvas.width;
    height = canvas.height;
    context.translate(width / 2.0, height / 2.0);
  }

  function drawField() {
    context.beginPath();
    context.rect(0, 0, width, height);
    context.fillStyle = '#99FA99';
    context.fill();
  }

  function scaleCoords(coords){
    { x: (coords.x * scale),
      y: (coords.y * scale);
    }
  }

  my.draw = function(tank){
    drawField();
    tankCoords = scaleCoords(tank);
    context.beginPath();
    context.rect(tankCoords.x - scale/2, tankCoords.y - scale/2, scale, scale);
    context.fillStyle = 'black';
    context.fill();
  }

	return my;
}());