Unoptimized js code that draws mandelbrot set

<!DOCTYPE html>
<html>

<head>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
  <title>Useful Complex Operations</title>
  <style>
    body {
      text-align: center;
    }
  </style>
</head>

<body onload="mandelbrot()">
    <canvas id=canvas width=1000 height=700>
        Maybe it's time to <a href="http://en.wikipedia.org/wiki/Canvas_element#Support">change</a> browser?
    </canvas>
  <script>
    function Complex(x, y) {
      this.x = x || 0;
      this.y = y || 0;
    } // Complex

    Complex.prototype.toString = function() {
      return this.y >= 0 ? this.x + " + " + this.y + "i" : this.x + " - " + (-this.y) + "i";
    } // toString

    Complex.prototype.modulus = function() {
      return Math.sqrt(this.x*this.x + this.y*this.y);
    } // modulus

    Complex.prototype.add = function(z) {
      return new Complex(this.x + z.x, this.y + z.y);
    } // sum

    Complex.prototype.square = function() {
      return new Complex(this.x*this.x - this.y*this.y, 2*this.x*this.y);
    } // square

    Complex.prototype.sqmod = function(){
        return this.x*this.x + this.y*this.y;
    } // square pow of modulus

    function limitCheck(c, maxIter){
        var z = new Complex(0, 0);
        var i = 1;
        for(; i <= maxIter; i++){
            z = c.add(z.square());
            if (z.modulus() > 2)
                return false; //i here is how fast z grow to fast... it's need to colorize
        }

        return true;
    }

    var scale = 0.005;
    var step = 0.0007;

    var Plot = function(canvas){
        this.ctx = canvas.getContext('2d');
        this.ctx.translate(canvas.width/2, canvas.height/2);
        this.ctx.scale(1/scale, -1/scale);
        this.ctx.fillStyle = "red";
    }

    Plot.prototype.drawRect = function(x, y, w, h, c){
        this.ctx.fillStyle = "rgb(" + c + "," + c + "," + c + ")";
        this.ctx.fillRect(x, y, w, h);
    }

    function mandelbrot(){
        var MAX_X = 2, MAX_Y = 2;
        var plot = new Plot(document.getElementById("canvas"));
        for(var i = -MAX_X; i < MAX_X; i += step){
            for(var j = -MAX_Y; j < MAX_Y; j += step){
                var c = new Complex(i, j);
                var lc = limitCheck(c, 32);
                if(lc == true)
                    plot.drawRect(i, j, step, step, 0);
            }
        }
    }
  </script>
</body>

</html>