function drawCanvas() {

    // Get our Canvas element

    var surface = document.getElementById("myCanvas");

​

    if (surface.getContext) {

        // If Canvas is supported

        var ctx = surface.getContext('2d');

​

        // Set the clipping area

       // draw rectangle

    ctx.fillStyle = "#09f";

    ctx.fillRect(15,15,70,70);

​

    // set composite property

    ctx.globalCompositeOperation = "source-in";

    // draw circle

   ctx.fillStyle = "black";

    ctx.fillText("WWWWWWWWW",15,15+16);

      ctx.globalCompositeOperation = "source-over";

      ctx.fillStyle = "red";

    ctx.fillRect(60,60,70,70);

    }

}

drawCanvas();