Filling a canvas form with text

I am trying to figure out how to add text to the canvas form for example, here is my code :

var text ="5"; // text to display over the circle
context.fillStyle = "red";
context.beginPath();
context.arc(50,70, 10, 0, Math.PI * 2);
context.closePath();
context.fill(); 

I would really appriciate it if someone helped me add text to the form thanks in advance.

EDIT I understand that I need to write on the canvas again, so this is what I got so far ... but the text does not snap to the center of the circle:

  context.fillStyle = "red";
  context.beginPath();
  var radius = 10; // for example
  context.arc(200, 200, radius, 0, Math.PI * 2);
  context.closePath();
  context.fill();
  context.fillStyle = "black"; // font color to write the text with
  var font = "bold " + radius +"px serif";
  context.font = font;
  context.textBaseline = "top";
  context.fillText(text, 200-radius/4 ,200-radius/2);