I am trying to create an isometric game using HTML5 canvas, but don't know how to convert HTML5 canvas screen coordinates to isometric coordinates.
My code now is:

 var mouseX = 0;
 var mouseY = 0;
 function mouseCheck(event) {
 mouseX = event.pageX;
 mouseY = event.pageY;
 }

which gives me canvas coordinates. But how do I convert these coordinates to isometric coordinates? I am using 16x16 tiles.