// request the user enter a radius size
var rad = prompt("Please enter radius size...","");

// calculate the circle area using (pi*r squared)
var area = Math.PI * (rad * rad);

// calculate the circumference using (2*pi*r)
var circ = 2 * (Math.PI * rad);

// display the results
alert("Area: " + area + "\nCircumference: " + circ);