A simple program - but why isn't it working?

Game

var userChoice = prompt("Do you choose rock, paper or scissors?");
var computerChoice = Math.random();
console.log(computerChoice);
if (computerChoice <= 0.33); {
	computerChoice = "rock";	
} else if (computerChoice <= 0.66); {
	computerChoice = "paper";
} else {
	computerChoice = "scissors";
}