判断质数-javascript函数

function zhiShu() {
var num = Number(prompt("请输入一个数字"));
var result = true;
for (var i = 2; i <= Math.sqrt(num); i++) {
if (num % i == 0) {
result = false;
break;
}
}
if (result) {
console.log(num + "是质数");
} else {
console.log(num + "不是质数")
}
}