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")        }    }