JavaScript 判断该数字是否为质数

var num = prompt('请输入一个数字');
function zs(num) {
    var arr = [];
    for (var i = 0; i <= parseInt(Math.sqrt(num)); i++) {
        arr[arr.length] = i;
    }
    var arr1 = [];
    for (let i = 2; i <= arr.length - 1; i++) {
        if (num % arr[i] == 0) {
            arr1.push(0);
        }
    }
    if (arr1[0] == 0) {
        return '这不是质数'
    } else {
        return '这是质数'
    }
}
alert(zs(num));